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

@@ -137,6 +137,7 @@ void IrradianceCache::display_pass_draw(View &view, GPUFrameBuffer *view_fb)
     display_grids_ps_.push_constant("sphere_radius", 0.3f); /* TODO property */
     display_grids_ps_.push_constant("grid_resolution", grid_size);
     display_grids_ps_.push_constant("grid_to_world", grid.object_to_world);
+    display_grids_ps_.push_constant("world_to_grid", grid.world_to_object);
 
     display_grids_ps_.bind_texture("irradiance_a_tx", &irradiance_a_tx_);
     display_grids_ps_.bind_texture("irradiance_b_tx", &irradiance_b_tx_);
@@ -281,6 +282,8 @@ void IrradianceBake::surfels_create(const Object &probe_object)
   dispatch_per_grid_sample_ = math::divide_ceil(grid_resolution, int3(IRRADIANCE_GRID_GROUP_SIZE));
   capture_info_buf_.irradiance_grid_size = grid_resolution;
   capture_info_buf_.irradiance_grid_local_to_world = grid_local_to_world;
+  capture_info_buf_.irradiance_grid_world_to_local_rotation = float4x4(
+      (invert(normalize(float3x3(grid_local_to_world)))));
   capture_info_buf_.irradiance_accum_solid_angle = 0.0f;
   /* Divide by twice the sample count because each ray is evaluated in both directions. */
   capture_info_buf_.irradiance_sample_solid_angle = 4.0f * float(M_PI) /

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

@@ -29,6 +29,8 @@ void LightProbeModule::sync_grid(const Object *ob, ObjectHandle &handle)
     grid.initialized = true;
     grid.updated = true;
     grid.object_to_world = float4x4(ob->object_to_world);
+    grid.world_to_object = float4x4(
+        math::normalize(math::transpose(float3x3(grid.object_to_world))));
     grid.cache = ob->lightprobe_cache;
   }
 }

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

@@ -25,8 +25,10 @@ struct LightProbe {
 };
 
 struct IrradianceGrid : public LightProbe {
-  /** Reference to the light-cache data. Should be refreshed every sync. */
+  /** Copy of the transform matrix. */
   float4x4 object_to_world;
+  /** Precomputed inverse transform with normalized axes. No position. Used for rotating SH. */
+  float4x4 world_to_object;
   /**
    * Reference to the light-cache data.
    * Do not try to dereference it before LightProbeModule::end_sync() as the grid could

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

@@ -876,6 +876,9 @@ struct CaptureInfoData {
   float irradiance_accum_solid_angle;
   /** Transform of the lightprobe object. */
   float4x4 irradiance_grid_local_to_world;
+  /** Transform vectors from world space to local space. Does not have location component. */
+  /** TODO(fclem): This could be a float3x4 or a float3x3 if padded correctly. */
+  float4x4 irradiance_grid_world_to_local_rotation;
 };
 BLI_STATIC_ASSERT_ALIGN(CaptureInfoData, 16)
 

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

@@ -1,4 +1,5 @@
 #pragma BLENDER_REQUIRE(common_view_lib.glsl)
+#pragma BLENDER_REQUIRE(common_math_lib.glsl)
 #pragma BLENDER_REQUIRE(eevee_spherical_harmonics_lib.glsl)
 
 void main()
@@ -19,7 +20,8 @@ void main()
 
   vec3 vN = vec3(lP, sqrt(max(0.0, 1.0 - dist_sqr)));
   vec3 N = normal_view_to_world(vN);
+  vec3 lN = transform_direction(world_to_grid, N);
 
-  vec4 irradiance = spherical_harmonics_evaluate_lambert(N, sh);
+  vec4 irradiance = spherical_harmonics_evaluate_lambert(lN, sh);
   out_color = vec4(irradiance.rgb, 0.0);
 }

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

@@ -16,8 +16,10 @@
 
 void irradiance_capture(vec3 L, vec3 irradiance, inout SphericalHarmonicL1 sh)
 {
+  vec3 lL = transform_direction(capture_info_buf.irradiance_grid_world_to_local_rotation, L);
+
   spherical_harmonics_encode_signal_sample(
-      L, vec4(irradiance, 1.0) * capture_info_buf.irradiance_sample_solid_angle, sh);
+      lL, vec4(irradiance, 1.0) * capture_info_buf.irradiance_sample_solid_angle, sh);
 }
 
 void irradiance_capture(Surfel surfel_emitter, vec3 P, inout SphericalHarmonicL1 sh)

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

@@ -74,6 +74,7 @@ GPU_SHADER_CREATE_INFO(eevee_display_probe_grid)
     .push_constant(Type::FLOAT, "sphere_radius")
     .push_constant(Type::IVEC3, "grid_resolution")
     .push_constant(Type::MAT4, "grid_to_world")
+    .push_constant(Type::MAT4, "world_to_grid")
     .sampler(0, ImageType::FLOAT_3D, "irradiance_a_tx")
     .sampler(1, ImageType::FLOAT_3D, "irradiance_b_tx")
     .sampler(2, ImageType::FLOAT_3D, "irradiance_c_tx")