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::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    // the construction of the up and right vectors needs to precisely mirror the code
92    // in render/light.rs:spot_light_view_matrix
93    var sign = -1.0;
94    if (fwd.z >= 0.0) {
95        sign = 1.0;
96    }
97    let a = -1.0 / (fwd.z + sign);
98    let b = fwd.x * fwd.y * a;
99    let up_dir = vec3<f32>(1.0 + sign * fwd.x * fwd.x * a, sign * b, -sign * fwd.x);
100    let right_dir = vec3<f32>(-b, -sign - fwd.y * fwd.y * a, fwd.y);
101    let light_inv_rot = mat3x3<f32>(right_dir, up_dir, fwd);
102
103    // because the matrix is a pure rotation matrix, the inverse is just the transpose, and to calculate
104    // the product of the transpose with a vector we can just post-multiply instead of pre-multiplying.
105    // this allows us to keep the matrix construction code identical between CPU and GPU.
106    let projected_position = offset_position * light_inv_rot;
107
108    // divide xy by perspective matrix "f" and by -projected.z (projected.z is -projection matrix's w)
109    // to get ndc coordinates
110    let f_div_minus_z = 1.0 / ((*light).spot_light_tan_angle * -projected_position.z);
111    let shadow_xy_ndc = projected_position.xy * f_div_minus_z;
112    // convert to uv coordinates
113    let shadow_uv = shadow_xy_ndc * vec2<f32>(0.5, -0.5) + vec2<f32>(0.5, 0.5);
114
115    let depth = near_z / -projected_position.z;
116
117    // If soft shadows are enabled, use the PCSS path.
118    let array_index = i32(light_id) + view_bindings::lights.spot_light_shadowmap_offset;
119    if ((*light).soft_shadow_size > 0.0) {
120        return sample_shadow_map_pcss(
121            shadow_uv, depth, array_index, SPOT_SHADOW_TEXEL_SIZE, (*light).soft_shadow_size);
122    }
123
124    return sample_shadow_map(shadow_uv, depth, array_index, SPOT_SHADOW_TEXEL_SIZE);
125}
126
127fn get_cascade_index(light_id: u32, view_z: f32) -> u32 {
128    let light = &view_bindings::lights.directional_lights[light_id];
129
130    for (var i: u32 = 0u; i < (*light).num_cascades; i = i + 1u) {
131        if (-view_z < (*light).cascades[i].far_bound) {
132            return i;
133        }
134    }
135    return (*light).num_cascades;
136}
137
138// Converts from world space to the uv position in the light's shadow map.
139//
140// The depth is stored in the return value's z coordinate. If the return value's
141// w coordinate is 0.0, then we landed outside the shadow map entirely.
142fn world_to_directional_light_local(
143    light_id: u32,
144    cascade_index: u32,
145    offset_position: vec4<f32>
146) -> vec4<f32> {
147    let light = &view_bindings::lights.directional_lights[light_id];
148    let cascade = &(*light).cascades[cascade_index];
149
150    let offset_position_clip = (*cascade).clip_from_world * offset_position;
151    if (offset_position_clip.w <= 0.0) {
152        return vec4(0.0);
153    }
154    let offset_position_ndc = offset_position_clip.xyz / offset_position_clip.w;
155    // No shadow outside the orthographic projection volume
156    if (any(offset_position_ndc.xy < vec2<f32>(-1.0)) || offset_position_ndc.z < 0.0
157            || any(offset_position_ndc > vec3<f32>(1.0))) {
158        return vec4(0.0);
159    }
160
161    // compute texture coordinates for shadow lookup, compensating for the Y-flip difference
162    // between the NDC and texture coordinates
163    let flip_correction = vec2<f32>(0.5, -0.5);
164    let light_local = offset_position_ndc.xy * flip_correction + vec2<f32>(0.5, 0.5);
165
166    let depth = offset_position_ndc.z;
167
168    return vec4(light_local, depth, 1.0);
169}
170
171fn sample_directional_cascade(
172    light_id: u32,
173    cascade_index: u32,
174    frag_position: vec4<f32>,
175    surface_normal: vec3<f32>,
176) -> f32 {
177    let light = &view_bindings::lights.directional_lights[light_id];
178    let cascade = &(*light).cascades[cascade_index];
179
180    // The normal bias is scaled to the texel size.
181    let normal_offset = (*light).shadow_normal_bias * (*cascade).texel_size * surface_normal.xyz;
182    let depth_offset = (*light).shadow_depth_bias * (*light).direction_to_light.xyz;
183    let offset_position = vec4<f32>(frag_position.xyz + normal_offset + depth_offset, frag_position.w);
184
185    let light_local = world_to_directional_light_local(light_id, cascade_index, offset_position);
186    if (light_local.w == 0.0) {
187        return 1.0;
188    }
189
190    let array_index = i32((*light).depth_texture_base_index + cascade_index);
191    let texel_size = (*cascade).texel_size;
192
193    // If soft shadows are enabled, use the PCSS path.
194    if ((*light).soft_shadow_size > 0.0) {
195        return sample_shadow_map_pcss(
196            light_local.xy, light_local.z, array_index, texel_size, (*light).soft_shadow_size);
197    }
198
199    return sample_shadow_map(light_local.xy, light_local.z, array_index, texel_size);
200}
201
202fn fetch_directional_shadow(light_id: u32, frag_position: vec4<f32>, surface_normal: vec3<f32>, view_z: f32) -> f32 {
203    let light = &view_bindings::lights.directional_lights[light_id];
204    let cascade_index = get_cascade_index(light_id, view_z);
205
206    if (cascade_index >= (*light).num_cascades) {
207        return 1.0;
208    }
209
210    var shadow = sample_directional_cascade(light_id, cascade_index, frag_position, surface_normal);
211
212    // Blend with the next cascade, if there is one.
213    let next_cascade_index = cascade_index + 1u;
214    if (next_cascade_index < (*light).num_cascades) {
215        let this_far_bound = (*light).cascades[cascade_index].far_bound;
216        let next_near_bound = (1.0 - (*light).cascades_overlap_proportion) * this_far_bound;
217        if (-view_z >= next_near_bound) {
218            let next_shadow = sample_directional_cascade(light_id, next_cascade_index, frag_position, surface_normal);
219            shadow = mix(shadow, next_shadow, (-view_z - next_near_bound) / (this_far_bound - next_near_bound));
220        }
221    }
222    return shadow;
223}
224
225fn cascade_debug_visualization(
226    output_color: vec3<f32>,
227    light_id: u32,
228    view_z: f32,
229) -> vec3<f32> {
230    let overlay_alpha = 0.95;
231    let cascade_index = get_cascade_index(light_id, view_z);
232    let cascade_color_hsv = vec3(
233        f32(cascade_index) / f32(#{MAX_CASCADES_PER_LIGHT}u + 1u) * PI_2,
234        1.0,
235        0.5
236    );
237    let cascade_color = hsv_to_rgb(cascade_color_hsv);
238    return vec3<f32>(
239        (1.0 - overlay_alpha) * output_color.rgb + overlay_alpha * cascade_color
240    );
241}