docs(meta): body-map-viewer measurement results + brief appendix (T-1177/T-1178/T-1154/T-1179/T-1180)
Four results docs under docs/workshops/body-map-viewer/measurements/ and the brief's measurement appendix rewritten from owners/effort to MEASURED headlines: settled hydrology viable (~24 ms/body, 273 bodies ~0.8 s); parallel derive throughput holds 330K-8.3M cells (~64 ms / ~1.8 s); block+tile cost-cleared (deepest step 83K cells ~17 ms); PNG-per-field smallest and fastest with the tagged-envelope migration foreclosed by byte math (21x the ceiling at the smallest size); texture upload a non-issue (8.3M px ~3.2 ms, L8 4-9x cheaper). All numbers post-date the background-load closure with stability re-runs. The workshop round-1 gate is satisfied. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
This commit is contained in:
Claude Fable 5
@@ -216,15 +216,19 @@ necessary (workshops are not closed early on partial convergence).
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tickets drafted by the lead, reviewed by SI; Qatux produces
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`workshop-outcomes.md` and diagram updates.
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## Pre-workshop measurement appendix (owners; numbers land here before round 1)
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## Pre-workshop measurement appendix — MEASURED (2026-07-25, 16-core / Rayon 14 / RX 9070, release builds; all numbers post-date a background-load closure with stability re-runs — details + repro commands in each linked doc)
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| # | Measurement | Owner | Effort |
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**The gate is satisfied: ①–④ measured, ⑤ measured. Round 1 may start.**
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| # | Ticket | Headline result | Doc |
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|---|---|---|---|
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| ① | Equilibrium hydrology solver prototype + bench (512×256 and 4K-class) incl. cliff representation output | Dudley | 1–2 d |
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| ② | Per-gridunit derive at real canvas sizes (330K and 8.3M cells, production par_iter path — no extrapolation) | Dudley | 0.5 d |
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| ③ | T-1154 block/tile rung costs (now unblocked) — prices the ladder's bottom | Dudley | 0.5 d |
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| ④ | Wire-size table for candidate encodings (raw/bit-packed/RLE/PNG; MessagePack round-trip on one real canvas) | Araminta + Dudley | 0.5 d |
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| ⑤ | Godot ImageTexture upload cost per step-cross (330K–8.3M px) | Stig | 0.25 d |
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| ① | T-1177 | **Settled hydrology VIABLE**: 512×256 ~24 ms/body; all 273 bodies Rayon-parallel ~0.7–0.8 s; 8.3M cells ~5.7 s single-thread (no production path needs it synchronously). Cliff representation: dominant height + `channel_depth` + `cliff_edge` flag. Finding: gorge carving is structurally RARE (priority-flood finds true spill levels; zero carved cells at production scales — needs chained-basin geometry). Solver: priority-flood + Dijkstra overflow, pure function, determinism-proved. | [t1177](measurements/t1177-hydrology.md) |
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| ② | T-1178 | **Parallel throughput HOLDS at scale** (the T-1143 extrapolation gap, closed): ~190–220 ns/cell parallel flat from 330K→8.3M cells; 330K canvas ~64 ms, 2.07M ~0.4 s, 8.3M ~1.7–1.8 s (7.5–8.8× speedup); single-thread flat ~1.65 µs/cell, matches prior baseline within 8%. Cross-validated on three bodies incl. real courses. Measured through the real `build_district_window_layer`. | [t1178+t1154](measurements/t1178-t1154-derive-bench.md) |
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| ③ | T-1154 | **Block GO, Tile GO on cost** (~1.8–1.9 µs/cell, same band as District/Quarter). Octave cutoff buys ZERO below District spacing (verified: wavelength table bottoms at 128 m). Deepest-step realistic canvas (216×384 m @ 1 m = 83K cells): **~17 ms parallel — trivially interactive**. `voxel_relief` already in the Atlas path; `voxel_mosaic` untouched by it. Real gates are wire carrier + D-226(d) canvas policy, not cost. | [t1178+t1154](measurements/t1178-t1154-derive-bench.md) |
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| ④ | T-1179 | **PNG-per-field wins everywhere** — smallest AND fastest: 330K canvas = 638 KB (0.32× raw, 5.4/3.6 ms enc/dec) vs raw rmp 1.99 MB; RLE loses to raw (elev/temp near-noise per cell). **Tagged-envelope migration foreclosed as necessary**: best case is 21× the 30 KB ceiling at the SMALLEST size (563× at 8.3M). Corrected density: 6.00 B/cell measured raw. | [t1179](measurements/t1179-wire-table.md) |
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| ⑤ | T-1180 | **Upload cost is a non-issue**: worst case (8.3M px RGBA8 create) ~3.2 ms median, ~2.4–2.9 ms frame-delta spike — never near the 16.6 ms budget. **L8 is 4–9× cheaper at every size** (~0.5–0.7 ms at 4K). Prefer `texture.update` reuse on step-cross; use L8 for single-channel planes. Windowed-only measurement (headless renderer fakes uploads). | [t1180](measurements/t1180-imagetexture.md) |
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Bench code (all `#[ignore]`d release tests): `server/src/atlas/hydrology_equilibrium.rs` + `server/tests/hydrology_equilibrium_bench.rs`, `server/tests/bmv_gridunit_bench.rs`, `server/tests/wire_encoding_bench.rs`.
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## Input Documents
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@@ -0,0 +1,393 @@
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---
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title: "T-1177 — equilibrium hydrology solver prototype + bench (512×256 and 4K-class) incl. cliff representation (measurement ①)"
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workshop: body-map-viewer
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status: complete
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owner: Dudley
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---
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# T-1177 — equilibrium hydrology solver prototype + bench
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Measurement ① of the [body-map-viewer workshop
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brief](../body-map-viewer-workshop-brief.md)'s pre-workshop appendix, per
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[tyre-implications.md §3](../tyre-implications.md) item 1 — the highest-priority,
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biggest-unknown measurement, named as the one that could invalidate per-body-open
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settled hydrology outright if costs land in seconds, not milliseconds. Also the
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mandatory output for **red flag 4** (the cliff/multi-height data-model gap).
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## Environment note (read first)
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A background Factorio process was running on this machine for part of this
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session and may have starved CPU before the coordinator's mid-session notice.
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**No benchmark timing in this document predates the coordinator's closure
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notice.** Concretely: module compilation, unit-test authoring, and the
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fixture-design investigation (see "Gorge carving — the honest story" below)
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all happened before and after the notice, but every `ms`/`ns` figure reported
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below was captured **after** the notice, with `/proc/loadavg` checked
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immediately before each timed run (observed 1-minute load between 0.5 and 5.6
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throughout the timed portion of this session — never during the
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Factorio-shutdown settling spike). The three headline cases (512×256,
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768×432, 3840×2160) were each run twice — once during the initial measurement
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pass, once as a final stability re-run — and landed within ~1-3% of each
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other both times (see the "Stability re-run" row in the results table), so
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there is no early-slow/later-fast delta to misattribute to warm-up or
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optimization.
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## What was built
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New module: `server/src/atlas/hydrology_equilibrium.rs` (registered in
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`server/src/atlas/mod.rs`). New bench file:
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`server/tests/hydrology_equilibrium_bench.rs`. No other files touched.
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`solve(elevation, width, height, sea_level, climate) -> HydrologyResult` is a
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pure function of its four arguments (deterministic per D-010) — no RNG, no
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wall-clock, no `HashMap` iteration anywhere in the call graph. It is **not** a
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stateful simulation: there is no tick loop, no iterative erosion-over-time
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model, no rainfall accumulation across steps. One elevation field in, one
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settled hydrology result out, same every time.
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### Algorithm (priority-flood family, Barnes/Planchon-Darboux class)
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1. **Priority-flood fill** (`priority_flood_fill`): a min-heap seeded at
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every below-sea-level cell AND every top/bottom grid-edge cell (mirroring
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`drainage.rs`'s own row-bounded D8 walk — the equirectangular grid has no
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pole neighbor, so those rows are boundary the same way a coastline is).
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Standard "flood from the outside in": repeatedly pop the lowest-water-level
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frontier cell, raise each unvisited neighbor to
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`max(neighbor_original, popped_level)`. `O(n log n)`, one pass, versus
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`drainage.rs`'s existing `depression_fill` which is an iterative relaxation
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(up to 10 full-grid passes) of a *similar* problem but does not expose
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basin membership or spill points — this module needed both, so it
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re-derives the fill with a heap that tracks them, rather than layering
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basin-detection on top of that existing black-box result.
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2. **Lake cells + basin grouping**: any cell where `filled > original` is a
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lake cell; contiguous (8-connected) lake cells are grouped into basins via
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BFS flood-fill (`label_lake_basins`), ids assigned in row-major discovery
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order for determinism.
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3. **Spill point + spill level per basin**: the basin-boundary cell whose
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OUTSIDE neighbor has the lowest *original* (unfilled) elevation — i.e. the
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genuine topographic saddle, not merely "any lake cell touching non-basin
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terrain" (an early draft ranked by the boundary cell's own *filled*
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elevation, which degenerates to an arbitrary tie-break on a uniformly-filled
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lake, since every boundary cell of a flat lake shares the same filled
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value — see "Gorge carving" below for how this surfaced). The spill level
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is that spill cell's own `filled` value — the lake's water surface at
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overtopping.
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4. **Endorheic classification** (`is_endorheic`, moisture-governed, see
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below): large + dry basins are declared closed water-cycle sinks
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(`BasinOutcome::Endorheic`, mapped to `RIVER_DOWNSTREAM_TERMINAL` for
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consumers — see "Reuse of the TERMINAL sentinel").
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5. **Overflow path** (`cheapest_overflow_path`, Dijkstra/A*-family, same
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`BinaryHeap<Reverse<(cost, idx)>>` pattern `road_graph.rs`'s own `astar`
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uses): from the spill point, cost = cumulative elevation carved above the
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basin's own spill level (0 for any step at or below it). Terminates at the
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first cell that is below sea level (`Sea`), belongs to a *different*
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already-resolved basin (`Basin(id)` — the chaining case), or is open low
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ground not otherwise claimed (`EdgeUnreachable`, the lake-fill analogue of
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`drainage::RIVER_DOWNSTREAM_EDGE_DRAIN`). Basins are processed in ascending
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spill-level order so a lower basin is always resolved before a higher one
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could chain into it.
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6. **Carving**: every path cell whose elevation exceeds the basin's spill
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level is cut down to it — `channel_depth_scaled[cell] = original[cell] -
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spill_level`, `cliff_edge[cell] = true` — but ONLY when the path's peak
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flow accumulation (reusing a D8 flow-direction/accumulation pass over the
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*filled* surface, same algorithm as `drainage.rs`) clears
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`RIVER_THRESHOLD = 200` (mirroring `drainage::RIVER_THRESHOLD`): a
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trickling overflow through near-flat ground doesn't get a canyon.
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### Reuse of the TERMINAL sentinel
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The ticket flagged `RIVER_DOWNSTREAM_TERMINAL` (`body_world_state.rs`,
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value 10) as "reserved, unused in round 1 — future endorheic basin." Confirmed
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by reading `river_course.rs::build_edges` (T-1170): it already special-cases
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`sentinel == RIVER_DOWNSTREAM_TERMINAL` as a no-op skip, so a consumer that
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starts emitting it does not break any existing code path — this prototype's
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`BasinOutcome::Endorheic` is exactly the case that sentinel was reserved for,
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and mapping to it at the wire-integration stage (not built in this
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prototype — see "What this prototype does NOT do") is additive, not a
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migration.
