1import package::render::mesh_bindings::mesh;
2
3@if(MULTIPLE_LIGHTMAPS_IN_ARRAY)
4enable wgpu_binding_array;
5
6@if(MULTIPLE_LIGHTMAPS_IN_ARRAY) {
7@group(2) @binding(4) var lightmaps_textures: binding_array<texture_2d<f32>, 4>;
8@group(2) @binding(5) var lightmaps_samplers: binding_array<sampler, 4>;
9}
10@else {
11@group(2) @binding(4) var lightmaps_texture: texture_2d<f32>;
12@group(2) @binding(5) var lightmaps_sampler: sampler;
13}
14
15/// Samples the lightmap, if any, and returns indirect illumination from it.
16fn lightmap(uv: vec2<f32>, exposure: f32, instance_index: u32) -> vec3<f32> {
17    let packed_uv_rect = mesh[instance_index].lightmap_uv_rect;
18    let uv_rect = vec4<f32>(
19        unpack2x16unorm(packed_uv_rect.x),
20        unpack2x16unorm(packed_uv_rect.y),
21    );
22    let lightmap_uv = mix(uv_rect.xy, uv_rect.zw, uv);
23    let lightmap_slot = mesh[instance_index].material_and_lightmap_bind_group_slot >> 16u;
24
25    // Bicubic 4-tap
26    // https://developer.nvidia.com/gpugems/gpugems2/part-iii-high-quality-rendering/chapter-20-fast-third-order-texture-filtering
27    // https://advances.realtimerendering.com/s2021/jpatry_advances2021/index.html#/111/0/2
28    var color: vec3<f32>;
29@if(LIGHTMAP_BICUBIC_SAMPLING) {
30    let texture_size = vec2<f32>(lightmap_size(lightmap_slot));
31    let texel_size = 1.0 / texture_size;
32    let puv = lightmap_uv * texture_size + 0.5;
33    let iuv = floor(puv);
34    let fuv = fract(puv);
35    let g0x = g0(fuv.x);
36    let g1x = g1(fuv.x);
37    let h0x = h0_approx(fuv.x);
38    let h1x = h1_approx(fuv.x);
39    let h0y = h0_approx(fuv.y);
40    let h1y = h1_approx(fuv.y);
41    let p0 = (vec2(iuv.x + h0x, iuv.y + h0y) - 0.5) * texel_size;
42    let p1 = (vec2(iuv.x + h1x, iuv.y + h0y) - 0.5) * texel_size;
43    let p2 = (vec2(iuv.x + h0x, iuv.y + h1y) - 0.5) * texel_size;
44    let p3 = (vec2(iuv.x + h1x, iuv.y + h1y) - 0.5) * texel_size;
45    color = g0(fuv.y) * (g0x * sample(p0, lightmap_slot) + g1x * sample(p1, lightmap_slot)) + g1(fuv.y) * (g0x * sample(p2, lightmap_slot) + g1x * sample(p3, lightmap_slot));
46} @else {
47    color = sample(lightmap_uv, lightmap_slot);
48}
49
50    return color * exposure;
51}
52
53fn lightmap_size(lightmap_slot: u32) -> vec2<u32> {
54    @if(MULTIPLE_LIGHTMAPS_IN_ARRAY)
55    return textureDimensions(lightmaps_textures[lightmap_slot]);
56    @else
57    return textureDimensions(lightmaps_texture);
58}
59
60fn sample(uv: vec2<f32>, lightmap_slot: u32) -> vec3<f32> {
61    // Mipmapping lightmaps is usually a bad idea due to leaking across UV
62    // islands, so there's no harm in using mip level 0 and it lets us avoid
63    // control flow uniformity problems.
64    @if(MULTIPLE_LIGHTMAPS_IN_ARRAY)
65    return textureSampleLevel(lightmaps_textures[lightmap_slot], lightmaps_samplers[lightmap_slot], uv, 0.0).rgb;
66    @else
67    return textureSampleLevel(lightmaps_texture, lightmaps_sampler, uv, 0.0).rgb;
68}
69
70fn w0(a: f32) -> f32 {
71    return (1.0 / 6.0) * (a * (a * (-a + 3.0) - 3.0) + 1.0);
72}
73
74fn w1(a: f32) -> f32 {
75    return (1.0 / 6.0) * (a * a * (3.0 * a - 6.0) + 4.0);
76}
77
78fn w2(a: f32) -> f32 {
79    return (1.0 / 6.0) * (a * (a * (-3.0 * a + 3.0) + 3.0) + 1.0);
80}
81
82fn w3(a: f32) -> f32 {
83    return (1.0 / 6.0) * (a * a * a);
84}
85
86fn g0(a: f32) -> f32 {
87    return w0(a) + w1(a);
88}
89
90fn g1(a: f32) -> f32 {
91    return w2(a) + w3(a);
92}
93
94fn h0_approx(a: f32) -> f32 {
95    return -0.2 - a * (0.24 * a - 0.44);
96}
97
98fn h1_approx(a: f32) -> f32 {
99    return 1.0 + a * (0.24 * a - 0.04);
100}