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Add loop annotations to ubershaders to prevent loop unrolling. #102480

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Feb 7, 2025
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Add loop annotations to ubershaders to prevent loop unrolling. #102480

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26 changes: 26 additions & 0 deletions servers/rendering/renderer_rd/shaders/scene_forward_lights_inc.glsl
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Original file line number Diff line number Diff line change
@@ -1,5 +1,18 @@
// Functions related to lighting

#extension GL_EXT_control_flow_attributes : require

// This annotation macro must be placed before any loops that rely on specialization constants as their upper bound.
// Drivers may choose to unroll these loops based on the possible range of the value that can be deduced from the
// spec constant, which can lead to their code generation taking a much longer time than desired.
#ifdef UBERSHADER
// Prefer to not unroll loops on the ubershader to reduce code size as much as possible.
#define SPEC_CONSTANT_LOOP_ANNOTATION [[dont_unroll]]
#else
// Don't make an explicit hint on specialized shaders.
#define SPEC_CONSTANT_LOOP_ANNOTATION
#endif

float D_GGX(float cos_theta_m, float alpha) {
float a = cos_theta_m * alpha;
float k = alpha / (1.0 - cos_theta_m * cos_theta_m + a * a);
Expand Down Expand Up @@ -257,6 +270,7 @@ float sample_directional_pcf_shadow(texture2D shadow, vec2 shadow_pixel_size, ve

float avg = 0.0;

SPEC_CONSTANT_LOOP_ANNOTATION
for (uint i = 0; i < sc_directional_soft_shadow_samples(); i++) {
avg += textureProj(sampler2DShadow(shadow, shadow_sampler), vec4(pos + shadow_pixel_size * (disk_rotation * scene_data_block.data.directional_soft_shadow_kernel[i].xy), depth, 1.0));
}
Expand All @@ -283,6 +297,7 @@ float sample_pcf_shadow(texture2D shadow, vec2 shadow_pixel_size, vec3 coord, fl

float avg = 0.0;

SPEC_CONSTANT_LOOP_ANNOTATION
for (uint i = 0; i < sc_soft_shadow_samples(); i++) {
avg += textureProj(sampler2DShadow(shadow, shadow_sampler), vec4(pos + shadow_pixel_size * (disk_rotation * scene_data_block.data.soft_shadow_kernel[i].xy), depth, 1.0));
}
Expand All @@ -309,6 +324,7 @@ float sample_omni_pcf_shadow(texture2D shadow, float blur_scale, vec2 coord, vec
float avg = 0.0;
vec2 offset_scale = blur_scale * 2.0 * scene_data_block.data.shadow_atlas_pixel_size / uv_rect.zw;

SPEC_CONSTANT_LOOP_ANNOTATION
for (uint i = 0; i < sc_soft_shadow_samples(); i++) {
vec2 offset = offset_scale * (disk_rotation * scene_data_block.data.soft_shadow_kernel[i].xy);
vec2 sample_coord = coord + offset;
Expand Down Expand Up @@ -346,6 +362,7 @@ float sample_directional_soft_shadow(texture2D shadow, vec3 pssm_coord, vec2 tex
disk_rotation = mat2(vec2(cr, -sr), vec2(sr, cr));
}

SPEC_CONSTANT_LOOP_ANNOTATION
for (uint i = 0; i < sc_directional_penumbra_shadow_samples(); i++) {
vec2 suv = pssm_coord.xy + (disk_rotation * scene_data_block.data.directional_penumbra_shadow_kernel[i].xy) * tex_scale;
float d = textureLod(sampler2D(shadow, SAMPLER_LINEAR_CLAMP), suv, 0.0).r;
Expand All @@ -362,6 +379,8 @@ float sample_directional_soft_shadow(texture2D shadow, vec3 pssm_coord, vec2 tex
tex_scale *= penumbra;

float s = 0.0;

SPEC_CONSTANT_LOOP_ANNOTATION
for (uint i = 0; i < sc_directional_penumbra_shadow_samples(); i++) {
vec2 suv = pssm_coord.xy + (disk_rotation * scene_data_block.data.directional_penumbra_shadow_kernel[i].xy) * tex_scale;
s += textureProj(sampler2DShadow(shadow, shadow_sampler), vec4(suv, pssm_coord.z, 1.0));
Expand Down Expand Up @@ -465,6 +484,7 @@ void light_process_omni(uint idx, vec3 vertex, vec3 eye_vec, vec3 normal, vec3 v
tangent *= omni_lights.data[idx].soft_shadow_size * omni_lights.data[idx].soft_shadow_scale;
bitangent *= omni_lights.data[idx].soft_shadow_size * omni_lights.data[idx].soft_shadow_scale;

SPEC_CONSTANT_LOOP_ANNOTATION
for (uint i = 0; i < sc_penumbra_shadow_samples(); i++) {
vec2 disk = disk_rotation * scene_data_block.data.penumbra_shadow_kernel[i].xy;

Expand Down Expand Up @@ -501,6 +521,8 @@ void light_process_omni(uint idx, vec3 vertex, vec3 eye_vec, vec3 normal, vec3 v
z_norm += omni_lights.data[idx].inv_radius * omni_lights.data[idx].shadow_bias;

shadow = 0.0;

SPEC_CONSTANT_LOOP_ANNOTATION
for (uint i = 0; i < sc_penumbra_shadow_samples(); i++) {
vec2 disk = disk_rotation * scene_data_block.data.penumbra_shadow_kernel[i].xy;
vec3 pos = local_vert + tangent * disk.x + bitangent * disk.y;
Expand Down Expand Up @@ -757,6 +779,8 @@ void light_process_spot(uint idx, vec3 vertex, vec3 eye_vec, vec3 normal, vec3 v

float uv_size = spot_lights.data[idx].soft_shadow_size * z_norm * spot_lights.data[idx].soft_shadow_scale;
vec2 clamp_max = spot_lights.data[idx].atlas_rect.xy + spot_lights.data[idx].atlas_rect.zw;

SPEC_CONSTANT_LOOP_ANNOTATION
for (uint i = 0; i < sc_penumbra_shadow_samples(); i++) {
vec2 suv = shadow_uv + (disk_rotation * scene_data_block.data.penumbra_shadow_kernel[i].xy) * uv_size;
suv = clamp(suv, spot_lights.data[idx].atlas_rect.xy, clamp_max);
Expand All @@ -774,6 +798,8 @@ void light_process_spot(uint idx, vec3 vertex, vec3 eye_vec, vec3 normal, vec3 v
uv_size *= penumbra;

shadow = 0.0;

SPEC_CONSTANT_LOOP_ANNOTATION
for (uint i = 0; i < sc_penumbra_shadow_samples(); i++) {
vec2 suv = shadow_uv + (disk_rotation * scene_data_block.data.penumbra_shadow_kernel[i].xy) * uv_size;
suv = clamp(suv, spot_lights.data[idx].atlas_rect.xy, clamp_max);
Expand Down