EEVEE-Next: Add compute shader to downsample sphere probe

This has no functional change except that it might speed
up probe updates since only updated pixels are processed.

Ref #118256

source/blender/draw/CMakeLists.txt

@@ -564,6 +564,7 @@ set(GLSL_SRC
   engines/eevee_next/shaders/eevee_ray_trace_screen_comp.glsl
   engines/eevee_next/shaders/eevee_ray_trace_screen_lib.glsl
   engines/eevee_next/shaders/eevee_ray_types_lib.glsl
+  engines/eevee_next/shaders/eevee_reflection_probe_convolve_comp.glsl
   engines/eevee_next/shaders/eevee_reflection_probe_eval_lib.glsl
   engines/eevee_next/shaders/eevee_reflection_probe_lib.glsl
   engines/eevee_next/shaders/eevee_reflection_probe_remap_comp.glsl

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

@@ -97,7 +97,7 @@ struct SphereProbeAtlasCoord {
   {
     SphereProbePixelArea coord;
     coord.extent = atlas_extent >> (subdivision_lvl + mip_lvl);
-    coord.offset = (area_location() * coord.extent) >> mip_lvl;
+    coord.offset = area_location() * coord.extent;
     coord.layer = atlas_layer;
     return coord;
   }

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

@@ -50,6 +50,17 @@ void SphereProbeModule::begin_sync()
     pass.push_constant("probe_brightness_clamp", probe_brightness_clamp);
     pass.dispatch(&dispatch_probe_pack_);
   }
+  {
+    PassSimple &pass = convolve_ps_;
+    pass.init();
+    pass.shader_set(instance_.shaders.static_shader_get(SPHERE_PROBE_CONVOLVE));
+    pass.bind_image("in_atlas_mip_img", &convolve_input_);
+    pass.bind_image("out_atlas_mip_img", &convolve_output_);
+    pass.push_constant("write_coord_packed", reinterpret_cast<int4 *>(&probe_write_coord_));
+    pass.barrier(GPU_BARRIER_SHADER_IMAGE_ACCESS);
+    pass.dispatch(&dispatch_probe_convolve_);
+    pass.barrier(GPU_BARRIER_SHADER_IMAGE_ACCESS);
+  }
   {
     PassSimple &pass = update_irradiance_ps_;
     pass.init();
@@ -85,6 +96,7 @@ bool SphereProbeModule::ensure_atlas()
                                  nullptr,
                                  SPHERE_PROBE_MIPMAP_LEVELS))
   {
+    probes_tx_.ensure_mip_views();
     /* TODO(fclem): Clearing means that we need to render all probes again.
      * If existing data exists, copy it using `CopyImageSubData`. */
     probes_tx_.clear(float4(0.0f));
@@ -187,8 +199,19 @@ void SphereProbeModule::remap_to_octahedral_projection(const SphereProbeAtlasCoo
   probe_write_coord_ = atlas_coord.as_write_coord(max_resolution_, 0);
   probe_mip_level_ = atlas_coord.subdivision_lvl;
   dispatch_probe_pack_ = int3(int2(ceil_division(resolution, SPHERE_PROBE_GROUP_SIZE)), 1);
-
   instance_.manager->submit(remap_ps_);
+
+  /* Populate the mip levels */
+  for (auto i : IndexRange(SPHERE_PROBE_MIPMAP_LEVELS - 1)) {
+    convolve_input_ = probes_tx_.mip_view(i);
+    convolve_output_ = probes_tx_.mip_view(i + 1);
+    probe_write_coord_ = atlas_coord.as_write_coord(max_resolution_, i + 1);
+    int out_mip_res = resolution >> (i + 1);
+    dispatch_probe_convolve_ = int3(int2(ceil_division(out_mip_res, SPHERE_PROBE_GROUP_SIZE)), 1);
+    instance_.manager->submit(convolve_ps_);
+  }
+  /* Sync with atlas usage for shading. */
+  GPU_memory_barrier(GPU_BARRIER_TEXTURE_FETCH);
 }
 
 void SphereProbeModule::update_world_irradiance()
@@ -198,11 +221,6 @@ void SphereProbeModule::update_world_irradiance()
   instance_.volume_probes.do_update_world_ = true;
 }
 
-void SphereProbeModule::update_probes_texture_mipmaps()
-{
-  GPU_texture_update_mipmap_chain(probes_tx_);
-}
-
 void SphereProbeModule::set_view(View & /*view*/)
 {
   Vector<SphereProbe *> probe_active;

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

@@ -53,9 +53,17 @@ class SphereProbeModule {
   PassSimple remap_ps_ = {"Probe.CubemapToOctahedral"};
   /** Extract irradiance information from the world. */
   PassSimple update_irradiance_ps_ = {"Probe.UpdateIrradiance"};
+  /** Copy volume probe irradiance for the center of sphere probes. */
   PassSimple select_ps_ = {"Probe.Select"};
+  /** Convolve the octahedral map to fill the Mip-map levels. */
+  PassSimple convolve_ps_ = {"Probe.Convolve"};
+  /** Input mip level for the convolution. */
+  GPUTexture *convolve_input_ = nullptr;
+  /** Output mip level for the convolution. */
+  GPUTexture *convolve_output_ = nullptr;
 
   int3 dispatch_probe_pack_ = int3(1);
+  int3 dispatch_probe_convolve_ = int3(1);
   int3 dispatch_probe_select_ = int3(1);
 
   /**
@@ -167,7 +175,6 @@ class SphereProbeModule {
    * Internal processing passes.
    */
   void remap_to_octahedral_projection(const SphereProbeAtlasCoord &atlas_coord);
-  void update_probes_texture_mipmaps();
   void update_world_irradiance();
 
   void sync_display(Vector<SphereProbe *> &probe_active);

