jpmschweitzerandClaude Opus 4.7
f3e017a12f
Pre-push surfaced fmt + clippy (-D warnings) failures in the new code: - rustfmt the 6 new/changed atlas files + the bench example. - features.rs: HashMap → BTreeMap (project bans HashMap for determinism via clippy disallowed_types; the bucket map is lookup-only either way). - attractor_matching.rs: drop now-redundant .clone() on AttractorType (it became Copy in #953) — clippy clone_on_copy. - drainage.rs tests: manual range → (1..=12).contains(&n). - features.rs test: drop .clone() on Copy AttractorType. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
726 lines
24 KiB
Rust
726 lines
24 KiB
Rust
//! D8 drainage routing — flow direction, flow accumulation, river network
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//! extraction, and drainage basin delineation (D-208).
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//!
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//! **Determinism (D-010, D-208):** All flow-direction comparisons use integer
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//! arithmetic on scaled elevation values (`(elev * 1_000_000.0) as i64`) to
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//! avoid f32 comparison non-determinism. Tie-breaking uses a fixed D8 neighbor
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//! priority order. The result is bit-identical across runs on the same inputs.
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//!
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//! **Algorithm:**
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//! 1. Scale f32 elevation to i64 integers.
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//! 2. Priority-flood depression fill (iterative, convergence in ≤10 passes).
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//! 3. D8 flow direction: steepest descent, 8-neighbor, wraps horizontally.
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//! 4. Flow accumulation via topological sort of the D8 DAG.
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//! 5. River network extraction: cells with accumulation > RIVER_THRESHOLD.
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//! 6. Basin labeling: flood-fill seeded at pour points.
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//!
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//! The grid is row-major. Row 0 is the north pole; row H-1 is the south pole.
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//! Columns wrap horizontally (the globe is equirectangular).
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use std::collections::VecDeque;
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use crate::atlas::body_world_state::{DrainageBasin, RiverNetwork};
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/// A cell is a river cell when its flow accumulation exceeds this threshold (D-208).
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pub const RIVER_THRESHOLD: i32 = 200;
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/// Scale factor for converting f32 elevation to integer for deterministic comparison.
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const ELEV_SCALE: f64 = 1_000_000.0;
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// D8 neighbor offsets (dr, dc) in fixed priority order for deterministic tie-breaking.
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// Priority: cardinal directions first (N, S, E, W), then diagonals (NE, NW, SE, SW).
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const D8: [(i32, i32); 8] = [
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(-1, 0), // N
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(1, 0), // S
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(0, 1), // E
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(0, -1), // W
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(-1, 1), // NE
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(-1, -1), // NW
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(1, 1), // SE
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(1, -1), // SW
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];
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/// Result of the full D8 drainage analysis for one body.
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#[derive(Debug, Clone)]
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pub struct DrainageResult {
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pub river_network: RiverNetwork,
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pub drainage_basins: Vec<DrainageBasin>,
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/// Per-cell flow accumulation (row-major, `w × h`): the upstream cell count
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/// draining through each cell. Exposed for D-209 attractor-strength
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/// normalization (`flow_accumulation[cell] / max_accumulation`).
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pub flow_accumulation: Vec<i32>,
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/// Maximum flow accumulation across the grid — the denominator for
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/// normalized attractor strength (D-209). Always ≥ 1.
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pub max_accumulation: i32,
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}
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// ---------------------------------------------------------------------------
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// Public entry point
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// ---------------------------------------------------------------------------
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/// Run the full D8 drainage analysis on an elevation grid.
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///
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/// `elevation` is a row-major float32 grid of shape `height × width`, values
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/// in [0.0, 1.0]. `sea_level` is the fraction below which terrain is ocean.
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///
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/// Returns `DrainageResult` with the river network and drainage basins.
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pub fn analyze(elevation: &[f32], width: u32, height: u32, sea_level: f32) -> DrainageResult {
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let w = width as usize;
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let h = height as usize;
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// 1. Scale to integers.
