EEVEE-Next: Irradiance Grid smooth transitions

Smooth the transition at grid bounds.

The transition size is fixed at 1 grid cell,
but it may be useful to expose a user setting for controlling this.

Pull Request: https://projects.blender.org/blender/blender/pulls/112842

source/blender/draw/engines/eevee_next/eevee_raytrace.cc

@@ -143,6 +143,7 @@ void RayTraceModule::sync()
     inst_.bind_uniform_data(&pass);
     inst_.irradiance_cache.bind_resources(pass);
     inst_.reflection_probes.bind_resources(pass);
+    inst_.sampling.bind_resources(pass);
     pass.dispatch(raytrace_tracing_dispatch_buf_);
     pass.barrier(GPU_BARRIER_SHADER_IMAGE_ACCESS);
   }

source/blender/draw/engines/eevee_next/eevee_reflection_probes.cc

@@ -216,6 +216,7 @@ void ReflectionProbeModule::begin_sync()
     pass.push_constant("reflection_probe_count", &reflection_probe_count_);
     pass.bind_ssbo("reflection_probe_buf", &data_buf_);
     instance_.irradiance_cache.bind_resources(pass);
+    instance_.sampling.bind_resources(pass);
     pass.dispatch(&dispatch_probe_select_);
     pass.barrier(GPU_BARRIER_UNIFORM);
   }

source/blender/draw/engines/eevee_next/eevee_shader_shared.hh

@@ -1476,6 +1476,15 @@ BLI_STATIC_ASSERT_ALIGN(UniformData, 16)
 
 /* __cplusplus is true when compiling with MSL, so include if inside a shader. */
 #if !defined(__cplusplus) || defined(GPU_SHADER)
+
+#  if defined(GPU_FRAGMENT_SHADER)
+#    define UTIL_TEXEL vec2(gl_FragCoord)
+#  elif defined(GPU_COMPUTE_SHADER)
+#    define UTIL_TEXEL vec2(gl_GlobalInvocationID)
+#  else
+#    define UTIL_TEXEL vec2(gl_VertexID, 0)
+#  endif
+
 /* Fetch texel. Wrapping if above range. */
 float4 utility_tx_fetch(sampler2DArray util_tx, float2 texel, float layer)
 {

source/blender/draw/engines/eevee_next/shaders/eevee_lightprobe_eval_lib.glsl

@@ -7,11 +7,15 @@
  * - grids_infos_buf
  * - bricks_infos_buf
  * - irradiance_atlas_tx
+ * Needed for sampling (not for upload):
+ * - util_tx
+ * - sampling_buf
  */
 
 #pragma BLENDER_REQUIRE(gpu_shader_codegen_lib.glsl)
 #pragma BLENDER_REQUIRE(eevee_lightprobe_lib.glsl)
 #pragma BLENDER_REQUIRE(eevee_spherical_harmonics_lib.glsl)
+#pragma BLENDER_REQUIRE(eevee_sampling_lib.glsl)
 #pragma BLENDER_REQUIRE(eevee_reflection_probe_eval_lib.glsl)
 #pragma BLENDER_REQUIRE(gpu_shader_math_base_lib.glsl)
 
@@ -126,19 +130,35 @@ SphericalHarmonicL1 lightprobe_irradiance_sample(
     sampler3D atlas_tx, vec3 P, vec3 V, vec3 Ng, const bool do_bias)
 {
   vec3 lP;
-  int index = 0;
+  int index = -1;
+  int i = 0;
 #ifdef IRRADIANCE_GRID_UPLOAD
-  index = grid_start_index;
+  i = grid_start_index;
 #endif
-  for (; index < IRRADIANCE_GRID_MAX; index++) {
+#ifdef IRRADIANCE_GRID_SAMPLING
+  float random = interlieved_gradient_noise(UTIL_TEXEL, 0.0, 0.0);
+  random = fract(random + sampling_rng_1D_get(SAMPLING_LIGHTPROBE));
+#endif
+  for (; i < IRRADIANCE_GRID_MAX; i++) {
     /* Last grid is tagged as invalid to stop the iteration. */
-    if (grids_infos_buf[index].grid_size.x == -1) {
+    if (grids_infos_buf[i].grid_size.x == -1) {
       /* Sample the last grid instead. */
-      index -= 1;
+      index = i - 1;
       break;
     }
+
     /* If sample fall inside the grid, step out of the loop. */
-    if (lightprobe_irradiance_grid_local_coord(grids_infos_buf[index], P, lP)) {
+    if (lightprobe_irradiance_grid_local_coord(grids_infos_buf[i], P, lP)) {
+      index = i;
+#ifdef IRRADIANCE_GRID_SAMPLING
+      float distance_to_border = reduce_min(min(lP, vec3(grids_infos_buf[i].grid_size) - lP));
+      if (distance_to_border < random) {
+        /* Remap random to the remaining interval. */
+        random = (random - distance_to_border) / (1.0 - distance_to_border);
+        /* Try to sample another grid to get smooth transitions at borders. */
+        continue;
+      }
+#endif
       break;
     }
   }

