shader_type spatial;
render_mode diffuse_lambert, specular_disabled;

// T-1088 greybox floor (design §3.3) — sandbox-only.
//
// Per-instance visibility tint x world-space grid lines. The MultiMesh instance
// color (use_colors, GreyboxWorld) arrives as the COLOR built-in and multiplies
// albedo: white = Forward, 85% = Peripheral, 70% = BoundaryWall, dim cool grey =
// Remembered (SandboxConstants.TINTS — §3.2).
//
// Grid: data is per-0.5 m subtile (D-066/D-222) but the floor must READ as 1 m
// visual tiles (2x2 subtiles) — minor lines every 0.5 m (alpha 0.15), major
// lines every 1.0 m (alpha 0.45). Lines are sampled in SIM space (u_sim_from_world
// undoes the 45 deg WorldRoot rotation) so they land on tile edges; sampling raw
// world space would draw the grid rotated 45 deg against the tiles. Continuous
// across instances because sim space is shared. D-243's "voxel = 1 m" is
// generation-cascade vocabulary — the 1 m visual tile exists ONLY as the major
// lines here (§2).

uniform vec3 u_base_albedo : source_color = vec3(0.52, 0.54, 0.58);
uniform vec3 u_line_albedo : source_color = vec3(0.10, 0.11, 0.14);
uniform float u_minor_spacing_m = 0.5;
uniform float u_major_spacing_m = 1.0;
uniform float u_minor_alpha = 0.15;
uniform float u_major_alpha = 0.45;
uniform float u_line_half_width_m = 0.02;
// World -> sim-space transform; set by GreyboxWorld from its own inverse global
// transform so the grid rotates WITH the tiles under the WorldRoot 45 deg.
uniform mat4 u_sim_from_world = mat4(1.0);

varying vec2 v_world_xz;

void vertex() {
    // MODEL_MATRIX folds in the per-instance MultiMesh transform (incl. WorldRoot
    // rotation); u_sim_from_world undoes the scene rotation back to sim axes.
    v_world_xz = (u_sim_from_world * MODEL_MATRIX * vec4(VERTEX, 1.0)).xz;
}

// 1.0 on a grid line of the given spacing, 0.0 off it, one-fwidth AA edge.
float line_mask(vec2 p, float spacing, float half_width) {
    vec2 dxy = abs(fract(p / spacing + 0.5) - 0.5) * spacing;  // metres to nearest line
    float d = min(dxy.x, dxy.y);
    float aa = fwidth(d);
    return 1.0 - smoothstep(half_width - aa, half_width + aa, d);
}

void fragment() {
    float minor = line_mask(v_world_xz, u_minor_spacing_m, u_line_half_width_m) * u_minor_alpha;
    float major = line_mask(v_world_xz, u_major_spacing_m, u_line_half_width_m) * u_major_alpha;
    float line_a = max(minor, major);  // major wins where the grids coincide
    vec3 tinted = u_base_albedo * COLOR.rgb;
    // Line color is tinted too, so remembered/peripheral tiles keep dim lines.
    ALBEDO = mix(tinted, u_line_albedo * COLOR.rgb, line_a);
    ROUGHNESS = 1.0;
}