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## Measured numbers
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**Hardware:** 16 logical cores (Intel Core i9-9900K @ 3.60GHz), Rayon default
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pool (`std::thread::available_parallelism() == 16`, confirmed in the parallel
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bench's own printed output). Release build (`cargo build --release`), bench
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invocation:
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```bash
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cd server
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cargo test --release --test hydrology_equilibrium_bench <test_name> -- --ignored --nocapture
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```
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Cold = first `solve()` call in the process; warm = second call, same input,
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same process (allocator/cache warm). All entries below are **MEASURED**, none
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extrapolated.
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| Grid | Cells | Cold total | Cold ns/cell | Warm total | Warm ns/cell | Basins | Lake cells | Carved cells |
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|---|---|---|---|---|---|---|---|---|
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| 512×256 (real GJ1c) | 131,072 | 24.36–24.97 ms | 185.8–190.5 | 23.61–24.58 ms | 180.1–187.5 | 68 (66 overflow, 2 endorheic) | 4,623 | 0 |
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| 768×432 (synthetic, ~330K) | 331,776 | 72.32–72.97 ms | 218.0–219.9 | 69.03–69.98 ms | 208.1–210.9 | 103 (all overflow) | 16,617 | 0 |
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| 3840×2160 (synthetic, ~8.3M) | 8,294,400 | 5,671.84–5,711.82 ms | 683.8–688.6 | 5,699.31–6,065.91 ms | 687.1–731.3 | 102 (all overflow) | 412,700 | 0 |
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Each grid's range is the initial measurement pass and the final stability
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re-run (both post-Factorio-closure, low load throughout) — the two numbers
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per cell agree within ~1-3%, confirming stability, not a warm-up or
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optimization effect.
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**Parallel throughput (273 independent bodies, 512×256 each, Rayon
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`par_iter`)** — the real production shape (hydrology is solved once per body,
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not internally parallelized within one solve; see "Why solve() isn't
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internally parallelized" below):
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| Run | Total | ms/body |
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|---|---|---|
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| Initial | 826.30 ms | 3.03 |
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| Stability re-run | 718.18 ms | 2.63 |
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**273 bodies' worth of 512×256 hydrology solves complete in well under one
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second (0.7–0.8 s) on this 16-core machine.**
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### Why `solve()` isn't internally parallelized
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Both the priority-flood fill and the Dijkstra overflow search are globally
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sequential by construction — a shared min-heap with a strict pop order, same
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as `road_graph.rs`'s own `astar` (also unparallelized, same `BinaryHeap`
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pattern). This is architecturally identical to why `layer_proxy.rs`'s
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row-chunked `par_iter` win doesn't apply here: that speedup comes from each
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*cell* being an independent pure function (D-227); hydrology's basins and
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paths are NOT independent of each other within one body (a basin's outcome
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can depend on a lower basin having already been resolved — the chaining
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case). What DOES parallelize cleanly, and is exactly the production shape, is
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solving **different bodies'** hydrology concurrently — measured above.
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### Determinism proof
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`server/tests/hydrology_equilibrium_bench.rs::determinism_at_330k_cells`
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solves the 768×432 synthetic grid twice and asserts the full result
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(`filled_scaled`, `channel_depth_scaled`, `cliff_edge`, and every basin's
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`cells`/`spill_level_scaled`/`spill_cell`/`outcome`) is byte-identical across
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both solves. Passes (`cargo test --release --test hydrology_equilibrium_bench
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determinism_at_330k_cells -- --ignored --nocapture`). The module's own unit
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tests (`server/src/atlas/hydrology_equilibrium.rs`, 15 tests, `cargo test
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--lib atlas::hydrology_equilibrium`) additionally cover determinism at
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smaller synthetic grids (64×32, 96×48) including basins that classify
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Overflow and basins that classify Endorheic.
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## The endorheic criterion (explicitly tunable)
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```rust
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const ENDORHEIC_AREA_FLOOR: f64 = 0.004; // ~0.4% of body surface
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const ENDORHEIC_MOISTURE_CEILING: i32 = 60; // 0-100 scale
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fn is_endorheic(area_frac: f64, moisture_q: i32) -> bool {
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area_frac >= ENDORHEIC_AREA_FLOOR && moisture_q <= ENDORHEIC_MOISTURE_CEILING
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}
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```
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A basin is declared endorheic (closed water cycle, no outflow) when it is
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BOTH large enough that its own evaporative surface plausibly balances its
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catchment's inflow (bigger basin = more evaporating surface per unit of
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catchment — Great-Salt-Lake/Caspian-style) AND the body isn't wet enough that
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evaporation is unlikely to keep pace (`moisture_q`, mirroring
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`district_profile::derive_moisture_q`'s hydrosphere-derived ceiling before
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the per-district spatial gradient — one body-wide value, not a per-basin
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value; see "does NOT do" below). This is a **first-pass heuristic, not a
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calibrated physical model** — the two constants and the boolean-AND shape are
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placeholders. On the GJ1c body at moisture_q=55, 2 of 68 basins classified
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endorheic; on the two synthetic multi-octave grids at moisture_q=55, zero did
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(the synthetic terrain's basins are all smaller/shallower than
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`ENDORHEIC_AREA_FLOOR` at those grid resolutions). Unit tests
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(`is_endorheic_large_dry_basin_is_endorheic`,
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`is_endorheic_tiny_basin_always_overflows`,
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`is_endorheic_wet_body_always_overflows`,
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`large_dry_basin_classifies_endorheic`) lock the criterion's *shape* (both
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gates matter, area alone or moisture alone isn't enough) without pretending
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the specific constants are calibrated — that calibration is future work
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(parallel to Q-123, which already tracks provisional-pending-calibration
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magnitudes for the district moisture gradient this module's `ClimateInputs`
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borrows from).
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## Gorge carving — the honest story (cliff representation input, red flag 4)
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**All three production-scale benches (512×256, 768×432, 3840×2160) report
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zero carved gorge cells.** This is a genuine, investigated measurement
|
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result, not a code defect — verifying it required a substantial fixture
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investigation (documented in the module's own test comments,
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`server/src/atlas/hydrology_equilibrium.rs`, the "Gorge carving" test
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section) that surfaced a structural property of priority-flood itself, worth
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stating plainly for the workshop:
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**Priority-flood finds the TRUE global minimum enclosing rim of a basin,
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swallowing any monotonically-non-decreasing connected run of cells into the
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same lake and adopting that run's own peak as the basin's real spill level.**
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Since the overflow search's carving threshold is that SAME spill level, the
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first cell the search reaches outside the lake is — by construction of how
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the spill level was computed — never higher than spill level. A single
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sealed basin's own rim, however jagged, therefore **always carves zero**
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under this algorithm: the water simply rises to meet whatever the true
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lowest crossing is. Several `solve()`-level fixtures (a basin behind a single
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ridge with a saddle; a basin behind a saddle-then-hump; a basin chained into
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a second, higher-floor basin via a monotonic ramp) were built and each
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converged on zero carved cells for exactly this reason, once traced through.
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Genuine carving is only possible in a **narrower geometry**: two
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independently-sealed basins (each with its own valid, separately-computed
|
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rim) connected by a corridor that is (a) a single cell wide in *both* grid
|
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dimensions — not a multi-cell monotonic run the flood can absorb into either
|
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basin's own lake — and (b) higher than *both* basins' independent rims (else
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the two basins simply flood-merge into one, and merging means the "gorge"
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was never real, just the wrong basin count). This is real terrain (a narrow
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saddle connecting two separately-perched valleys, each already full) but
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comparatively rare at continental (512×256–3840×2160) working-grid
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resolution — consistent with all three production-scale benches finding
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zero.
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Given the difficulty of constructing an end-to-end `solve()` fixture for
|
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that narrow geometry without also accidentally merging or absorbing the
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basins (four fixture iterations attempted, each correctly diagnosed as
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"basins merged" or "spill level absorbed the connector" rather than "bug"),
|
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the carving *mechanism itself* — `cheapest_overflow_path`'s Dijkstra search
|
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and the `original[cell] - spill_level` carving arithmetic — is verified
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directly with hand-constructed inputs instead
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(`cheapest_overflow_path_finds_the_true_minimum_crossing`,
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`cheapest_overflow_path_prefers_lower_total_cost_over_shorter_path`,
|
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`carving_arithmetic_matches_original_minus_spill_level`, all passing). These
|
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confirm: the search correctly routes through a genuinely-lower gap instead of
|
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an impassable wall; cost accumulates correctly across multiple
|
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above-spill-level cells in sequence (not just a single-cell threshold); and
|
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the exact formula `solve()` uses to populate `channel_depth_scaled`/
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`cliff_edge` is arithmetically correct in isolation.
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||||
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||||
**Practical read for the workshop:** at the working-grid resolutions this
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system actually runs at, gorge carving will be a **rare, not a routine**
|
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event — most basins settle by simple lake-fill, not canyon-cutting. The data
|
||||
model still needs to represent it when it happens (below), but the
|
||||
cliff/multi-height case is the exception, not the common path, which may
|
||||
ease the "how often does the payload need the vertical-structure field"
|
||||
half of red flag 4's cost question (a wire-frequency question for
|
||||
measurement ④, not answered here).
|
||||
|
||||
### The cliff representation proposal
|
||||
|
||||
Grounded in what the solver actually computes (`channel_depth_scaled` +
|
||||
`cliff_edge`, both already per-cell fields on `HydrologyResult`):
|
||||
|
||||
**Dominant height + channel-depth field + cliff-edge flag** (the first option
|
||||
red flag 4 named, and the one this solver's own output shape falls out of
|
||||
directly, not chosen independently of the measurement):
|
||||
|
||||
- `elevation` (existing field) carries the **rim/dominant height** — the
|
||||
gridunit's visible/walkable surface for anything that isn't inside the
|
||||
carved channel. No change to the existing single-height payload contract
|
||||
for the common (non-gorge) case.
|
||||
- `channel_depth: u16` (or similar, quantized) — 0 everywhere except carved
|
||||
gorge cells, where it is the vertical drop from `elevation` down to the
|
||||
channel floor. This is a **direct, non-lossy carry** of
|
||||
`channel_depth_scaled` — no re-derivation needed downstream, the solver
|
||||
already computes exactly this number.
|
||||
- `cliff_edge: bool` (or foldable into a 1-bit flag alongside existing
|
||||
classification bytes) — marks the gridunit as a rim/discontinuity cell, so
|
||||
the client map-art function knows to render a cliff-face style transition
|
||||
rather than a smooth gradient at that gridunit's boundary. Also a direct
|
||||
carry of the solver's own `cliff_edge` field.
|
||||
|
||||
**Why not min/max height pair:** a min/max pair loses the *shape* of the
|
||||
transition (is the low value a point drop at one edge, or does it span the
|
||||
whole gridunit?) that `channel_depth` + `cliff_edge` preserves implicitly (a
|
||||
cliff-edge-flagged gridunit's channel floor is `elevation - channel_depth`,
|
||||
and the flag itself tells the renderer this gridunit is an edge, not an
|
||||
interior channel cell — interior channel cells one gridunit further in would
|
||||
carry the depth without the edge flag, letting the map-art function
|
||||
distinguish "this is the canyon wall" from "this is the canyon floor,
|
||||
already below the general terrain"). Min/max is also a less direct fit to
|
||||
what the solver computes — it would require deriving two synthetic heights
|
||||
per gridunit from the single `channel_depth_scaled` number the solver
|
||||
actually produces, an extra derivation step for no informational gain over
|
||||
carrying the depth directly.
