1#define_import_path bevy_pbr::shadows
2
3#import bevy_pbr::{
4    mesh_view_types::POINT_LIGHT_FLAGS_SPOT_LIGHT_Y_NEGATIVE,
5    mesh_view_bindings as view_bindings,
6    shadow_sampling::{
7        SPOT_SHADOW_TEXEL_SIZE, sample_shadow_cubemap, sample_shadow_cubemap_pcss,
8        sample_shadow_map, sample_shadow_map_pcss,
9    }
10}
11
12#import bevy_render::{
13    color_operations::hsv_to_rgb,
14    maths::{orthonormalize, PI_2}
15}
16
17const flip_z: vec3<f32> = vec3<f32>(1.0, 1.0, -1.0);
18
19fn fetch_point_shadow(light_id: u32, frag_position: vec4<f32>, surface_normal: vec3<f32>) -> f32 {
20    let light = &view_bindings::clusterable_objects.data[light_id];
21
22    // because the shadow maps align with the axes and the frustum planes are at 45 degrees
23    // we can get the worldspace depth by taking the largest absolute axis
24    let surface_to_light = (*light).position_radius.xyz - frag_position.xyz;
25    let surface_to_light_abs = abs(surface_to_light);
26    let distance_to_light = max(surface_to_light_abs.x, max(surface_to_light_abs.y, surface_to_light_abs.z));
27
28    // The normal bias here is already scaled by the texel size at 1 world unit from the light.
29    // The texel size increases proportionally with distance from the light so multiplying by
30    // distance to light scales the normal bias to the texel size at the fragment distance.
31    let normal_offset = (*light).shadow_normal_bias * distance_to_light * surface_normal.xyz;
32    let depth_offset = (*light).shadow_depth_bias * normalize(surface_to_light.xyz);
33    let offset_position = frag_position.xyz + normal_offset + depth_offset;
34
35    // similar largest-absolute-axis trick as above, but now with the offset fragment position
36    let frag_ls = offset_position.xyz - (*light).position_radius.xyz ;
37    let abs_position_ls = abs(frag_ls);
38    let major_axis_magnitude = max(abs_position_ls.x, max(abs_position_ls.y, abs_position_ls.z));
39
40    // NOTE: These simplifications come from multiplying:
41    // projection * vec4(0, 0, -major_axis_magnitude, 1.0)
42    // and keeping only the terms that have any impact on the depth.
43    // Projection-agnostic approach:
44    let zw = -major_axis_magnitude * (*light).light_custom_data.xy + (*light).light_custom_data.zw;
45    let depth = zw.x / zw.y;
46
47    // If soft shadows are enabled, use the PCSS path. Cubemaps assume a
48    // left-handed coordinate space, so we have to flip the z-axis when
49    // sampling.
50    if ((*light).soft_shadow_size > 0.0) {
51        return sample_shadow_cubemap_pcss(
52            frag_ls * flip_z,
53            distance_to_light,
54            depth,
55            light_id,
56            (*light).soft_shadow_size,
57        );
58    }
59
60    // Do the lookup, using HW PCF and comparison. Cubemaps assume a left-handed
61    // coordinate space, so we have to flip the z-axis when sampling.
62    return sample_shadow_cubemap(frag_ls * flip_z, distance_to_light, depth, light_id);
63}
64
65fn fetch_spot_shadow(
66    light_id: u32,
67    frag_position: vec4<f32>,
68    surface_normal: vec3<f32>,
69    near_z: f32,
70) -> f32 {
71    let light = &view_bindings::clusterable_objects.data[light_id];
72
73    let surface_to_light = (*light).position_radius.xyz - frag_position.xyz;
74
75    // construct the light view matrix
76    var spot_dir = vec3<f32>((*light).light_custom_data.x, 0.0, (*light).light_custom_data.y);
77    // reconstruct spot dir from x/z and y-direction flag
78    spot_dir.y = sqrt(max(0.0, 1.0 - spot_dir.x * spot_dir.x - spot_dir.z * spot_dir.z));
79    if (((*light).flags & POINT_LIGHT_FLAGS_SPOT_LIGHT_Y_NEGATIVE) != 0u) {
80        spot_dir.y = -spot_dir.y;
81    }
82
83    // view matrix z_axis is the reverse of transform.forward()
84    let fwd = -spot_dir;
85    let distance_to_light = dot(fwd, surface_to_light);
86    let offset_position =
87        -surface_to_light
88        + ((*light).shadow_depth_bias * normalize(surface_to_light))
89        + (surface_normal.xyz * (*light).shadow_normal_bias) * distance_to_light;
90
91    let light_inv_rot = orthonormalize(fwd);
92
93    // because the matrix is a pure rotation matrix, the inverse is just the transpose, and to calculate
94    // the product of the transpose with a vector we can just post-multiply instead of pre-multiplying.
95    // this allows us to keep the matrix construction code identical between CPU and GPU.
96    let projected_position = offset_position * light_inv_rot;
97
98    // divide xy by perspective matrix "f" and by -projected.z (projected.z is -projection matrix's w)
99    // to get ndc coordinates
100    let f_div_minus_z = 1.0 / ((*light).spot_light_tan_angle * -projected_position.z);
101    let shadow_xy_ndc = projected_position.xy * f_div_minus_z;
102    // convert to uv coordinates
103    let shadow_uv = shadow_xy_ndc * vec2<f32>(0.5, -0.5) + vec2<f32>(0.5, 0.5);
104
105    let depth = near_z / -projected_position.z;
106
107    // If soft shadows are enabled, use the PCSS path.