source/blender/draw/engines/eevee_next/shaders/infos/eevee_irradiance_cache_info.hh

@@ -204,7 +204,8 @@ GPU_SHADER_CREATE_INFO(eevee_volume_probe_data)
     /* NOTE: Use uint instead of IrradianceBrickPacked because Metal needs to know the exact type.
      */
     .storage_buf(IRRADIANCE_BRICK_BUF_SLOT, Qualifier::READ, "uint", "bricks_infos_buf[]")
-    .sampler(IRRADIANCE_ATLAS_TEX_SLOT, ImageType::FLOAT_3D, "irradiance_atlas_tx");
+    .sampler(IRRADIANCE_ATLAS_TEX_SLOT, ImageType::FLOAT_3D, "irradiance_atlas_tx")
+    .define("IRRADIANCE_GRID_SAMPLING");
 
 GPU_SHADER_CREATE_INFO(eevee_lightprobe_data)
     .additional_info("eevee_reflection_probe_data", "eevee_volume_probe_data");

source/blender/draw/engines/eevee_next/shaders/infos/eevee_reflection_probe_info.hh

@@ -46,7 +46,7 @@ GPU_SHADER_CREATE_INFO(eevee_reflection_probe_select)
                  "ReflectionProbeData",
                  "reflection_probe_buf[REFLECTION_PROBES_MAX]")
     .push_constant(Type::INT, "reflection_probe_count")
-    .additional_info("eevee_shared", "eevee_volume_probe_data")
+    .additional_info("eevee_shared", "eevee_sampling_data", "eevee_volume_probe_data")
     .compute_source("eevee_reflection_probe_select_comp.glsl")
     .do_static_compilation(true);
 

source/blender/draw/engines/eevee_next/shaders/infos/eevee_tracing_info.hh

@@ -78,7 +78,11 @@ EEVEE_RAYTRACE_CLOSURE_VARIATION(eevee_ray_generate)
 GPU_SHADER_CREATE_INFO(eevee_ray_trace_fallback)
     .do_static_compilation(true)
     .local_group_size(RAYTRACE_GROUP_SIZE, RAYTRACE_GROUP_SIZE)
-    .additional_info("eevee_shared", "eevee_global_ubo", "draw_view", "eevee_lightprobe_data")
+    .additional_info("eevee_shared",
+                     "eevee_global_ubo",
+                     "draw_view",
+                     "eevee_sampling_data",
+                     "eevee_lightprobe_data")
     .image(0, GPU_RGBA16F, Qualifier::READ, ImageType::FLOAT_2D, "ray_data_img")
     .image(1, RAYTRACE_RAYTIME_FORMAT, Qualifier::WRITE, ImageType::FLOAT_2D, "ray_time_img")
     .image(2, RAYTRACE_RADIANCE_FORMAT, Qualifier::WRITE, ImageType::FLOAT_2D, "ray_radiance_img")
@@ -210,6 +214,7 @@ GPU_SHADER_CREATE_INFO(eevee_horizon_denoise)
     .additional_info("eevee_shared",
                      "eevee_gbuffer_data",
                      "eevee_global_ubo",
+                     "eevee_sampling_data",
                      "eevee_lightprobe_data",
                      "draw_view")
     .sampler(1, ImageType::DEPTH_2D, "depth_tx")