|
||||
|
||||
**Scope note (does not resolve red flag 4 alone):** this proposal answers
|
||||
"what data does a carved gorge gridunit carry" — it does NOT resolve whether
|
||||
this lives on the Atlas per-gridunit payload at Phase-4 scope (a wire/schema
|
||||
decision for Araminta's ③/④ work and the workshop's synthesis round) or is
|
||||
deferred to Phase-5 in-world geometry with only a "steep" classification
|
||||
surfacing on the map. Given carving is measured as **rare** at working-grid
|
||||
resolution (above), the wire-cost argument for including a rarely-populated
|
||||
optional field is weaker than red flag 4's framing assumed — worth
|
||||
surfacing as new information for that decision, not just cost data for a
|
||||
decision already assumed necessary.
|
||||
|
||||
## What this prototype does NOT do
|
||||
|
||||
- **No stateful simulation.** No tick loop, no time-stepped erosion, no
|
||||
rainfall-accumulation-over-time model. `solve()` is called once per body
|
||||
(or per working-grid downsample) and produces a settled end-state — this
|
||||
is deliberate (the workshop premise: "deterministic equilibrium... a
|
||||
settled end-state, pure function of seed + moisture/climate"), not a
|
||||
scope gap, but stated explicitly since it bears directly on the
|
||||
"geological backstory computed at generation time" framing.
|
||||
- **No per-basin moisture/climate lookup.** `ClimateInputs::moisture_q` is a
|
||||
single body-wide value (mirroring `derive_moisture_q`'s hydrosphere-derived
|
||||
ceiling, before the per-district latitude/elevation/continentality
|
||||
gradient). A real implementation would likely want the endorheic
|
||||
criterion to read each basin's own local climate (a basin near the pole
|
||||
vs. the equator on the same body plausibly differs), which requires
|
||||
wiring in per-district or per-region climate context
|
||||
(`BodyWorldState.districts`/`regions`) — not built here.
|
||||
- **No wire/schema integration.** `HydrologyResult`/`Basin`/`BasinOutcome`
|
||||
are prototype-only types, not wired into `RiverNetwork`,
|
||||
`DrainageBasin`, or any `AtlasLayerResponse` payload. The `TERMINAL`
|
||||
sentinel reuse (above) is confirmed safe/additive but not implemented as
|
||||
a wire integration — that's downstream work once the workshop rules on
|
||||
the wire contract (measurement ④, Araminta's track).
|
||||
- **No production-scale gorge carving observed.** As detailed above, all
|
||||
three production-scale benches carved zero cells — the carving code path
|
||||
is verified correct via direct unit tests of the mechanism, not via an
|
||||
end-to-end production-scale example. Real terrain (actual planetary
|
||||
heightmaps beyond GJ1c) may or may not produce the narrow geometry that
|
||||
triggers carving more often; this prototype did not survey other bodies.
|
||||
- **No re-run against `drainage.rs`'s existing `depression_fill`/basin
|
||||
labeling for cross-validation.** This module's priority-flood is a
|
||||
structurally different (heap-based, single-pass) implementation of a
|
||||
similar problem to `drainage.rs`'s iterative relaxation; the two were not
|
||||
compared cell-for-cell against each other on the same input. They are not
|
||||
required to agree (different purposes — `drainage.rs`'s fill feeds D8 flow
|
||||
direction for river extraction; this module's fill feeds basin/spill
|
||||
detection), but a reader should not assume they'd produce identical
|
||||
filled surfaces.
|
||||
- **No chunk-boundary/step-boundary decomposition.** The solver runs on a
|
||||
single contiguous elevation grid start-to-finish (matching how
|
||||
`drainage::analyze` is called today — once per body, on the Layer-1
|
||||
512×256 working grid). Whether/how hydrology decomposes across the
|
||||
step-ladder's per-step canvases (premise 8: "step boundaries = compute-
|
||||
chunk boundaries") is a synthesis-round question, not addressed here —
|
||||
the measured costs above are for a full single-grid solve at each listed
|
||||
size, not a chunked partial re-solve.
|
||||
- **`RIVER_THRESHOLD` reused, not re-derived per body.** The gorge-carving
|
||||
flow-accumulation gate uses the same fixed `RIVER_THRESHOLD = 200`
|
||||
`drainage.rs` uses globally — not the per-district `river_threshold`
|
||||
DistrictProfile carries downstream (D-239 §1). Fine for a prototype
|
||||
measuring solver cost; a production integration should probably use the
|
||||
same per-district value other consumers do.
|
||||
|
||||
## Verdict
|
||||
|
||||
**Per-body-open settled hydrology is viable.** Headline numbers: 512×256
|
||||
solves in ~24 ms single-threaded; the full 4K-class 8.3M-cell grid solves in
|
||||
~5.7 s single-threaded (a genuine, not extrapolated, "computer catches fire"
|
||||
ceiling case — but note no production path actually derives hydrology at
|
||||
8.3M cells synchronously; see below); and the realistic production shape —
|
||||
273 independent bodies at the real 512×256 working-grid size, run in
|
||||
parallel across the Rayon pool — completes in well under a second (0.7–0.8
|
||||
s). This closes the exact gap the T-1143 planetary rung died of: the
|
||||
biggest-unknown, highest-priority measurement is now a real number, not an
|
||||
extrapolation, and it does not invalidate the "settled hydrology" premise.
|
||||
|
||||
**Caveat worth carrying into the workshop:** the 8.3M-cell single-solve
|
||||
number (~5.7 s) is a genuine cost that would matter if any single request
|
||||
path needed hydrology re-solved synchronously at that size on demand. Given
|
||||
this module's `solve()` isn't currently wired into any request path (see
|
||||
"does NOT do" above), whether that number is ever actually paid at request
|
||||
time — or only ever paid once per body, offline/precomputed, the same way
|
||||
`drainage::analyze` already runs once per body today — is a caching/
|
||||
architecture question for the workshop's cache-tier synthesis (Dudley's
|
||||
question 4 / red flag 2), not a solver-cost question this measurement can
|
||||
settle alone.
|
||||
@@ -0,0 +1,441 @@
|
||||
---
|
||||
title: "T-1178/T-1154 — per-gridunit derive bench at real canvas sizes + block/tile rung costs (measurements ②/③)"
|
||||
workshop: body-map-viewer
|
||||
status: complete
|
||||
owner: Dudley
|
||||
---
|
||||
|
||||
# T-1178/T-1154 — derive bench at real canvas sizes + the ladder's bottom rungs
|
||||
|
||||
Measurements ②/③ of the [body-map-viewer workshop
|
||||
brief](../body-map-viewer-workshop-brief.md)'s pre-workshop appendix, per
|
||||
[tyre-implications.md §3.2](../tyre-implications.md) item 2 and item 4. This is
|
||||
the anti-extrapolation gap the T-1143 planetary-rung post-mortem named by name:
|
||||
does the row-chunked `par_iter` throughput measured at the shipped 4,096-cell
|
||||
window ceiling (`docs/architecture/atlas-zoom-ladder-t1143.md` §7: 1.785
|
||||
µs/cell District cutoff, 1.454 µs/cell orbital, 0.617 ms/served-window) HOLD
|
||||
at real step-canvas sizes (330K–8.3M cells), and what does the ladder's
|
||||
un-costed bottom (block/tile) actually cost. Every number below is labelled
|
||||
**MEASURED** or **ARITHMETIC** — nothing is extrapolated from a smaller
|
||||
measured size to a larger unmeasured one.
|
||||
|
||||
## Environment note (read first)
|
||||
|
||||
A background Factorio process was running on this machine for part of this
|
||||
session and may have starved CPU before and during initial harness
|
||||
compilation. **It was closed partway through this session, before any timing
|
||||
measurement in this document was captured or kept.** Concretely:
|
||||
|
||||
- Every `ms`/`ns` figure in this document either post-dates the closure, or is
|
||||
an explicit **stability re-run performed after it** (see "Stability
|
||||
re-runs" below) — no pre-closure number is reported anywhere in this doc.
|
||||
- Load average was watched (`uptime`) before every timed run; each run below
|
||||
was started only once the 1-minute load average had settled to single
|
||||
digits on this 16-core machine (typically 1.3–5.0), never during the
|
||||
post-closure settling spike (which peaked ~25 immediately after closure and
|
||||
fell within ~2 minutes).
|
||||
- Per the coordinator's instruction: any early-slow/later-fast delta observed
|
||||
during this session is **not reported as a chunking or warm-up finding** —
|
||||
it is attributed to environmental noise and excluded. The findings below
|
||||
(parallel throughput holding flat from 330K→8.3M) are confirmed by
|
||||
re-running the headline cases a second time on the quiet machine, not by a
|
||||
single early/late comparison.
|
||||
- The baseline figures this document compares against (1.785 µs/cell
|
||||
District, 1.454 µs/cell orbital, 0.617 ms/served-window,
|
||||
`atlas-zoom-ladder-t1143.md` §7) were measured in an **earlier session**
|
||||
under unknown load conditions. Where this session's quiet-machine numbers
|
||||
come out *faster* than that baseline (they do, substantially — see below),
|
||||
that is flagged explicitly as an environment-conditions caveat, not claimed
|
||||
as a genuine speedup from any code change. No code in the derive path
|
||||
changed between sessions.
|
||||
|
||||
## What was measured
|
||||
|
||||
**Body/fixtures:** two independent fixtures, deliberately not just one:
|
||||
|
||||
1. **Synthetic gradient body** (`bench_hm()`/`bench_ta()`, same fixture
|
||||
`zoom_ladder_bench.rs` uses) — 128×64 working grid, deterministic smooth
|
||||
gradient, no PNG I/O. Body id `"bench"`, seed
|
||||
`SeedChain::root(99).derive(SeedDomain::Body, 1)`. Used for every sweep
|
||||
below except the two crosschecks.
|
||||
2. **Real committed GJ1c heightmap** (`wiki/star-systems/GJ-1/bodies/GJ1c/heightmap.png`,
|
||||
downsampled to the production 512×256 working grid, real river network via
|
||||
`drainage::analyze`), seed `SeedChain::root(0xC0FFEE_u64).derive(SeedDomain::Body, 7)`
|
||||
— used for one 330K-cell cross-check to confirm the synthetic-fixture
|
||||
numbers are not an artifact of a trivial gradient or an empty river
|
||||
network. The window is centred on a real GJ1c river cell (not the world
|
||||
origin — an origin-centred window on GJ1c measured `courses_in_window=0`
|
||||
on a first attempt and was corrected; see the bench source's doc comment).
|
||||
|
||||
**Hardware:** 16 logical cores (Intel Core i9-9900K @ 3.60GHz),
|
||||
`std::thread::available_parallelism() == 16`, no `RAYON_NUM_THREADS` override
|
||||
— Rayon's global default pool uses all 16 (`rayon::current_num_threads()`
|
||||
confirmed `16` in every parallel run's own printed output, reported inline
|
||||
per-run below rather than assumed).
|
||||
|
||||
**Code:** new file `server/tests/bmv_gridunit_bench.rs` (per the batch
|
||||
instruction — `server/src/atlas/mod.rs` untouched, `zoom_ladder_bench.rs`
|
||||
untouched, this workshop-gate pass kept in its own file since it measures a
|
||||
different SHAPE question than that file's fixed-4,096-cell sweeps). All
|
||||
benches `#[ignore]`d release tests, `cargo test --release --test
|
||||
bmv_gridunit_bench -- --ignored --nocapture`.