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

@@ -214,6 +214,8 @@ const char *ShaderModule::static_shader_create_info_name_get(eShaderType shader_
       return "eevee_lightprobe_irradiance_ray";
     case LIGHTPROBE_IRRADIANCE_LOAD:
       return "eevee_lightprobe_irradiance_load";
+    case SPHERE_PROBE_CONVOLVE:
+      return "eevee_reflection_probe_convolve";
     case SPHERE_PROBE_REMAP:
       return "eevee_reflection_probe_remap";
     case SPHERE_PROBE_UPDATE_IRRADIANCE:

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

@@ -104,9 +104,10 @@ enum eShaderType {
   RAY_TRACE_PLANAR,
   RAY_TRACE_SCREEN,
 
+  SPHERE_PROBE_CONVOLVE,
   SPHERE_PROBE_REMAP,
-  SPHERE_PROBE_UPDATE_IRRADIANCE,
   SPHERE_PROBE_SELECT,
+  SPHERE_PROBE_UPDATE_IRRADIANCE,
 
   SHADOW_CLIPMAP_CLEAR,
   SHADOW_DEBUG,

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

@@ -263,7 +263,6 @@ void CaptureView::render_world()
     }
 
     inst_.sphere_probes.remap_to_octahedral_projection(update_info->atlas_coord);
-    inst_.sphere_probes.update_probes_texture_mipmaps();
   }
 
   if (update_info->do_world_irradiance_update) {
@@ -277,10 +276,8 @@ void CaptureView::render_probes()
 {
   Framebuffer prepass_fb;
   View view = {"Capture.View"};
-  bool do_update_mipmap_chain = false;
   while (const auto update_info = inst_.sphere_probes.probe_update_info_pop()) {
     GPU_debug_group_begin("Probe.Capture");
-    do_update_mipmap_chain = true;
 
     if (inst_.pipelines.data.is_probe_reflection != true) {
       inst_.pipelines.data.is_probe_reflection = true;
@@ -334,11 +331,6 @@ void CaptureView::render_probes()
     inst_.pipelines.data.is_probe_reflection = false;
     inst_.uniform_data.push_update();
   }
-
-  if (do_update_mipmap_chain) {
-    /* TODO: only update the regions that have been updated. */
-    inst_.sphere_probes.update_probes_texture_mipmaps();
-  }
 }
 
 /** \} */

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

@@ -0,0 +1,39 @@
+/* SPDX-FileCopyrightText: 2023 Blender Authors
+ *
+ * SPDX-License-Identifier: GPL-2.0-or-later */
+
+/* Shader to convert cube-map to octahedral projection. */
+
+#pragma BLENDER_REQUIRE(eevee_octahedron_lib.glsl)
+
+SphereProbePixelArea reinterpret_as_write_coord(ivec4 packed_coord)
+{
+  SphereProbePixelArea unpacked;
+  unpacked.offset = packed_coord.xy;
+  unpacked.extent = packed_coord.z;
+  unpacked.layer = packed_coord.w;
+  return unpacked;
+}
+
+void main()
+{
+  SphereProbePixelArea write_coord = reinterpret_as_write_coord(write_coord_packed);
+
+  /* Texel in probe. */
+  ivec2 local_texel = ivec2(gl_GlobalInvocationID.xy);
+
+  /* Exit when pixel being written doesn't fit in the area reserved for the probe. */
+  if (any(greaterThanEqual(local_texel, ivec2(write_coord.extent)))) {
+    return;
+  }
+
+  ivec2 texel_out = write_coord.offset + local_texel;
+  vec4 color = vec4(0.0);
+  color += imageLoad(in_atlas_mip_img, ivec3(texel_out * 2 + ivec2(0, 0), write_coord.layer));
+  color += imageLoad(in_atlas_mip_img, ivec3(texel_out * 2 + ivec2(1, 0), write_coord.layer));
+  color += imageLoad(in_atlas_mip_img, ivec3(texel_out * 2 + ivec2(0, 1), write_coord.layer));
+  color += imageLoad(in_atlas_mip_img, ivec3(texel_out * 2 + ivec2(1, 1), write_coord.layer));
+  color *= 0.25;
+
+  imageStore(out_atlas_mip_img, ivec3(texel_out, write_coord.layer), color);
+}

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

@@ -54,6 +54,15 @@ GPU_SHADER_CREATE_INFO(eevee_reflection_probe_select)
     .compute_source("eevee_reflection_probe_select_comp.glsl")
     .do_static_compilation(true);
 
+GPU_SHADER_CREATE_INFO(eevee_reflection_probe_convolve)
+    .local_group_size(SPHERE_PROBE_GROUP_SIZE, SPHERE_PROBE_GROUP_SIZE)
+    .additional_info("eevee_shared")
+    .push_constant(Type::IVEC4, "write_coord_packed")
+    .image(0, GPU_RGBA16F, Qualifier::READ, ImageType::FLOAT_2D_ARRAY, "in_atlas_mip_img")
+    .image(1, GPU_RGBA16F, Qualifier::WRITE, ImageType::FLOAT_2D_ARRAY, "out_atlas_mip_img")
+    .compute_source("eevee_reflection_probe_convolve_comp.glsl")
+    .do_static_compilation(true);
+
 GPU_SHADER_INTERFACE_INFO(eevee_display_probe_reflection_iface, "")
     .smooth(Type::VEC2, "lP")
     .flat(Type::INT, "probe_index");