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let scaled: Vec<i64> = elevation
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.iter()
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.map(|&e| (e as f64 * ELEV_SCALE) as i64)
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.collect();
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// 2. Depression fill.
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let filled = depression_fill(&scaled, w, h);
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// 3. D8 flow direction. -1 = no outflow (edge or flat peak).
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let fdir = flow_direction(&filled, w, h);
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// 4. Flow accumulation.
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let accum = flow_accumulation(&fdir, w, h);
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// 5. River network.
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let river_network = extract_river_network(&accum, &fdir, w, h, sea_level, elevation);
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// 6. Basin labeling.
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let labels = label_basins(&fdir, &accum, w, h);
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// 7. Merge small basins + clamp count to [4, 12].
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let labels = merge_small_basins(labels, w, h, 4, 12);
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// 8. Build DrainageBasin structs.
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let drainage_basins = build_basins(&labels, w, h);
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// Max accumulation for D-209 strength normalization (clamped ≥ 1 so the
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// division is always well-defined, even on a flat/empty world).
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let max_accumulation = accum.iter().copied().max().unwrap_or(1).max(1);
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DrainageResult {
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river_network,
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drainage_basins,
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flow_accumulation: accum,
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max_accumulation,
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}
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}
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// ---------------------------------------------------------------------------
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// Step 2: Depression fill
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// ---------------------------------------------------------------------------
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fn depression_fill(scaled: &[i64], w: usize, h: usize) -> Vec<i64> {
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let mut filled = scaled.to_vec();
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for _ in 0..10 {
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let mut changed = false;
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for r in 1..h.saturating_sub(1) {
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for c in 0..w {
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let mut nbr_min = i64::MAX;
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for &(dr, dc) in &D8 {
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let nr = r as i32 + dr;
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let nc = (c as i32 + dc).rem_euclid(w as i32) as usize;
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if nr >= 0 && nr < h as i32 {
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let val = filled[nr as usize * w + nc];
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if val < nbr_min {
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nbr_min = val;
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}
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}
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}
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if filled[r * w + c] < nbr_min {
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filled[r * w + c] = nbr_min + 1;
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changed = true;
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}
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}
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}
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if !changed {
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break;
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}
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}
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filled
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}
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// ---------------------------------------------------------------------------
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// Step 3: D8 flow direction
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// ---------------------------------------------------------------------------
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/// Returns per-cell flow direction index into D8 (0–7), or -1 for no outflow.
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fn flow_direction(filled: &[i64], w: usize, h: usize) -> Vec<i8> {
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let mut fdir = vec![-1i8; w * h];
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for r in 0..h {
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for c in 0..w {
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let elev = filled[r * w + c];
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let mut best_drop = 0i64;
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let mut best_k: i8 = -1;
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for (k, &(dr, dc)) in D8.iter().enumerate() {
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let nr = r as i32 + dr;
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let nc = (c as i32 + dc).rem_euclid(w as i32) as usize;
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if nr < 0 || nr >= h as i32 {
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continue;
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}
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let drop = elev - filled[nr as usize * w + nc];
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if drop > best_drop {
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best_drop = drop;
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best_k = k as i8;
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}
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}
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fdir[r * w + c] = best_k;
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}
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}
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fdir
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}
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// ---------------------------------------------------------------------------
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// Step 4: Flow accumulation
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// ---------------------------------------------------------------------------
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fn flow_accumulation(fdir: &[i8], w: usize, h: usize) -> Vec<i32> {
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let n = w * h;
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let mut in_degree = vec![0i32; n];
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for r in 0..h {
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for c in 0..w {
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let k = fdir[r * w + c];
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if k < 0 {
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continue;
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}
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let (dr, dc) = D8[k as usize];
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let nr = r as i32 + dr;
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let nc = (c as i32 + dc).rem_euclid(w as i32) as usize;
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if nr >= 0 && nr < h as i32 {
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in_degree[nr as usize * w + nc] += 1;
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}