|
||||
|
||||
**Invocation used for every number below** (run individually per test name,
|
||||
not `-- --ignored` for the whole file at once, so each run's wall time isn't
|
||||
diluted by unrelated tests still warming up):
|
||||
|
||||
```bash
|
||||
cd server
|
||||
cargo test --release --test bmv_gridunit_bench <test_name> -- --ignored --nocapture
|
||||
```
|
||||
|
||||
---
|
||||
|
||||
## T-1178 (Measurement ②) — does par_iter throughput hold at real canvas sizes?
|
||||
|
||||
### The `n`-cap problem — what "production path" means here
|
||||
|
||||
`build_district_window_layer`'s CALLER (`handle_atlas_request` via
|
||||
`clamp_window_n_v2`) hard-clamps `n` so the derived cell grid never exceeds
|
||||
`WIRE_CAP_CELLS = 4,096` — **a real client can never request a 330K-cell
|
||||
window over the wire, by design** (D-226 T-1124 §2, the windowed-family
|
||||
ceiling). So "run it through the production path at 330K/8.3M cells" cannot
|
||||
mean "send an `AtlasLayerRequest` for that size" — no such request is legal.
|
||||
|
||||
Confirmed by direct read this session
|
||||
(`server/src/atlas/layer_proxy.rs:1515-1628`): `build_district_window_layer`
|
||||
itself has **no internal clamp** — the clamp lives one layer up, in the
|
||||
request handler. So this measurement calls the actual, unmodified
|
||||
`build_district_window_layer` function directly — same signature, same
|
||||
row-chunked `into_par_iter()` loop (`layer_proxy.rs:1564-1586`), same
|
||||
`derive_window_cell`/`scatter_row` internals, same `derive_at_metres` calls —
|
||||
at an `n` no wire request could carry. This is exactly what the ticket
|
||||
anticipates ("bench the underlying chunked loop at those counts and say
|
||||
exactly what you ran").
|
||||
|
||||
### Square vs. rectangular canvas
|
||||
|
||||
`build_district_window_layer` only derives SQUARE `side×side` grids (`n` is a
|
||||
single extent — no rectangle parameter exists). The named real step-canvas
|
||||
shapes are 16:9 rectangles. Two measurements were taken per cell-count
|
||||
target:
|
||||
|
||||
1. **Square, through the real `build_district_window_layer` function**
|
||||
(nearest square side to the target cell count: 576²=331,776,
|
||||
1440²=2,073,600, 2880²=8,294,400 — landing exactly on 330K/2.07M/8.3M).
|
||||
2. **Real 16:9 rectangle** (768×432, 1920×1080, 3840×2160), via a
|
||||
hand-written row-chunked replica loop that mirrors
|
||||
`build_district_window_layer`'s internals cell-for-cell (same
|
||||
`into_par_iter()` row chunking, same `derive_at_metres` call per cell,
|
||||
same per-cell output-field quantization `derive_window_cell` performs) —
|
||||
necessary because no production entry point derives a non-square window.
|
||||
Labelled **MEASURED (replica loop)** below to distinguish from **MEASURED
|
||||
(production fn)**.
|
||||
|
||||
Both converge on the same rate at the same cell count (see table) — the
|
||||
replica loop is a faithful stand-in.
|
||||
|
||||
### Headline table — District spacing, cutoff=2,048m (the shipped District band)
|
||||
|
||||
| Canvas | Cells | Path | Parallel (16 threads) | ns/cell parallel | Single-thread | ns/cell single-thread | Speedup |
|
||||
|---|---:|---|---:|---:|---:|---:|---:|
|
||||
| 330K (square, side=576) | 331,776 | MEASURED (production fn) | 63.69 ms | 192.0 | 547.45 ms | 1,650.1 | 8.60× |
|
||||
| 330K (768×432) | 331,776 | MEASURED (replica loop) | 63.58 ms | 191.6 | 544.51 ms | 1,641.2 | 8.56× |
|
||||
| 2.07M (square, side=1440) | 2,073,600 | MEASURED (production fn) | 394.61 ms | 190.3 | 3,436.18 ms | 1,657.1 | 8.71× |
|
||||
| 2.07M (1920×1080) | 2,073,600 | MEASURED (replica loop) | 423.20 ms | 204.1 | 3,383.64 ms | 1,631.8 | 7.99× |
|
||||
| 8.3M (square, side=2880) | 8,294,400 | MEASURED (production fn) | 1,827.34 ms | 220.3 | 13,767.58 ms | 1,659.9 | 7.53× |
|
||||
| 8.3M (3840×2160) | 8,294,400 | MEASURED (replica loop) | 1,731.38 ms | 208.7 | 13,584.42 ms | 1,637.8 | 7.85× |
|
||||
|
||||
**All six rows MEASURED — none extrapolated.** Parallel per-cell rate is flat
|
||||
across every canvas size (190.3–220.3 ns/cell, the full spread is ~15% —
|
||||
consistent with run-to-run scheduling noise on the same machine, not a trend;
|
||||
see "Stability re-runs"). **This directly answers T-1178's central question:
|
||||
the row-chunked `par_iter` throughput measured at 4,096 cells holds at 330K,
|
||||
2.07M, and 8.3M cells — no degradation from memory pressure, cache behavior,
|
||||
or Rayon chunking overhead at any tested size.**
|
||||
|
||||
**Environment caveat (required):** these parallel per-cell rates (~190–220
|
||||
ns/cell) are **substantially faster** than the earlier-session baseline
|
||||
(1.785 µs/cell District cutoff at 4,096 cells, `atlas-zoom-ladder-t1143.md`
|
||||
§7) — roughly 8–9× faster per cell. This gap is **not** claimed as a
|
||||
per-cell speedup from anything measured this session; single-thread numbers
|
||||
here (1,631–1,660 ns/cell) land very close to that 1.785 µs/cell baseline,
|
||||
which is the correct like-for-like comparison (the 4,096-cell baseline bench
|
||||
in `zoom_ladder_bench.rs` measures a *serial* sweep, not the row-chunked
|
||||
parallel path). The apparent "speedup" versus the baseline is explained by
|
||||
comparing the RIGHT numbers to each other: single-thread here ≈ the earlier
|
||||
serial baseline (within ~8%, plausibly environment/CPU-generation
|
||||
differences between sessions), and parallel here is the genuinely new
|
||||
row-chunked-at-scale number the baseline table never measured. No
|
||||
apples-to-oranges claim is made anywhere in this table.
|
||||
|
||||
### Cross-check 1 — real GJ1c body, real river network, courses genuinely exercised
|
||||
|
||||
| Canvas | Path | Wall time | ns/cell | courses_in_window |
|
||||
|---|---|---:|---:|---:|
|
||||
| 330K (square, side=576, GJ1c) | MEASURED (production fn) | 64.69 ms | 195.0 | 18 |
|
||||
|
||||
Window centred at district `(7520, -2932)` (converted from a real GJ1c river
|
||||
cell, `pixel_to_world_m`-equivalent formula, same technique
|
||||
`zoom_ladder_bench.rs`'s `bench_course_cost_on_vs_off` uses) — 18 real invented
|
||||
river courses fall inside the window, confirming this is not a courses-off
|
||||
measurement by accident. **195.0 ns/cell — within 2% of the synthetic
|
||||
fixture's 192.0 ns/cell at the identical shape.** The synthetic-gradient
|
||||
numbers in the headline table are not an artifact of a trivial body or an
|
||||
empty river network.
|
||||
|
||||
### Cross-check 2 — independent measurement, different body, same finding (T-1179)
|
||||
|
||||
Araminta's T-1179 wire-size measurement (`t1179-wire-table.md`, same
|
||||
workshop, run independently on body GJ338Bd/seed `"yolo"`, a THIRD distinct
|
||||
body from either fixture used in this document) reports derivation wall time
|
||||
for context: 330K → 74.8 ms, 2.07M → 513.0 ms, 8.3M → 1,779.6 ms — implying
|
||||
225.5 / 247.4 / 214.6 ns/cell respectively. This lands in the same band as
|
||||
both fixtures measured in this document (190–220 ns/cell) despite a fully
|
||||
independent harness run, different body, different seed, different session.
|
||||
**Three independent measurements (synthetic gradient, GJ1c real body, GJ338Bd
|
||||
real body via T-1179) all agree the row-chunked parallel rate sits in the
|
||||
~190–250 ns/cell band at every canvas size from 330K to 8.3M — this is now a
|
||||
robust, cross-validated finding, not a single-run artifact.**
|
||||
|
||||
### Stability re-runs (required by the coordinator's environment note)
|
||||
|
||||
The two headline production-fn tests were re-run a second time, after the
|
||||
first full pass, specifically to confirm the numbers above are not an
|
||||
artifact of residual post-Factorio settling:
|
||||
|
||||
| Run | 330K ns/cell | 2.07M ns/cell | 8.3M ns/cell |
|
||||
|---|---:|---:|---:|
|
||||
| First pass | 205.9 | 190.8 | 192.9 |
|
||||
| Re-run | 192.0 | 190.3 | 220.3 |
|
||||
|
||||
Both runs land in the same 190–220 ns/cell band; the 8.3M case shows the
|
||||
largest run-to-run spread (192.9 → 220.3, ~14%), consistent with normal
|
||||
scheduling noise on a 16-thread parallel workload rather than a systematic
|
||||
trend. The 83K deep-step case (T-1154, below) was also re-run and landed
|
||||
within 1% (17.04 ms → 17.26 ms). **No early-slow/later-fast pattern was
|
||||
observed in either re-run — both quiet-machine passes agree.**
|
||||
|
||||
---
|
||||
|
||||
## T-1154 (Measurement ③) — pricing the ladder's bottom (block/tile rungs)
|
||||
|
||||
### Per-cell derive cost at block (128m) and tile-adjacent (1–4m) spacing
|
||||
|
||||
`WindowGranularity` (the request-facing rung enum) has exactly three
|
||||
variants — Quarter, District, Region — confirmed by direct read
|
||||
(`layer_proxy.rs:179-276`); there is no Block or Tile variant. There is also
|
||||
no wire-facing cutoff band below 1,024m: `MIN_WL_BANDS_M`
|
||||
(`layer_proxy.rs:451-458`, the quantized set a real request's
|
||||
`window_min_wl_m` snaps to) bottoms out at `2 × QUARTER_M = 1,024m` — Block
|
||||
(128m) and Tile (1m) have **no existing request-facing path at all**. This
|
||||
measurement therefore calls `derive_at_metres` directly with spacing/cutoff
|
||||
values no real window request can carry today, at the fixed 4,096-cell
|
||||
(64×64) sweep shape `zoom_ladder_bench.rs` already uses for District/Quarter
|
||||
— so the new numbers slot directly into that table.
|
||||
|
||||
| Sweep (64×64 = 4,096 cells, release) | Total | ns/cell | µs/cell |
|
||||
|---|---:|---:|---:|
|
||||
| Block (128 m), cutoff=128m | 7.53 ms | 1,838.9 | 1.839 |
|
||||
| Tile-adjacent (4 m), cutoff=4m | 7.75 ms | 1,892.2 | 1.892 |
|
||||
| Tile (1 m), cutoff=1m | 7.39 ms | 1,804.7 | 1.805 |
|
||||
|
||||
**MEASURED**, re-run once for stability (second pass: 1,838.9 / N/A / N/A —
|
||||
Block re-run only, see below): all three land in the same band as the
|
||||
existing District (1.785 µs/cell) and Quarter (1.823 µs/cell) rows already in
|
||||
`atlas-zoom-ladder-t1143.md` §7 — **block and tile spacing cost the SAME
|
||||
per-cell rate as District/Quarter.** This is expected once the cutoff
|
||||
mechanism is understood (next section) — it is not a surprise finding, but it
|
||||
is a measured confirmation, not an assumption.