108    let array_index = i32(light_id) + view_bindings::lights.spot_light_shadowmap_offset;
109    if ((*light).soft_shadow_size > 0.0) {
110        return sample_shadow_map_pcss(
111            shadow_uv, depth, array_index, SPOT_SHADOW_TEXEL_SIZE, (*light).soft_shadow_size);
112    }
113
114    return sample_shadow_map(shadow_uv, depth, array_index, SPOT_SHADOW_TEXEL_SIZE);
115}
116
117fn get_cascade_index(light_id: u32, view_z: f32) -> u32 {
118    let light = &view_bindings::lights.directional_lights[light_id];
119
120    for (var i: u32 = 0u; i < (*light).num_cascades; i = i + 1u) {
121        if (-view_z < (*light).cascades[i].far_bound) {
122            return i;
123        }
124    }
125    return (*light).num_cascades;
126}
127
128// Converts from world space to the uv position in the light's shadow map.
129//
130// The depth is stored in the return value's z coordinate. If the return value's
131// w coordinate is 0.0, then we landed outside the shadow map entirely.
132fn world_to_directional_light_local(
133    light_id: u32,
134    cascade_index: u32,
135    offset_position: vec4<f32>
136) -> vec4<f32> {
137    let light = &view_bindings::lights.directional_lights[light_id];
138    let cascade = &(*light).cascades[cascade_index];
139
140    let offset_position_clip = (*cascade).clip_from_world * offset_position;
141    if (offset_position_clip.w <= 0.0) {
142        return vec4(0.0);
143    }
144    let offset_position_ndc = offset_position_clip.xyz / offset_position_clip.w;
145    // No shadow outside the orthographic projection volume
146    if (any(offset_position_ndc.xy < vec2<f32>(-1.0)) || offset_position_ndc.z < 0.0
147            || any(offset_position_ndc > vec3<f32>(1.0))) {
148        return vec4(0.0);
149    }
150
151    // compute texture coordinates for shadow lookup, compensating for the Y-flip difference
152    // between the NDC and texture coordinates
153    let flip_correction = vec2<f32>(0.5, -0.5);
154    let light_local = offset_position_ndc.xy * flip_correction + vec2<f32>(0.5, 0.5);
155
156    let depth = offset_position_ndc.z;
157
158    return vec4(light_local, depth, 1.0);
159}
160
161fn sample_directional_cascade(
162    light_id: u32,
163    cascade_index: u32,
164    frag_position: vec4<f32>,
165    surface_normal: vec3<f32>,
166) -> f32 {
167    let light = &view_bindings::lights.directional_lights[light_id];
168    let cascade = &(*light).cascades[cascade_index];
169
170    // The normal bias is scaled to the texel size.
171    let normal_offset = (*light).shadow_normal_bias * (*cascade).texel_size * surface_normal.xyz;
172    let depth_offset = (*light).shadow_depth_bias * (*light).direction_to_light.xyz;
173    let offset_position = vec4<f32>(frag_position.xyz + normal_offset + depth_offset, frag_position.w);
174
175    let light_local = world_to_directional_light_local(light_id, cascade_index, offset_position);
176    if (light_local.w == 0.0) {
177        return 1.0;
178    }
179
180    let array_index = i32((*light).depth_texture_base_index + cascade_index);
181    let texel_size = (*cascade).texel_size;
182
183    // If soft shadows are enabled, use the PCSS path.
184    if ((*light).soft_shadow_size > 0.0) {
185        return sample_shadow_map_pcss(
186            light_local.xy, light_local.z, array_index, texel_size, (*light).soft_shadow_size);
187    }
188
189    return sample_shadow_map(light_local.xy, light_local.z, array_index, texel_size);
190}
191
192fn fetch_directional_shadow(light_id: u32, frag_position: vec4<f32>, surface_normal: vec3<f32>, view_z: f32) -> f32 {
193    let light = &view_bindings::lights.directional_lights[light_id];
194    let cascade_index = get_cascade_index(light_id, view_z);
195
196    if (cascade_index >= (*light).num_cascades) {
197        return 1.0;
198    }
199
200    var shadow = sample_directional_cascade(light_id, cascade_index, frag_position, surface_normal);
201
202    // Blend with the next cascade, if there is one.
203    let next_cascade_index = cascade_index + 1u;
204    if (next_cascade_index < (*light).num_cascades) {
205        let this_far_bound = (*light).cascades[cascade_index].far_bound;
206        let next_near_bound = (1.0 - (*light).cascades_overlap_proportion) * this_far_bound;
207        if (-view_z >= next_near_bound) {
208            let next_shadow = sample_directional_cascade(light_id, next_cascade_index, frag_position, surface_normal);
209            shadow = mix(shadow, next_shadow, (-view_z - next_near_bound) / (this_far_bound - next_near_bound));
210        }
211    }
212    return shadow;
213}
214
215fn cascade_debug_visualization(
216    output_color: vec3<f32>,
217    light_id: u32,
218    view_z: f32,
219) -> vec3<f32> {
220    let overlay_alpha = 0.95;
221    let cascade_index = get_cascade_index(light_id, view_z);
222    let cascade_color_hsv = vec3(
223        f32(cascade_index) / f32(#{MAX_CASCADES_PER_LIGHT}u + 1u) * PI_2,
224        1.0,
225        0.5
226    );
227    let cascade_color = hsv_to_rgb(cascade_color_hsv);
228    return vec3<f32>(
229        (1.0 - overlay_alpha) * output_color.rgb + overlay_alpha * cascade_color
230    );
231}