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}
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}
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let mut queue = VecDeque::new();
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for (i, °) in in_degree.iter().enumerate().take(n) {
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if deg == 0 {
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queue.push_back(i);
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}
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}
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let mut accum = vec![1i32; n];
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while let Some(idx) = queue.pop_front() {
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let r = idx / w;
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let c = idx % w;
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let k = fdir[idx];
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if k < 0 {
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continue;
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}
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let (dr, dc) = D8[k as usize];
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let nr = r as i32 + dr;
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let nc = (c as i32 + dc).rem_euclid(w as i32) as usize;
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if nr >= 0 && nr < h as i32 {
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let ni = nr as usize * w + nc;
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accum[ni] += accum[idx];
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in_degree[ni] -= 1;
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if in_degree[ni] == 0 {
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queue.push_back(ni);
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}
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}
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}
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accum
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}
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// ---------------------------------------------------------------------------
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// Step 5: River network extraction
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// ---------------------------------------------------------------------------
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fn extract_river_network(
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accum: &[i32],
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fdir: &[i8],
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w: usize,
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h: usize,
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sea_level: f32,
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elevation: &[f32],
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) -> RiverNetwork {
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let n = w * h;
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// River cells: above threshold AND above sea level.
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let is_river: Vec<bool> = (0..n)
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.map(|i| accum[i] > RIVER_THRESHOLD && elevation[i] >= sea_level)
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.collect();
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let river_cells: Vec<(u16, u16)> = (0..n)
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.filter(|&i| is_river[i])
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.map(|i| ((i / w) as u16, (i % w) as u16))
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.collect();
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// Confluences: river cells with 2+ river neighbors flowing into them.
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let mut inflow_count = vec![0u8; n];
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for r in 0..h {
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for c in 0..w {
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let i = r * w + c;
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if !is_river[i] {
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continue;
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}
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let k = fdir[i];
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if k < 0 {
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continue;
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}
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let (dr, dc) = D8[k as usize];
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let nr = r as i32 + dr;
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let nc = (c as i32 + dc).rem_euclid(w as i32) as usize;
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if nr >= 0 && nr < h as i32 {
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let ni = nr as usize * w + nc;
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if is_river[ni] {
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inflow_count[ni] = inflow_count[ni].saturating_add(1);
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}
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}
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}
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}
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let confluences: Vec<(u16, u16)> = (0..n)
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.filter(|&i| is_river[i] && inflow_count[i] >= 2)
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.map(|i| ((i / w) as u16, (i % w) as u16))
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.collect();
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// Mouths: river cells that flow to a sea cell or to the polar edge.
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let mouths: Vec<(u16, u16)> = (0..n)
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.filter(|&i| {
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if !is_river[i] {
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return false;
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}
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let r = i / w;
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let c = i % w;
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let k = fdir[i];
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if k < 0 {
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return true; // no outflow — edge
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}
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let (dr, dc) = D8[k as usize];
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let nr = r as i32 + dr;
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let nc = (c as i32 + dc).rem_euclid(w as i32) as usize;
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if nr < 0 || nr >= h as i32 {
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return true; // polar edge
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}
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// Flows into a sub-sea-level cell = mouth
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elevation[nr as usize * w + nc] < sea_level
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})
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.map(|i| ((i / w) as u16, (i % w) as u16))
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.collect();
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RiverNetwork {
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river_cells,
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confluences,
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mouths,
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}
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}
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// ---------------------------------------------------------------------------
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// Step 6: Basin labeling
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// ---------------------------------------------------------------------------
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fn label_basins(fdir: &[i8], accum: &[i32], w: usize, h: usize) -> Vec<i32> {
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let n = w * h;
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let mut labels = vec![-1i32; n];
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// Pour points: local accumulation maxima above river threshold.