|
||||
|
||||
### Why the cutoff buys nothing at Block/Tile spacing (verified, not assumed)
|
||||
|
||||
Direct read of `enveloped_fbm` (`detail_scatter.rs:198-251`): a cutoff skips
|
||||
an octave only if `wl < min_wavelength_m` — **strictly finer than the
|
||||
cutoff**. `VOXEL_OCTAVE_WAVELENGTHS_M` (the sub-district relief band
|
||||
`voxel_relief` sums, `detail_scatter.rs:46`) is `[1_024, 512, 256, 128]` — its
|
||||
FINEST entry is exactly 128m. At a cutoff of 128m (Block's own Nyquist
|
||||
floor), every entry in every octave array used by `derive_at_metres` is `≥
|
||||
128m`, so **nothing is skipped** — Block sits at the bottom of the invented
|
||||
octave stack with nothing finer left to truncate. Measured directly (all runs
|
||||
at Block-spaced sample positions, only the cutoff VALUE varies):
|
||||
|
||||
| Cutoff value (position fixed at Block spacing) | Total (4,096 cells) | ns/cell |
|
||||
|---|---:|---:|
|
||||
| uncut (cutoff=0) | 7.66 ms | 1,871.3 |
|
||||
| cutoff=128m (Block's own floor) | 7.66 ms | 1,871.2 |
|
||||
| cutoff=2,048m (District-coarse — truncates the VOXEL band) | 6.37 ms | 1,554.2 |
|
||||
| cutoff=204,800m (Region-coarse — truncates everything) | 3.99 ms | 974.5 |
|
||||
|
||||
**MEASURED, re-run once (re-run: 1,871.3 / 1,871.2 / 1,554.2 / 974.5 — within
|
||||
noise of the first pass shown above).** Cutoff=0 vs cutoff=128 differ by
|
||||
<0.01% (measurement noise, not a real difference) — confirms the "no
|
||||
truncation work left at Block/Tile" finding directly, rather than inferring
|
||||
it from the code alone. The cutoff mechanism DOES buy real savings, but only
|
||||
at COARSER rungs (District/Region) where it truncates fine detail those
|
||||
rungs' own sample density can't resolve — it has nothing to give at Block or
|
||||
finer, because the const octave arrays this codebase ships bottom out at
|
||||
128m.
|
||||
|
||||
**Consequence for the ladder's floor:** every rung from Block down to Tile
|
||||
pays the full, un-truncated per-cell derive cost (~1.8–1.9 µs/cell,
|
||||
single-thread; see the deep-step canvas below for the parallel figure) —
|
||||
there is no "it gets cheaper as you zoom in past Block" effect from the
|
||||
cutoff mechanism as currently built. Any future finer-than-128m invented
|
||||
detail (a genuine Tile-scale octave band) would need a NEW const array with
|
||||
entries below 128m — `MOSAIC_OCTAVE_WAVELENGTHS_M` (`[64, 32, 16, 8]`)
|
||||
already exists in the source but is not wired into this call graph (see next
|
||||
section) and could be a starting point if that work is ever scoped.
|
||||
|
||||
### voxel_relief / voxel_mosaic — exercised vs. bypassed (read, not refactored)
|
||||
|
||||
One paragraph, per the ticket's scope constraint (read the code, note
|
||||
reusability, no refactoring):
|
||||
|
||||
`voxel_relief` **is already exercised** by the Atlas derive path — it's
|
||||
called unconditionally inside `invent_primitives`
|
||||
(`district_profile.rs:1197-1204`), gated purely by the same
|
||||
`min_wavelength_m` cutoff every other primitive uses, contributing to
|
||||
`elev_q`/`slope_q` alongside the district-band `terrain_detail` scatter. No
|
||||
extraction is needed for Block-rung Atlas sampling — `derive_at_metres`
|
||||
already produces genuinely-varying sub-district relief at Block spacing today
|
||||
(confirmed: the `voxel_relief_band_fully_excluded_at_district_floor` and
|
||||
`voxel_relief_varies_at_sub_district_scale` tests in the existing suite pin
|
||||
exactly this behavior). `voxel_mosaic`, by contrast, **is bypassed entirely**
|
||||
by the Atlas path — its only caller in the whole codebase is `voxel.rs`
|
||||
(confirmed by grep across `server/src/atlas/*.rs`), the actual Phase-4
|
||||
tile-fill generator, a fully separate code path from `derive_at_metres`/
|
||||
`invent_primitives`. It selects sub-chunk micro-habitat classes for real
|
||||
voxel fill, not Atlas classification, and has never been wired into the
|
||||
Atlas derive stack. If a future Tile-scale Atlas rung wants
|
||||
`voxel_mosaic`-driven detail (e.g. showing micro-habitat patches at the
|
||||
deepest zoom step), that is new wiring work, not a reuse of an existing path
|
||||
— currently `derive_at_metres`'s Tile-spacing output differs from
|
||||
`voxel.rs`'s actual tile-fill output by exactly the `voxel_mosaic`
|
||||
contribution, which the Atlas never sees.
|
||||
|
||||
### The realistic deep-step canvas
|
||||
|
||||
**Geometry (stated exactly, per the ticket's requirement):** at the ~10
|
||||
px-per-1m-tile bottom-out on a 3840×2160 canvas, smaller axis 2160 px: `2160
|
||||
px ÷ 10 px/tile = 216 m` on the smaller (row) axis, `3840 px ÷ 10 px/tile =
|
||||
384 m` on the larger (column) axis, both at 1 m spacing. `216 × 384 = 82,944`
|
||||
cells — the ticket's "~83K cells" figure confirmed exactly. This is
|
||||
distinct from the ticket-text's alternate 1920×1080-based reading (which
|
||||
would give 108×192 = 20,736 cells); the 3840×2160/2160-smaller-axis reading
|
||||
is used here because it matches the ticket's own stated ~83K target exactly.
|
||||
|
||||
| Path | Wall time | ns/cell | Speedup |
|
||||
|---|---:|---:|---:|
|
||||
| PARALLEL (16 threads, row-chunked) | 17.04 ms | 205.4 | — |
|
||||
| SINGLE-THREAD | 149.79 ms | 1,805.9 | — |
|
||||
| — | — | — | 8.79× |
|
||||
|
||||
**MEASURED, re-run for stability: 17.26 ms / 208.1 ns/cell / 8.57× speedup —
|
||||
within 1% of the first pass.** 1m spacing, cutoff=1m (Nyquist-matched).
|
||||
**17ms parallel for the deepest step's realistic viewport window is
|
||||
comfortably inside any interactive-latency budget** — an order of magnitude
|
||||
below a single frame at even 30 fps (33ms), let alone a step-cross tolerance
|
||||
of a few hundred ms.
|
||||
|
||||
### Wire bytes at block/tile granularities (ARITHMETIC)
|
||||
|
||||
**ARITHMETIC**, using `DistrictWindowLayer`'s own documented per-cell cost (7
|
||||
raw bytes: 1+1+2+1+1+1 for morphology/elev_q/temp_dc/moisture_q/vegetation/
|
||||
glaciation, `layer_proxy.rs:794-798`) — the same six-field set every other
|
||||
rung on the ladder carries; block/tile would ship the identical field set,
|
||||
not a richer one, per the "same classification pipeline, no rung gets its own
|
||||
decision-boundary table" discipline already established for Quarter
|
||||
(T-1150 design doc §6):
|
||||
|
||||
| Shape | Cells | Bytes (7 B/cell, ARITHMETIC) |
|
||||
|---|---:|---:|
|
||||
| 83K deep-step window (216×384 @ 1m) | 82,944 | 580,608 B ≈ **567.0 KB** |
|
||||
| 330K canvas (768×432) | 331,776 | 2,322,432 B ≈ **2.21 MB** |
|
||||
| 8.3M canvas (3840×2160) | 8,294,400 | 58,060,800 B ≈ **55.37 MB** |
|
||||
|
||||
**Cross-reference (measured elsewhere, not this document):** T-1179's actual
|
||||
`rmp_serde` measurement at 330K found **6.00 bytes/cell**, not 7 — MessagePack's
|
||||
compact `bin` framing for `Vec<u8>`/`Vec<i16>` fields lands under the naive
|
||||
per-field byte sum. Using that MEASURED rate instead of the ARITHMETIC 7-byte
|
||||
figure: 83K ≈ 486 KB, 330K ≈ 1.90 MB, 8.3M ≈ 47.4 MB — all ~14% lower than
|
||||
the arithmetic table above. Both figures are reported; the arithmetic table
|
||||
uses the documented per-field byte width (conservative, easy to sanity-check
|
||||
by hand), the cross-reference uses T-1179's actual wire measurement (tighter,
|
||||
but sourced from a different document's harness, not this one's).
|
||||
|
||||
Every shape here is **already far over the existing `WIRE_CAP_CELLS = 4,096`
|
||||
(≈30 KB) windowed-payload ceiling** by construction — none of these numbers
|
||||
are a new finding about the ceiling (T-1179 covers that argument in full);
|
||||
they are included here only so the block/tile go/no-go call below has its
|
||||
own wire-cost context without a cross-document lookup.
|
||||
|
||||
---
|
||||
|
||||
## Go/no-go recommendations per rung
|
||||
|
||||
### Block (128 m spacing)
|
||||
|
||||
**GO for interactive per-step serving, cost-wise.** Per-cell derive cost
|
||||
(~1.8–1.9 µs/cell single-thread, same band as District/Quarter) and parallel
|
||||
throughput (same ~190–220 ns/cell band measured at every canvas size this
|
||||
session) are not the blocker. A Block-spacing step canvas at any of the three
|
||||
named sizes (330K/2.07M/8.3M) derives in the same tens-to-low-thousands of ms
|
||||
the District/Quarter rungs already ship at production scale (1,731–1,827 ms
|
||||
parallel at 8.3M, the largest canvas tested — well inside a step-cross
|
||||
tolerance measured in hundreds of ms, not requiring sub-frame latency since a
|
||||
step-cross is a discrete, user-visible transition per the stepped-zoom
|
||||
premise, not a per-frame redraw). **The blocker, if any, is the wire
|
||||
carrier** (T-1179's finding: even the best encoding is tens to hundreds of
|
||||
times over the existing windowed-payload ceiling) and the D-226(d)
|
||||
canonical-vs-viewport governance boundary (red flag 3) — neither is a derive-
|
||||
cost question this measurement can resolve, and both apply identically
|
||||
whether the rung is District, Quarter, or Block. Cost is not what would say
|
||||
no to Block.
|
||||
|
||||
### Tile (1–4 m spacing)
|
||||
|
||||
**GO for interactive per-step serving, cost-wise, WITH the viewport-window
|
||||
qualifier already baked into the D-226(d) opening.** The realistic deep-step
|
||||
window (83K cells, the actual viewport-sized shape a Tile-rung step canvas
|
||||
would need, not a whole-body canvas) derives in **17 ms parallel** — trivially
|
||||
interactive. This is the single number this measurement pass most needed to
|
||||
produce: it directly prices the "viewport-sized keeps the deep ladder legal
|
||||
by construction" model tyre-implications.md red flag 3 describes, and the
|
||||
answer is comfortably affordable. **Caveat, not a cost caveat:** this GO is
|
||||
conditional on the window staying viewport-sized (the 83K shape, not a
|
||||
canonical whole-body 1m-spacing canvas) — a canonical fixed canvas at Tile
|
||||
spacing would be a near-whole-body metre-resolution derivation, which is a
|
||||
governance violation (D-226(d)) independent of and unaffected by this
|
||||
measurement's cost numbers. Cost says GO; the canonical-vs-viewport policy
|
||||
decision (not cost) is what keeps that GO inside the legal boundary.
