1// Bed-depth and river-body contributions to the composed cascade material.
2
3#define_import_path aqua::shore::water
4
5#import aqua::cascade::{bed_height, cascade_layout, caustics_sampler, caustics_texture, surface}
6
7// Decoded "no bed data" depth: matches a cleared full-depth capture texel.
8
9const NO_BED_DEPTH: f32 = 256.0;
10// Must match the 16-cell startup texture generated by bevy-aqua-shore.
11const CAUSTIC_CELLS_PER_TILE: f32 = 16.0;
12// Restores bright focused ridges after multiplying two sparse samples.
13const CAUSTIC_FOCUS_GAIN: f32 = 12.0;
14// Suppress moonlight-scale directional sources while smoothly admitting daylight.
15const CAUSTIC_DAYLIGHT_MIN_LUX: f32 = 64.0;
16const CAUSTIC_REFERENCE_SUN_LUX: f32 = 120000.0;
17const CAUSTIC_LUMINANCE_WEIGHTS: vec3<f32> = vec3(0.2126, 0.7152, 0.0722);
18
19// River-wave synthesis lives in bevy_aqua_core::river (shared with the
20// wave-query pass).
21
22
23/// Water depth under the sea level from the game's bed height map. Outside
24/// the mapped area (or with no map at all) the sample keeps the deep default,
25/// mirroring a full-depth capture texel.
26fn bed_water_depth(world_xz: vec2<f32>) -> f32 {
27    let range = cascade_layout.bed_range;
28    if range.y < 0.0 {
29        return NO_BED_DEPTH;
30    }
31    let uv = (world_xz - cascade_layout.bed_transform.xy)
32        * cascade_layout.bed_transform.zw;
33    if any(uv < vec2(0.0)) || any(uv > vec2(1.0)) {
34        return NO_BED_DEPTH;
35    }
36    let dimensions = vec2<f32>(textureDimensions(bed_height));
37    let texel_position = uv * (dimensions - vec2(1.0));
38    let base = vec2<i32>(floor(texel_position));
39    let fraction = fract(texel_position);
40    let maximum = i32(dimensions.x) - 1;
41    let maximum_y = i32(dimensions.y) - 1;
42    let p00 = clamp(base, vec2(0), vec2(maximum, maximum_y));
43    let p10 = clamp(base + vec2(1, 0), vec2(0), vec2(maximum, maximum_y));
44    let p01 = clamp(base + vec2(0, 1), vec2(0), vec2(maximum, maximum_y));
45    let p11 = clamp(base + vec2(1), vec2(0), vec2(maximum, maximum_y));
46    let row_0 = mix(
47        textureLoad(bed_height, p00, 0).r,
48        textureLoad(bed_height, p10, 0).r,
49        fraction.x,
50    );
51    let row_1 = mix(
52        textureLoad(bed_height, p01, 0).r,
53        textureLoad(bed_height, p11, 0).r,
54        fraction.x,
55    );
56    let height = mix(row_0, row_1, fraction.y) * range.y + range.x;
57    return max(range.z - height, 0.0);
58}
59
60// The bed map is world-static, so Crest's cascade blending for SeaFloorDepth
61// collapses to one lookup; only the shallow-attenuation cap remains.
62fn blended_water_depth(world_xz: vec2<f32>) -> f32 {
63    return min(bed_water_depth(world_xz), surface.sea_floor.x);
64}
65
66// Direct sunlight reaches the bed before Beer-Lambert mixing.
67fn caustic_bed_radiance(
68    scene_colour: vec3<f32>,
69    world_xz: vec2<f32>,
70    water_depth: f32,
71    time: f32,
72    sun_direction: vec3<f32>,
73    sun_unexposed_radiance: vec3<f32>,
74    sun_shadow: f32,
75    extinction: vec3<f32>,
76) -> vec3<f32> {
77    let strength = surface.caustics.x * surface.sea_floor.w;
78    if strength <= 0.0 {
79        return scene_colour;
80    }
81    let maximum_depth = surface.caustics.w;
82    if water_depth >= maximum_depth || sun_direction.y <= 0.0 || sun_shadow <= 0.0 {
83        return scene_colour;
84    }
85    let scale = surface.caustics.y * CAUSTIC_CELLS_PER_TILE;
86    let scroll = surface.caustics.z * time / scale;
87    // Incommensurate scale and directions prevent the two layers from locking.
88    let uv_a = world_xz / scale + vec2(scroll, 0.63 * scroll);
89    let uv_b = world_xz * 1.37 / scale + vec2(-0.71 * scroll, 0.43 * scroll);
90    let a = textureSampleLevel(caustics_texture, caustics_sampler, uv_a, 0.0).r;
91    let b = textureSampleLevel(caustics_texture, caustics_sampler, uv_b, 0.0).r;
92    let pattern = CAUSTIC_FOCUS_GAIN * a * b;
93    let depth_gate = 1.0 - smoothstep(0.0, maximum_depth, water_depth);
94    let direct_lux = dot(
95        max(sun_unexposed_radiance, vec3(0.0)),
96        CAUSTIC_LUMINANCE_WEIGHTS,
97    );
98    let daylight = clamp(
99        (direct_lux - CAUSTIC_DAYLIGHT_MIN_LUX)
100            / (CAUSTIC_REFERENCE_SUN_LUX - CAUSTIC_DAYLIGHT_MIN_LUX),
101        0.0,
102        1.0,
103    );
104    // The incoming sunlight path lengthens toward the horizon. Outgoing bed
105    // radiance receives the normal camera-path attenuation after this function.
106    let bed_incidence = max(sun_direction.y, 0.0);
107    let incoming_path = water_depth / max(bed_incidence, 0.02);
108    let incoming_transmission = exp(-extinction * incoming_path);
109    let sun_chroma = max(sun_unexposed_radiance, vec3(0.0))
110        / max(direct_lux, CAUSTIC_DAYLIGHT_MIN_LUX);
111    // Focus the bed's existing pre-exposed radiance rather than adding raw lux
112    // as an emissive overlay. This preserves bed color and camera exposure.
113    let focus = strength * depth_gate * pattern * daylight
114        * bed_incidence * sun_shadow;
115    return scene_colour + scene_colour * sun_chroma
116        * incoming_transmission * focus;
117}