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let mut pour_pts: Vec<usize> = Vec::new();
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for i in 0..n {
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if accum[i] <= RIVER_THRESHOLD {
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continue;
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}
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let r = i / w;
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let c = i % w;
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let mut is_max = true;
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for &(dr, dc) in &D8 {
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let nr = r as i32 + dr;
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let nc = (c as i32 + dc).rem_euclid(w as i32) as usize;
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if nr >= 0 && nr < h as i32 && accum[nr as usize * w + nc] > accum[i] {
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is_max = false;
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break;
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}
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}
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if is_max {
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pour_pts.push(i);
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}
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}
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if pour_pts.is_empty() {
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// Flat/ocean world — single basin.
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labels.iter_mut().for_each(|l| *l = 0);
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return labels;
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}
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for (basin_id, &idx) in pour_pts.iter().enumerate() {
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labels[idx] = basin_id as i32;
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}
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// Trace remaining cells: follow fdir until a labeled cell is reached.
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for start in 0..n {
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if labels[start] >= 0 {
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continue;
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}
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// Walk forward, accumulate path.
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let mut path: Vec<usize> = Vec::new();
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let mut cur = start;
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let label = loop {
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if labels[cur] >= 0 {
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break labels[cur];
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}
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path.push(cur);
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let k = fdir[cur];
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if k < 0 {
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break 0; // no outflow — assign to basin 0
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}
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let r = cur / w;
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let c = cur % w;
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let (dr, dc) = D8[k as usize];
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let nr = r as i32 + dr;
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let nc = (c as i32 + dc).rem_euclid(w as i32) as usize;
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if nr < 0 || nr >= h as i32 {
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break 0; // polar edge
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}
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let next = nr as usize * w + nc;
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// Cycle guard: if we're visiting a cell already in path, stop.
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if path.contains(&next) {
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break 0;
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}
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cur = next;
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};
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for idx in path {
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labels[idx] = label;
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}
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}
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labels
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}
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// ---------------------------------------------------------------------------
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// Step 7: Merge small basins
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// ---------------------------------------------------------------------------
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/// Union-find root with path compression.
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fn uf_find(parent: &mut [i32], x: i32) -> i32 {
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let mut root = x;
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while parent[root as usize] != root {
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root = parent[root as usize];
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}
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let mut cur = x;
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while parent[cur as usize] != root {
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let next = parent[cur as usize];
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parent[cur as usize] = root;
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cur = next;
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}
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root
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}
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/// Merge small basins into their largest neighbor until the count is in
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/// `[min_count, max_count]` and every basin holds ≥ 2% of the surface.
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///
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/// Builds a basin adjacency graph + sizes in a single grid pass, then performs
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/// all merges as union-find operations on that graph — the grid is rewritten
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/// exactly once at the end. This replaces the former O(merges × n) loop (which
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/// rescanned the whole grid per merge: ~250ms at 512×256) with O(n + merges).
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/// Determinism: smallest basin chosen by `(size, id)`, largest neighbor by
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/// `(size, then lowest id)` — both fixed orders.
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fn merge_small_basins(
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mut labels: Vec<i32>,
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w: usize,
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h: usize,
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min_count: usize,
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max_count: usize,
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) -> Vec<i32> {
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use std::collections::BTreeSet;
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let n = w * h;
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let min_frac = 0.02f64; // 2% minimum basin area
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let max_label = labels.iter().copied().max().unwrap_or(0);
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let nb = (max_label + 1) as usize;
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if nb <= 1 {
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return labels; // single basin — nothing to merge
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}
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// One pass: basin sizes + adjacency (neighbor labels per basin).