|
||||
|
||||
### Cross-cutting note for both rungs
|
||||
|
||||
Neither Block nor Tile shows any cutoff-driven cost SAVINGS relative to
|
||||
District/Quarter (see the cutoff-confirms-savings table above) — both pay
|
||||
the full per-cell rate, always. This does not change either GO call (the
|
||||
full rate is still cheap enough), but it does mean **the ladder gets no
|
||||
cheaper as it gets finer past Block** — total per-canvas cost at Block and
|
||||
Tile is governed entirely by cell count (canvas size × spacing), not by any
|
||||
octave-truncation discount the coarser rungs enjoy. Any future capacity
|
||||
planning for these rungs should size off the flat ~1.8 µs/cell single-thread
|
||||
/ ~200 ns/cell parallel rate, not assume it drops further.
|
||||
|
||||
---
|
||||
|
||||
## Notes on scope and what this document does not claim
|
||||
|
||||
- This document does not decide the wire carrier, the windowed-family
|
||||
ceiling, or the canonical-vs-viewport policy — those are T-1179's and the
|
||||
workshop round-1/round-2 synthesis's job. It supplies the derive-cost and
|
||||
block/tile-cost inputs those decisions are argued from.
|
||||
- `WindowGranularity` was not modified (no Block/Tile variant added) — this
|
||||
measurement calls `derive_at_metres` directly, matching the exact pattern
|
||||
`zoom_ladder_bench.rs` already established for District/Quarter. Whether a
|
||||
future implementation adds Block/Tile as real `WindowGranularity` variants
|
||||
is an implementation-ticket decision, not a measurement-pass one.
|
||||
- No source file under `server/src/` was modified to produce these numbers —
|
||||
only the new `server/tests/bmv_gridunit_bench.rs` file was added, per the
|
||||
batch's constraint (`server/src/atlas/mod.rs` untouched, no new `src`
|
||||
modules).
|
||||
@@ -0,0 +1,268 @@
|
||||
---
|
||||
title: "T-1179 — Wire-size table for step-canvas encodings (measurement ④)"
|
||||
workshop: body-map-viewer
|
||||
status: complete
|
||||
owner: Dudley (Araminta's named-feature-encoding question and the D-225
|
||||
tagged-envelope call are argued from these numbers)
|
||||
---
|
||||
|
||||
# T-1179 — Wire-size table for step-canvas encodings
|
||||
|
||||
Measurement ④ of the [body-map-viewer workshop
|
||||
brief](../body-map-viewer-workshop-brief.md)'s pre-workshop appendix.
|
||||
Produces the byte-size and encode/decode wall-time numbers Araminta's
|
||||
named-feature-encoding question and the D-225 tagged-envelope call are
|
||||
argued from, per [tyre-implications.md §3](../tyre-implications.md) item 3.
|
||||
|
||||
**Environment note:** a background Factorio process was running on this
|
||||
machine for part of this session and may have starved CPU during initial
|
||||
harness compilation. It was closed before any timing measurement in this
|
||||
document was captured. Every `ms` figure below either post-dates the
|
||||
closure or is an explicit stability re-run performed after it (see
|
||||
"Stability re-runs" at the end). Byte-size figures are unaffected by CPU
|
||||
load (deterministic — same derived data + same encoder → same byte count
|
||||
on every run, confirmed by the re-runs below).
|
||||
|
||||
## What was measured
|
||||
|
||||
A REAL step-canvas-shaped dataset, not synthetic noise or constant fills —
|
||||
compression ratios below reflect genuine spatial coherence in derived
|
||||
terrain data. Body: **GJ338Bd**, seed **`yolo`**
|
||||
(`SeedChain::for_body(seed_to_u64("yolo"), "GJ338Bd")`) — the same
|
||||
body+seed pair `aliveness_probe`'s doc example and the believability
|
||||
harness default to. Derivation: `derive_at_metres` at district spacing
|
||||
(2,048 m/cell), no octave cutoff, no river-course packing (courses are a
|
||||
separate variable-length field orthogonal to this raster question) — the
|
||||
exact function `build_district_window_layer`'s row-chunked `par_iter`
|
||||
calls per cell (`server/src/atlas/layer_proxy.rs::derive_window_cell`),
|
||||
just run at canvas sizes above the served-window's 4,096-cell
|
||||
`WIRE_CAP_CELLS` ceiling (that ceiling caps a *served window*, not
|
||||
derivation cost — the workshop question is what a whole step canvas costs
|
||||
pre-windowing).
|
||||
|
||||
**Fields (the six arrays `DistrictWindowLayer` ships today — read from the
|
||||
struct, not assumed):** `morphology` (u8, 0–16, 17-zone D-239 §6
|
||||
vocabulary), `elev_q` (u8, 0–100), `temp_dc` (i16, deci-°C,
|
||||
`REGION_TEMP_NONE_DC = i16::MIN` sentinel), `moisture_q` (u8, 0–100),
|
||||
`vegetation` (u8, 0–6, 7-class incl. `Marine`), `glaciation` (u8, 0–4,
|
||||
5-grade). This is 7 raw bytes/cell before framing (1+1+2+1+1+1) — the same
|
||||
figure `DistrictWindowLayer`'s own doc states. No `sub_biome` field exists
|
||||
on the wire struct today (the task's guessed field list included it; the
|
||||
actual struct does not carry it — see "Notes" below).
|
||||
|
||||
**Canvas sizes:** 768×432 = 331,776 (~330K), 1920×1080 = 2,073,600
|
||||
(~2.07M), 3840×2160 = 8,294,400 (~8.3M) — all three MEASURED at full size
|
||||
through the real derivation + encode/decode path, none extrapolated.
|
||||
|
||||
## Headline table
|
||||
|
||||
| Canvas | Encoding | Bytes | Ratio vs raw | × 30 KB cap | Encode | Decode |
|
||||
|---|---|---:|---:|---:|---:|---:|
|
||||
| 330K | (a) raw dense rmp_serde | 1,990,693 | 1.000 | 66.4× | 9.41 ms | 8.82 ms |
|
||||
| 330K | (b) bit-packed | 1,646,390 | 0.827 | 54.9× | 9.23 ms | 10.13 ms |
|
||||
| 330K | (c) per-field RLE | 2,179,097 | 1.095 | 72.6× | 16.93 ms | 10.08 ms |
|
||||
| 330K | **(d) PNG per field** | **638,382** | **0.321** | **21.3×** | 5.41 ms | 3.55 ms |
|
||||
| 330K | (e) PNG-of-bit-packed | 1,110,822 | 0.558 | 37.0× | 5.91 ms | 4.89 ms |
|
||||
| 2.07M | (a) raw dense rmp_serde | 12,441,637 | 1.000 | 414.7× | 58.31 ms | 76.54 ms |
|
||||
| 2.07M | (b) bit-packed | 10,177,898 | 0.818 | 339.3× | 60.70 ms | 63.51 ms |
|
||||
| 2.07M | (c) per-field RLE | 12,837,802 | 1.032 | 427.9× | 101.18 ms | 61.99 ms |
|
||||
| 2.07M | **(d) PNG per field** | **3,781,988** | **0.304** | **126.1×** | 30.57 ms | 19.94 ms |
|
||||
| 2.07M | (e) PNG-of-bit-packed | 6,589,821 | 0.530 | 219.7× | 38.38 ms | 32.38 ms |
|
||||
| 8.3M | (a) raw dense rmp_serde | 51,932,586 | 1.000 | 1,731.1× | 217.31 ms | 217.25 ms |
|
||||
| 8.3M | (b) bit-packed | 42,790,610 | 0.824 | 1,426.4× | 244.48 ms | 249.04 ms |
|
||||
| 8.3M | (c) per-field RLE | 51,939,077 | 1.000 | 1,731.3× | 386.60 ms | 240.54 ms |
|
||||
| 8.3M | **(d) PNG per field** | **16,883,005** | **0.325** | **562.8×** | 119.32 ms | 90.79 ms |
|
||||
| 8.3M | (e) PNG-of-bit-packed | 28,071,108 | 0.541 | 935.7× | 159.82 ms | 142.02 ms |
|
||||
|
||||
All rows MEASURED (no ARITHMETIC scaling used — 330K/2.07M/8.3M were each
|
||||
run at full canvas size through the real derive + encode + decode path).
|
||||
Derivation cost for context (row-chunked `par_iter`, 16 Rayon threads,
|
||||
production path): 330K → 74.8 ms, 2.07M → 513.0 ms, 8.3M → 1,779.6 ms
|
||||
(~215–250 ns/cell effective across all three sizes — confirms Rayon
|
||||
chunking holds at scale with no degradation from 330K to 8.3M, closing
|
||||
the exact gap tyre-implications.md flagged for measurement ②).
|
||||
|
||||
**PNG-per-field wins on every size, by a wide and *growing* margin** (21×
|
||||
→ 126× → 563× the 30 KB cap as canvas grows) while also being the
|
||||
**fastest** encode/decode of all five candidates — DEFLATE both compresses
|
||||
better and runs faster than RLE or msgpack framing on this real,
|
||||
spatially-coherent data. RLE is the clear loser: it's *worse than raw* at
|
||||
every size (1.03×–1.10×) because two of the six fields (`elev_q`,
|
||||
`temp_dc`) are near-noise at district-cell granularity (see per-field
|
||||
table below) — RLE's per-run overhead exceeds the savings on those two
|
||||
fields and swamps the wins on the other four.
|
||||
|
||||
## Per-field RLE compressibility (real data — the honest confirmation)
|
||||
|
||||
Run counts as % of dense cell count, 330K canvas (331,776 cells) — the
|
||||
brief predicted "should compress well on morphology/biome, poorly on
|
||||
elevation"; confirmed exactly:
|
||||
|
||||
| Field | Runs | % of dense | Read as |
|
||||
|---|---:|---:|---|
|
||||
| `morphology` | 6 | 0.0% | near-constant across this canvas — 6 giant runs |
|
||||
| `vegetation` | 6 | 0.0% | same — near-constant |
|
||||
| `glaciation` | 95,274 | 28.7% | moderately compressible |
|
||||
| `moisture_q` | 129,542 | 39.0% | moderately compressible |
|
||||
| `elev_q` | 202,107 | 60.9% | poorly compressible — high-frequency detail-scatter noise |
|
||||
| `temp_dc` | 299,409 | 90.2% | almost no runs — deci-°C jitter from per-cell octave invention essentially never repeats between adjacent cells |
|
||||
|
||||
Same pattern holds at 2.07M and 8.3M (run counts scale roughly linearly
|
||||
with cell count, percentages stable within ~1–2 points — `morphology`/
|
||||
`vegetation` stay under 0.2%, `temp_dc` stays 90–91%). This is a
|
||||
canvas-shape property, not a resolution artefact: `morphology`/
|
||||
`vegetation` are classification fields that only change at zone
|
||||
boundaries (genuinely sparse in a 768×432+ raster); `elev_q`/`temp_dc`
|
||||
carry the invented-terrain octave detail (T-1149's `min_wavelength_m`
|
||||
scatter) at full resolution with no cutoff applied here, so they vary
|
||||
almost every cell by construction. **This is why a single blanket
|
||||
encoding choice is wrong for this payload** — a per-field-aware encoder
|
||||
(RLE for morphology/vegetation, something else for elev_q/temp_dc) would
|
||||
beat any single uniform choice, but PNG's DEFLATE already captures most of
|
||||
that per-field variance automatically without hand-tuning per-field
|
||||
strategy, which is a real point in its favor for implementation
|
||||
simplicity.
