shader_type spatial;
render_mode diffuse_lambert, specular_disabled;

// T-1088 greybox wall + camera-side cutaway (design §8) — technique
// proto-production.
//
// COLOR-multiplied albedo (same four-state tint contract as the floor shader)
// plus a smoothstep height cut along the CAMERA->CHARACTER SIGHTLINE CORRIDOR:
// walls inside the corridor drop to a CUT_HEIGHT stub — the Xenonauts read,
// aligned to what actually occludes the character (the earlier proximity dome
// bit side walls while leaving the occluding wall standing). The cutaway cuts
// RENDER HEIGHT; the tint gates KNOWLEDGE — independent factors, so remembered
// walls can be cut too. Open box tops are acceptable greybox fidelity; ghost
// band / dither / capping are named polish on this same shader.
//
// Corridor geometry (world space — the camera has yaw 0 and looks world -Z;
// the diamond view is WorldRoot's 45 deg rotation, never the camera's, D-148):
// the ground projection of the camera->character sightline is the +Z half-line
// at the character's x. A wall occludes the character only within
// |to_wall.x| < corridor half-width AND 0 < to_wall.y < reach, where reach is
// pitch-derived (a WALL_H wall can occlude someone at most WALL_H / tan(pitch)
// away in ortho): ~4.3 m at the -30 deg gameplay preset, long at -5 frontal,
// near-zero at -80 overhead. u_char_pos_xz + u_cut_reach are pushed per frame
// (GreyboxWorld.set_cutaway_char_pos) so the corridor glides with the character
// and breathes with the tilt. Parked far away by default: no cut until pushed.
//
// Static uniforms default to the SandboxConstants values; GreyboxWorld pushes
// them at material build so SandboxConstants stays the single source (§12).

uniform vec2 u_char_pos_xz = vec2(1000000.0, 1000000.0);
uniform float u_wall_h = 2.5;            // SandboxConstants.WALL_H
uniform float u_cut_height = 0.75;       // SandboxConstants.CUT_HEIGHT — the stub
uniform float u_corridor_half_w = 1.4;   // SandboxConstants.CUT_CORRIDOR_HALF_W
uniform float u_cut_band = 0.75;         // SandboxConstants.CUT_BAND — falloff band
uniform float u_cut_reach = 4.4;         // per-frame: WALL_H / tan(camera pitch)
// 0 = sightline corridor, 1 = bottom walls low, 2 = both (live-toggled, C key).
uniform int u_cutaway_mode = 0;
uniform vec3 u_base_albedo : source_color = vec3(0.66, 0.64, 0.60);

varying vec3 v_world_pos;
// Whole-box cut decision, computed per-INSTANCE in vertex() from the box's tile
// center — every wall box is either full height or the stub, no per-fragment
// falloff curves carving organic notches (the "sphere" read). X2-crisp tile
// cuts; the smoothstep bands only shape where the 0.5 threshold falls.
varying flat float v_cut;

void vertex() {
    // MODEL_MATRIX folds in the per-instance MultiMesh transform; its origin
    // is the box center — .xz is the wall tile's center in world space.
    vec2 inst_xz = (MODEL_MATRIX * vec4(0.0, 0.0, 0.0, 1.0)).xz;
    vec2 to_wall = inst_xz - u_char_pos_xz;
    // Lateral gate: full cut inside (half_w - band), fading to none at half_w.
    float lateral = 1.0 - smoothstep(u_corridor_half_w - u_cut_band, u_corridor_half_w, abs(to_wall.x));
    // Near gate: soft start just behind the character (no hard seam at their feet).
    float near_f = smoothstep(-0.25, 0.75, to_wall.y);
    // Far gate: corridor ends where a WALL_H wall can no longer occlude.
    float far_f = 1.0 - smoothstep(u_cut_reach, u_cut_reach + u_cut_band, to_wall.y);
    float corridor_f = lateral * near_f * far_f;
    // Bottom-wall flag (INSTANCE_CUSTOM.r, GreyboxWorld): KNOWN non-wall tile
    // behind this wall run — it would occlude interior the player should see.
    float cut_f = corridor_f;
    if (u_cutaway_mode == 1) {
        cut_f = INSTANCE_CUSTOM.r;
    } else if (u_cutaway_mode == 2) {
        cut_f = max(corridor_f, INSTANCE_CUSTOM.r);
    }
    v_cut = cut_f > 0.5 ? 1.0 : 0.0;
    v_world_pos = (MODEL_MATRIX * vec4(VERTEX, 1.0)).xyz;
}

void fragment() {
    float allowed = mix(u_wall_h, u_cut_height, v_cut);
    if (v_world_pos.y > allowed) {
        discard;
    }
    ALBEDO = u_base_albedo * COLOR.rgb;
    ROUGHNESS = 1.0;
}