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let mut size = vec![0usize; nb];
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let mut adj: Vec<BTreeSet<i32>> = vec![BTreeSet::new(); nb];
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for r in 0..h {
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for c in 0..w {
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let l = labels[r * w + c];
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size[l as usize] += 1;
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for &(dr, dc) in &D8 {
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let nr = r as i32 + dr;
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let nc = (c as i32 + dc).rem_euclid(w as i32) as usize;
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if nr >= 0 && nr < h as i32 {
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let nl = labels[nr as usize * w + nc];
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if nl != l {
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adj[l as usize].insert(nl);
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}
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}
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}
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}
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}
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let mut parent: Vec<i32> = (0..nb as i32).collect();
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let mut active: BTreeSet<i32> = (0..nb as i32).collect();
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while active.len() > min_count {
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// Smallest active basin (tie → lowest id; BTreeSet iterates ascending).
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let smallest = *active
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.iter()
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.min_by_key(|&&b| (size[b as usize], b))
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.unwrap();
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let smallest_size = size[smallest as usize];
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if active.len() <= max_count && smallest_size as f64 / n as f64 >= min_frac {
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break;
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}
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// Largest active neighbor (tie → lowest id).
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let mut best: i32 = -1;
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let mut best_size = 0usize;
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for &nb_lbl in &adj[smallest as usize] {
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let rep = uf_find(&mut parent, nb_lbl);
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if rep == smallest {
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continue;
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}
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let s = size[rep as usize];
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if s > best_size || (s == best_size && (best < 0 || rep < best)) {
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best_size = s;
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best = rep;
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}
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}
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// No neighbor (isolated basin) → merge into the next smallest active.
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let merge_into = if best >= 0 {
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best
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} else {
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match active.iter().find(|&&b| b != smallest) {
|
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Some(&other) => other,
|
||
None => break,
|
||
}
|
||
};
|
||
|
||
// Union smallest → merge_into; fold size and adjacency.
|
||
parent[smallest as usize] = merge_into;
|
||
size[merge_into as usize] += smallest_size;
|
||
let small_adj = std::mem::take(&mut adj[smallest as usize]);
|
||
for nb_lbl in small_adj {
|
||
let rep = uf_find(&mut parent, nb_lbl);
|
||
if rep != merge_into {
|
||
adj[merge_into as usize].insert(rep);
|
||
}
|
||
}
|
||
active.remove(&smallest);
|
||
}
|
||
|
||
// Resolve every cell to its basin representative (single pass).
|
||
for l in labels.iter_mut() {
|
||
*l = uf_find(&mut parent, *l);
|
||
}
|
||
|
||
// Renumber contiguously from 0.
|
||
let unique: BTreeSet<i32> = labels.iter().copied().collect();
|
||
let remap: std::collections::BTreeMap<i32, i32> = unique
|
||
.iter()
|
||
.enumerate()
|
||
.map(|(new, &old)| (old, new as i32))
|
||
.collect();
|
||
for l in labels.iter_mut() {
|
||
*l = remap[l];
|
||
}
|
||
|
||
labels
|
||
}
|
||
|
||
// ---------------------------------------------------------------------------
|
||
// Step 8: Build DrainageBasin structs
|
||
// ---------------------------------------------------------------------------
|
||
|
||
fn build_basins(labels: &[i32], w: usize, h: usize) -> Vec<DrainageBasin> {
|
||
let n = w * h;
|
||
let mut basin_map: std::collections::BTreeMap<i32, Vec<usize>> =
|
||
std::collections::BTreeMap::new();
|
||
|
||
for (i, &l) in labels.iter().enumerate() {
|
||
basin_map.entry(l).or_default().push(i);
|
||
}
|
||
|
||
let mut basins: Vec<DrainageBasin> = Vec::with_capacity(basin_map.len());
|
||
let mut ids: Vec<i32> = basin_map.keys().copied().collect();
|
||
ids.sort();
|
||
|
||
for basin_id in ids {
|
||
let cells = &basin_map[&basin_id];
|
||
let area_pct = cells.len() as f32 / n as f32;
|
||
|
||
// Boundary cells: in this basin, adjacent to a different basin or edge.