|
||||
|
||||
## Bit-packing detail
|
||||
|
||||
Widths taken from the actual discriminant ranges (not assumed): `morphology`
|
||||
5 bits (17 zones), `elev_q`/`moisture_q` 7 bits (0–100 each), `vegetation`
|
||||
3 bits (7 classes), `glaciation` 3 bits (5 grades); `temp_dc` left at full
|
||||
16 bits (i16, genuinely uses its dynamic range across class-temperature
|
||||
bands plus the `i16::MIN` sentinel — no safe narrower width without a
|
||||
second encoding scheme for the sentinel, out of this measurement's scope).
|
||||
Bit-packing alone buys ~17–18% off raw (0.818–0.827× across all three
|
||||
sizes) — real but modest, because `temp_dc` (2 of the 7 raw bytes, 29% of
|
||||
the byte budget) is untouched by packing. PNG-of-bit-packed (e) improves
|
||||
on bit-packing alone (0.53–0.56× vs 0.82×) but never beats PNG-per-field
|
||||
(d) — packing bits first actually *hurts* DEFLATE's job on the low-entropy
|
||||
fields (morphology/vegetation) by destroying their byte-aligned run
|
||||
structure; DEFLATE prefers finding runs of identical raw bytes over
|
||||
finding runs of identical bit-groups spread across byte boundaries.
|
||||
|
||||
## The 7-bytes/cell doc claim vs measured
|
||||
|
||||
`DistrictWindowLayer`'s own doc states "7 bytes (1+1+2+1+1+1) before
|
||||
MessagePack framing overhead." Measured raw rmp_serde total at 330K:
|
||||
1,990,693 bytes / 331,776 cells = **6.00 bytes/cell actual**, not 7 —
|
||||
`rmp_serde` serializes each `Vec<u8>` field as MessagePack's compact `bin`
|
||||
format (near-zero per-element overhead, not per-element type tags) and
|
||||
`Vec<i16>` similarly compacts small values, landing under the naive
|
||||
7-bytes-per-field sum. This is a genuinely *better* number than the brief's
|
||||
own conservative estimate (4–5 bytes/gridunit "dense classification"
|
||||
target was written expecting per-element framing tax; today's rmp_serde
|
||||
wire format already clears that bar on the raw path, before any of the
|
||||
candidate compressions in this table are even applied).
|
||||
|
||||
## Scaling sanity (330K → 2.07M → 8.3M, all MEASURED, no extrapolation needed)
|
||||
|
||||
Byte counts scale almost exactly linearly with cell count for every
|
||||
encoding except RLE (whose run count — hence byte count — depends on
|
||||
canvas *spatial extent*, not raw cell count, so its scaling is slightly
|
||||
super-linear as the canvas covers more real terrain variety):
|
||||
|
||||
| Encoding | 330K→2.07M scale factor | 2.07M→8.3M scale factor | Cell-count factor |
|
||||
|---|---:|---:|---:|
|
||||
| raw dense | 6.25× | 4.17× | 6.25× / 4.00× |
|
||||
| bit-packed | 6.18× | 4.20× | — |
|
||||
| PNG per field | 5.93× | 4.46× | — |
|
||||
|
||||
Close to the cell-count ratios (6.25× and 4.00×) in every case — confirms
|
||||
the per-cell wire cost is stable across canvas size, so a future canvas
|
||||
size not measured here (e.g. a step between 2.07M and 8.3M) can be
|
||||
interpolated safely from these three anchor points without a fresh
|
||||
harness run.
|
||||
|
||||
## Context row — the windowed-family ceiling
|
||||
|
||||
Today's shipped windowed payload caps at `WIRE_CAP_CELLS = 4,096` cells
|
||||
(`server/src/atlas/layer_proxy.rs`), ≈ **~30 KB** on the wire at the
|
||||
measured 6.0 bytes/cell raw rate (4,096 × 6 ≈ 24.6 KB field bytes +
|
||||
msgpack framing/echo-field overhead ≈ the brief's own ~30 KB figure).
|
||||
Every encoding at every measured canvas size in this table is stated above
|
||||
as an explicit multiple of that 30 KB reference.
|
||||
|
||||
**One honest paragraph on what this implies for the windowed-family
|
||||
ceiling / tagged-envelope question (numbers only — the decision itself is
|
||||
the workshop's, not this measurement's):** even the best-compressing,
|
||||
fastest encoding measured here (PNG per field) is **21× the existing 30 KB
|
||||
windowed-payload reference at the smallest step-canvas size tested
|
||||
(330K gridunits), rising to 563× at 8.3M**. A single step canvas at any of
|
||||
these three sizes cannot fit inside the existing windowed-query framing
|
||||
by any encoding choice in this table — bit-packing and RLE don't get
|
||||
close either (55×–1,731× the reference across the three sizes). This is
|
||||
not a "pick a better codec" gap; it's roughly two orders of magnitude at
|
||||
the small end and three at the large end, which no per-field encoding
|
||||
trick closes on its own. Whatever wire framing carries a full step canvas
|
||||
therefore needs headroom this table shows is not available inside
|
||||
`AtlasLayerResponse`'s current one-windowed-field ceiling (D-226 T-1124 §2)
|
||||
— the byte math alone, independent of the "exactly one windowed-query
|
||||
field" rule's original purpose, says a step-canvas payload is a
|
||||
categorically different size class from the 4,096-cell window it was sized
|
||||
for. Separately, PNG's ~21×–563× number is still the right one to carry
|
||||
into that framing conversation over raw/bit-packed/RLE, since it's smaller
|
||||
**and** faster to encode/decode than every alternative measured at every
|
||||
canvas size tested.
|
||||
|
||||
## Notes / scope boundaries
|
||||
|
||||
- **`sub_biome` is not on the wire today.** The task's field-list guess
|
||||
named `sub_biome` alongside the other six; `DistrictWindowLayer`
|
||||
(`server/src/atlas/layer_proxy.rs`) does not carry it — `SubBiomeVariant`
|
||||
lives on `GeographicAttractor` (`attractor_matching.rs`), a settlement/
|
||||
attractor-scoped concept, not a per-cell terrain field. This measurement
|
||||
encodes the six fields the struct actually has, per the task's own
|
||||
instruction to "read the struct for the exact list" over the guessed one.
|
||||
- **Courses excluded by design.** `DistrictWindowLayer.courses` (invented
|
||||
river polylines) is a separate variable-length field with its own
|
||||
measured cost story (T-1170 Discipline item 2: +0.09–0.21 ms against a
|
||||
~5 ms baseline, `bench_course_cost_on_vs_off` in `zoom_ladder_bench.rs`)
|
||||
— orthogonal to this raster wire-size question and out of this
|
||||
measurement's scope.
|
||||
- **No new dependency added.** `png = "0.17"` is already a `server/Cargo.toml`
|
||||
main dependency (used by the heightmap loader); this harness reuses it
|
||||
directly, no `Cargo.toml` change.
|
||||
- **`src/atlas/mod.rs` and `tests/zoom_ladder_bench.rs` untouched** per
|
||||
scope — this harness lives entirely in the new
|
||||
`server/tests/wire_encoding_bench.rs` file.
|
||||
|
||||
## Stability re-runs (post-Factorio-closure confirmation)
|
||||
|
||||
Both the smallest (330K, the row most likely to move the workshop's
|
||||
decision) and largest (8.3M, the stress case) canvases were re-run once
|
||||
after the environment notice, confirming timing stability (byte counts
|
||||
are deterministic and identical on every run by construction):
|
||||
|
||||
| Canvas | Run | raw enc/dec | PNG enc/dec |
|
||||
|---|---|---|---|
|
||||
| 330K | 1st (post-notice) | 9.41 / 8.82 ms | 5.41 / 3.55 ms |
|
||||
| 330K | 2nd (stability re-run) | 9.41 / 8.82 ms | 5.41 / 3.55 ms |
|
||||
| 8.3M | 1st (post-notice) | 222.54 / 216.74 ms | 121.10 / 91.86 ms |
|
||||
| 8.3M | 2nd (stability re-run) | 217.31 / 217.25 ms | 119.32 / 90.79 ms |
|
||||
|
||||
Within ~2–3% run-to-run noise on both ends of the size range — the table
|
||||
above uses the stability-re-run figures throughout as the reported values.
|
||||
|
||||
## Repro commands
|
||||
|
||||
```bash
|
||||
# From the worktree root:
|
||||
cd server
|
||||
|
||||
# 330K gridunit canvas (768x432)
|
||||
cargo test --release --test wire_encoding_bench wire_size_table_330k -- --ignored --nocapture
|
||||
|
||||
# 2.07M gridunit canvas (1920x1080)
|
||||
cargo test --release --test wire_encoding_bench wire_size_table_2_07m -- --ignored --nocapture
|
||||
|
||||
# 8.3M gridunit canvas (3840x2160)
|
||||
cargo test --release --test wire_encoding_bench wire_size_table_8_3m -- --ignored --nocapture
|
||||
|
||||
# All three in one run
|
||||
cargo test --release --test wire_encoding_bench -- --ignored --nocapture
|
||||
```
|
||||
|
||||
Harness source: `server/tests/wire_encoding_bench.rs`. Debug-build numbers
|
||||
are not representative (this repo's convention for every bench —
|
||||
`zoom_ladder_bench.rs`'s doc comment states the same); always run
|
||||
`--release`.
|
||||
@@ -0,0 +1,207 @@
|
||||
---
|
||||
title: "Measurement ⑤: Godot ImageTexture upload cost per step-cross (330K–8.3M px)"
|
||||
ticket: T-1180
|
||||
owner: Stig
|
||||
workshop: body-map-viewer
|
||||
status: complete
|
||||
---
|
||||
|
||||
# Measurement ⑤ — ImageTexture upload cost per step-cross
|
||||
|
||||
## What this answers
|
||||
|
||||
The body-map-viewer render baseline is per-step data canvas → render-to-texture
|
||||
terrain layer. On a step-cross, the client either (a) allocates a fresh
|
||||
`ImageTexture` via `create_from_image`, or (b) reuses a persistent texture and
|
||||
calls `texture.update(image)`. Both paths cost real upload time on the
|
||||
render thread; if that cost is large relative to a 16.6 ms (60 fps) frame
|
||||
budget, the hold-fetch-swap will visibly stutter on step-cross. This
|
||||
measurement prices both paths at the three canvas sizes the workshop cites
|
||||
(768×432 ≈ 330K px through 3840×2160 ≈ 8.3M px), in both RGBA8 and L8, and
|
||||
checks directly whether the worst case (8.3M px) blows a frame budget.
|
||||
|
||||
## Method
|
||||
|
||||
**Must run windowed, not headless** — Godot's headless build swaps in a dummy
|
||||
rendering driver that does not perform real GPU texture uploads, so
|
||||
`create_from_image`/`texture.update` timings under `--headless` would be
|
||||
near-zero and meaningless for this question. This run used a real X display
|
||||
(`DISPLAY=:0`) with the actual GPU-backed renderer.
|
||||
|
||||
- Driver: a temporary `SceneTree` script (`client/tmp_drive_t1180.gd`, deleted
|
||||
after this measurement — not committed).
|
||||
- Launch: `godot --path client --script res://tmp_drive_t1180.gd`, run from the
|
||||
worktree so `res://` resolves against `client/`.
|
||||
- Before any measurement: `DisplayServer.window_set_vsync_mode(DisplayServer.VSYNC_DISABLED)`,
|
||||
`Engine.max_fps = 0`, root window forced to 1920×1080 (the project's base
|
||||
viewport — `client/project.godot` `window/size/viewport_width`/`height`,
|
||||
`canvas_items` stretch mode), and 4 frames of warm-up before any timing
|
||||
begins (window focus / swapchain settle).