|
||
let mut boundary: Vec<(u16, u16)> = Vec::new();
|
||
for &idx in cells {
|
||
let r = idx / w;
|
||
let c = idx % w;
|
||
let mut on_boundary = false;
|
||
for &(dr, dc) in &D8 {
|
||
let nr = r as i32 + dr;
|
||
let nc = (c as i32 + dc).rem_euclid(w as i32) as usize;
|
||
if nr < 0 || nr >= h as i32 {
|
||
on_boundary = true;
|
||
break;
|
||
}
|
||
if labels[nr as usize * w + nc] != basin_id {
|
||
on_boundary = true;
|
||
break;
|
||
}
|
||
}
|
||
if on_boundary {
|
||
boundary.push((r as u16, c as u16));
|
||
}
|
||
}
|
||
|
||
// Sort boundary by angle from centroid for a coherent polygon.
|
||
if !boundary.is_empty() {
|
||
let cr = boundary.iter().map(|&(r, _)| r as f32).sum::<f32>() / boundary.len() as f32;
|
||
let cc = boundary.iter().map(|&(_, c)| c as f32).sum::<f32>() / boundary.len() as f32;
|
||
boundary.sort_by(|&(r1, c1), &(r2, c2)| {
|
||
let a1 = (r1 as f32 - cr).atan2(c1 as f32 - cc);
|
||
let a2 = (r2 as f32 - cr).atan2(c2 as f32 - cc);
|
||
a1.partial_cmp(&a2).unwrap_or(std::cmp::Ordering::Equal)
|
||
});
|
||
// Subsample to ≤500 points.
|
||
if boundary.len() > 500 {
|
||
let step = boundary.len() / 500;
|
||
boundary = boundary.into_iter().step_by(step).collect();
|
||
}
|
||
}
|
||
|
||
basins.push(DrainageBasin {
|
||
basin_id: basin_id as u32,
|
||
boundary,
|
||
area_pct,
|
||
});
|
||
}
|
||
|
||
basins
|
||
}
|
||
|
||
// ---------------------------------------------------------------------------
|
||
// Tests
|
||
// ---------------------------------------------------------------------------
|
||
|
||
#[cfg(test)]
|
||
mod tests {
|
||
use super::*;
|
||
|
||
fn flat_grid(w: u32, h: u32, val: f32) -> Vec<f32> {
|
||
vec![val; (w * h) as usize]
|
||
}
|
||
|
||
fn slope_grid(w: u32, h: u32) -> Vec<f32> {
|
||
let n = (w * h) as usize;
|
||
(0..n)
|
||
.map(|i| {
|
||
let r = i / w as usize;
|
||
let c = i % w as usize;
|
||
// Slope: higher in top-left, drains toward bottom-right.
|
||
1.0 - (r as f32 / h as f32 * 0.5 + c as f32 / w as f32 * 0.5)
|
||
})
|
||
.collect()
|
||
}
|
||
|
||
#[test]
|
||
fn flat_grid_produces_single_basin() {
|
||
let elev = flat_grid(16, 8, 0.5);
|
||
let result = analyze(&elev, 16, 8, 0.3);
|
||
// Flat world → no pour points → single basin
|
||
assert_eq!(result.drainage_basins.len(), 1);
|
||
assert!((result.drainage_basins[0].area_pct - 1.0).abs() < 0.01);
|
||
}
|
||
|
||
#[test]
|
||
fn slope_grid_has_no_river_cells_below_threshold_by_default() {
|
||
// Small 8×4 grid: max flow_accum ≤ 32, below RIVER_THRESHOLD (200).
|
||
let elev = slope_grid(8, 4);
|
||
let result = analyze(&elev, 8, 4, 0.3);
|
||
// River cells may be empty on this tiny grid — that is acceptable.
|
||
// What matters: no panic and basin count ≥ 1.
|
||
assert!(!result.drainage_basins.is_empty());
|
||
}
|
||
|
||
#[test]
|
||
fn large_grid_river_cells_nonempty() {
|
||
// 512×256: max flow accumulation ~131K >> RIVER_THRESHOLD.
|
||
let elev = slope_grid(512, 256);
|
||
let result = analyze(&elev, 512, 256, 0.3);
|
||
assert!(
|
||
!result.river_network.river_cells.is_empty(),
|
||
"Expected river cells on a large sloped grid"
|
||
);
|
||
}
|
||
|
||
#[test]
|
||
fn basin_area_pcts_sum_to_one() {
|
||
let elev = slope_grid(64, 32);
|
||
let result = analyze(&elev, 64, 32, 0.3);
|
||
let total: f32 = result.drainage_basins.iter().map(|b| b.area_pct).sum();
|
||
assert!(
|
||
(total - 1.0).abs() < 0.01,
|
||
"Basin area fractions must sum to 1, got {}",
|
||
total
|
||
);
|
||
}
|
||
|
||
#[test]
|
||
fn basin_count_within_target_range() {
|
||
let elev = slope_grid(128, 64);
|
||
let result = analyze(&elev, 128, 64, 0.3);
|
||
let n = result.drainage_basins.len();
|
||
assert!(
|
||
(1..=12).contains(&n),
|
||
"Basin count {} out of expected range [1, 12]",
|
||
n
|
||
);
|
||
}
|
||
|
||
#[test]
|
||
fn determinism() {
|
||
// Running analyze twice on the same input must produce identical results.
|
||
let elev = slope_grid(64, 32);
|
||
let r1 = analyze(&elev, 64, 32, 0.3);
|
||
let r2 = analyze(&elev, 64, 32, 0.3);
|
||
assert_eq!(
|
||
r1.river_network.river_cells, r2.river_network.river_cells,
|
||
"River cells must be deterministic"
|
||
);
|
||
assert_eq!(
|
||
r1.drainage_basins.len(),
|
||
r2.drainage_basins.len(),
|
||
"Basin count must be deterministic"
|
||
);
|
||
}
|
||
|
||
#[test]
|
||
fn flow_accumulation_deterministic_and_clamped() {
|
||
// flow_accumulation/max_accumulation are the D-209 strength denominator —
|
||
// a silent drift corrupts every attractor strength. Lock them down.
|
||
let elev = slope_grid(64, 32);
|
||
let r1 = analyze(&elev, 64, 32, 0.3);
|
||
let r2 = analyze(&elev, 64, 32, 0.3);
|
||
assert_eq!(r1.flow_accumulation, r2.flow_accumulation);
|
||
assert_eq!(r1.max_accumulation, r2.max_accumulation);
|
||
assert!(
|
||
r1.max_accumulation >= 1,
|
||
"max_accumulation must be clamped ≥ 1"
|
||
);
|
||
// Flat / all-ocean world: still well-defined (no division by zero).
|
||
let flat = flat_grid(16, 8, 0.5);
|
||
let rf = analyze(&flat, 16, 8, 0.9); // sea_level above all terrain
|
||
assert!(rf.max_accumulation >= 1);
|
||
}
|
||
|
||
#[test]
|
||
fn isolated_basins_no_panic() {
|
||
// Two land patches split by an ocean band (rows 3-4 below sea level):
|
||
// exercises basin labeling/merge on a disconnected world.
|
||
let (w, h) = (32usize, 8usize);
|
||
let mut elev = vec![0.1f32; w * h]; // ocean everywhere
|
||
for r in [0, 1, 2, 5, 6, 7] {
|
||
for c in 0..w {
|
||
// two raised land bands, sloped so they drain internally
|
||
elev[r * w + c] = 0.5 + (c as f32 / w as f32) * 0.3;
|
||
}
|
||
}
|
||
let res = analyze(&elev, w as u32, h as u32, 0.3);
|
||
let n = res.drainage_basins.len();
|
||
assert!((1..=12).contains(&n), "basin count {n} out of range");
|
||
}
|
||
}
|