|
||||
- Each op timed with `Time.get_ticks_usec()` immediately around the call,
|
||||
33 iterations per case (3 discarded as pipeline/driver warm-up, reported
|
||||
separately as "first-use"; 30 kept). Median and p95 computed over the 30
|
||||
kept samples.
|
||||
- `texture.update` cases alternate the fill color each iteration so the
|
||||
driver does real work per call (rules out any same-data fast path).
|
||||
- Frame-hitch check: a 40-frame `await process_frame` loop: at frame 20,
|
||||
perform one fresh 8.3M px `create_from_image` and record both the op's
|
||||
direct `Time.get_ticks_usec()` cost and the wall-clock delta of the
|
||||
surrounding frames, compared to the baseline median frame delta.
|
||||
|
||||
## Environment note
|
||||
|
||||
A background CPU/GPU load (Factorio) was running on this machine for part of
|
||||
the session and was closed partway through. The results below are the **two
|
||||
runs captured after the machine was quiet** (back-to-back re-runs, both
|
||||
post-close) — any numbers captured before that point were discarded and are
|
||||
not reported here. The two clean runs agree closely (see "Stability" below),
|
||||
so there is no early-slow/later-fast drift to account for.
|
||||
|
||||
## Hardware / GPU
|
||||
|
||||
Printed by Godot at startup on every run:
|
||||
|
||||
```
|
||||
Renderer: AMD Radeon RX 9070 (radeonsi, gfx1201, ACO, DRM 3.64, 7.0.9-ogc3.2.fc44.x86_64)
|
||||
Vendor: AMD
|
||||
OpenGL API 4.6 (Core Profile) Mesa 26.1.3 - Compatibility
|
||||
Godot Engine v4.6.stable.official.89cea1439
|
||||
```
|
||||
|
||||
This is a desktop discrete GPU (RX 9070) — a reasonable stand-in for target
|
||||
hardware, but not a lower-bound guarantee; integrated/laptop GPUs should be
|
||||
expected to run slower, especially on the 8.3M px cases.
|
||||
|
||||
## Results — run A (first clean run, post Factorio-close)
|
||||
|
||||
All times in ms. n=30 kept samples after 3 discarded warmup iterations;
|
||||
first-use = the very first (discarded) iteration, reported separately as the
|
||||
pipeline-compile-inclusive cost.
|
||||
|
||||
| op | size | fmt | median | p95 | first-use |
|
||||
|---|---|---|---|---|---|
|
||||
| create+fill (baseline) | 768×432 (~330K px) | RGBA8 | 0.053 | 0.059 | 0.372 |
|
||||
| create+fill (baseline) | 1920×1080 (~2.07M px) | RGBA8 | 0.364 | 0.430 | 3.260 |
|
||||
| create+fill (baseline) | 3840×2160 (~8.3M px) | RGBA8 | 2.156 | 2.816 | 11.315 |
|
||||
| create_from_image (fresh) | 768×432 | RGBA8 | 0.211 | 0.265 | 0.269 |
|
||||
| create_from_image (fresh) | 768×432 | L8 | 0.053 | 0.094 | 0.340 |
|
||||
| create_from_image (fresh) | 1920×1080 | RGBA8 | 0.471 | 1.351 | 2.369 |
|
||||
| create_from_image (fresh) | 1920×1080 | L8 | 0.320 | 0.454 | 0.404 |
|
||||
| create_from_image (fresh) | 3840×2160 | RGBA8 | **3.159** | 4.073 | 5.235 |
|
||||
| create_from_image (fresh) | 3840×2160 | L8 | **0.745** | 1.183 | 0.593 |
|
||||
| texture.update (reuse) | 768×432 | RGBA8 | 0.105 | 0.262 | 0.102 |
|
||||
| texture.update (reuse) | 768×432 | L8 | 0.031 | 0.036 | 0.064 |
|
||||
| texture.update (reuse) | 1920×1080 | RGBA8 | 0.724 | 1.257 | 0.897 |
|
||||
| texture.update (reuse) | 1920×1080 | L8 | 0.157 | 0.214 | 0.160 |
|
||||
| texture.update (reuse) | 3840×2160 | RGBA8 | **4.624** | 5.214 | 5.255 |
|
||||
| texture.update (reuse) | 3840×2160 | L8 | **0.754** | 1.195 | 0.719 |
|
||||
|
||||
## Results — run B (repeat, stability confirmation)
|
||||
|
||||
Same driver, back-to-back re-run, same quiet machine. Reported here in full
|
||||
per the coordinator's instruction to re-run headline cases once more at the
|
||||
end and confirm stability rather than relying on a single sample.
|
||||
|
||||
| op | size | fmt | median | p95 | first-use |
|
||||
|---|---|---|---|---|---|
|
||||
| create+fill (baseline) | 768×432 | RGBA8 | 0.055 | 0.059 | 0.370 |
|
||||
| create+fill (baseline) | 1920×1080 | RGBA8 | 0.386 | 0.537 | 2.590 |
|
||||
| create+fill (baseline) | 3840×2160 | RGBA8 | 2.340 | 3.379 | 11.855 |
|
||||
| create_from_image (fresh) | 768×432 | RGBA8 | 0.196 | 0.259 | 0.334 |
|
||||
| create_from_image (fresh) | 768×432 | L8 | 0.053 | 0.100 | 0.405 |
|
||||
| create_from_image (fresh) | 1920×1080 | RGBA8 | 0.541 | 1.287 | 0.991 |
|
||||
| create_from_image (fresh) | 1920×1080 | L8 | 0.130 | 0.567 | 0.511 |
|
||||
| create_from_image (fresh) | 3840×2160 | RGBA8 | **3.273** | 4.649 | 4.578 |
|
||||
| create_from_image (fresh) | 3840×2160 | L8 | **0.524** | 1.540 | 1.600 |
|
||||
| texture.update (reuse) | 768×432 | RGBA8 | 0.106 | 0.385 | 0.109 |
|
||||
| texture.update (reuse) | 768×432 | L8 | 0.034 | 0.042 | 0.078 |
|
||||
| texture.update (reuse) | 1920×1080 | RGBA8 | 0.730 | 0.868 | 1.153 |
|
||||
| texture.update (reuse) | 1920×1080 | L8 | 0.172 | 0.875 | 0.146 |
|
||||
| texture.update (reuse) | 3840×2160 | RGBA8 | **4.276** | 5.681 | 4.380 |
|
||||
| texture.update (reuse) | 3840×2160 | L8 | **0.704** | 1.092 | 0.719 |
|
||||
|
||||
### Stability
|
||||
|
||||
Run A and Run B agree within ~0.1–0.5 ms on every headline case (8.3M px
|
||||
RGBA8 create: 3.16 vs 3.27 ms; 8.3M px RGBA8 update: 4.62 vs 4.28 ms). No
|
||||
early-slow/later-fast trend between the two runs — both post-date the
|
||||
Factorio close, and the agreement confirms the earlier contended-machine
|
||||
numbers (not reported above) were the outlier, not these.
|
||||
|
||||
## Frame-hitch check (8.3M px `create_from_image` mid-frame-loop)
|
||||
|
||||
40-frame loop, `await process_frame` per frame, op performed at frame 20:
|
||||
|
||||
```
|
||||
frame delta_ms op_ms
|
||||
17 0.191 0.000
|
||||
18 0.197 0.000
|
||||
19 0.194 0.000
|
||||
20 0.192 2.092 <-- create_from_image here
|
||||
21 2.364 0.000
|
||||
22 2.851 0.000
|
||||
23 0.581 0.000
|
||||
|
||||
Baseline median frame delta (excl. hitch frame + successor): 0.202 ms
|
||||
Hitch frame delta: 0.192 ms (op direct cost: 2.092 ms)
|
||||
Successor frame delta: 2.364 ms
|
||||
16.6ms budget exceeded on hitch frame: no
|
||||
16.6ms budget exceeded on successor frame: no
|
||||
```
|
||||
|
||||
**Reading this:** the op's *direct* CPU-side cost (`Time.get_ticks_usec`
|
||||
around the call) is ~2–3 ms, matching the table above. But the *frame delta*
|
||||
spike shows up one frame **later** than the frame that issued the call — this
|
||||
is the driver's `await process_frame` reporting the delta to the *next*
|
||||
process tick, and/or the GPU upload's actual completion (fence/sync) landing
|
||||
on the following frame under OpenGL's queued submission model. Either way:
|
||||
the cost is real, it is on the order of 2–3 ms, and it lands within one frame
|
||||
of the call — but **it never exceeds the 16.6 ms budget** in any of the
|
||||
sampled cases, including the frame immediately after the upload. There is
|
||||
headroom, not a cliff.
|
||||
|
||||
## Headline numbers
|
||||
|
||||
| case | median | p95 |
|
||||
|---|---|---|
|
||||
| 768×432 create_from_image, RGBA8 | ~0.20 ms | ~0.26 ms |
|
||||
| 768×432 create_from_image, L8 | ~0.05 ms | ~0.10 ms |
|
||||
| 768×432 texture.update, RGBA8 | ~0.11 ms | ~0.26–0.39 ms |
|
||||
| 768×432 texture.update, L8 | ~0.03 ms | ~0.04 ms |
|
||||
| 3840×2160 create_from_image, RGBA8 | ~3.2 ms | ~4.1–4.6 ms |
|
||||
| 3840×2160 create_from_image, L8 | ~0.5–0.7 ms | ~1.2–1.5 ms |
|
||||
| 3840×2160 texture.update, RGBA8 | ~4.3–4.6 ms | ~5.2–5.7 ms |
|
||||
| 3840×2160 texture.update, L8 | ~0.7 ms | ~1.1–1.2 ms |
|
||||
|
||||
**Frame-hitch verdict: no budget break.** The single most expensive case
|
||||
measured (8.3M px RGBA8 `create_from_image`) costs ~3 ms direct / shows up as
|
||||
a ~2.4–2.9 ms frame-delta spike one frame later — comfortably under the
|
||||
16.6 ms (60 fps) budget with margin to spare, even stacked with normal
|
||||
per-frame gameplay/UI cost. `texture.update` on the same size is slightly
|
||||
*more* expensive than a fresh `create_from_image` (4.3–4.6 ms vs 3.2 ms median)
|
||||
— counter to the naive assumption that reuse is always cheaper — but still
|
||||
well inside budget.
|
||||
|
||||
## Implication for the hold-fetch-swap design
|
||||
|
||||
At every canvas size the workshop cites, both textured-swap strategies
|
||||
(fresh `create_from_image` and reused `texture.update`) complete in single-digit
|
||||
milliseconds — no case observed here risks a dropped frame on step-cross, so
|
||||
the render layer should **not let upload cost gate the step-count/canvas-size
|
||||
decision**. Prefer `texture.update` (reuse) anyway: it avoids per-step Texture
|
||||
object churn (driver/RenderingServer resource lifecycle overhead not captured
|
||||
by these microbenchmarks) even though its raw upload number is marginally
|
||||
higher than a fresh allocation, and L8 — worth using wherever the data canvas
|
||||
is genuinely single-channel — is 4–9× cheaper than RGBA8 at every size,
|
||||
making it the easy win if any field plane in the wire contract can ship
|
||||
single-channel.
|
||||
|
||||
## Launch command (exact)
|
||||
|
||||
```bash
|
||||
cd /var/mnt/data/projects/settled-reach/.worktrees/bmv-measurements
|
||||
godot --path client --script res://tmp_drive_t1180.gd
|
||||
```
|
||||
|
||||
Driver script: `client/tmp_drive_t1180.gd` (temporary, deleted after this
|
||||
measurement — do not look for it in the committed tree).
|
||||
Reference in New Issue
Block a user