Fix T81254: Incorrect calculation of EEVEE Transmittance Volumetrics

Regular rendering uses a custom blend mode, but render passes renders to
2 separate textures. This wasn't configured correctly inside the
fragment shaders. This patch adds a switch to configure the fragment
shader with the correct attachments.

Backport to Blender 2.83.

Reviewed By: Clément Foucault

Differential Revision: https://developer.blender.org/D9038

1 files changed, 11 insertions, 7 deletions

diff --git a/source/blender/draw/engines/eevee/eevee_shaders.c b/source/blender/draw/engines/eevee/eevee_shaders.c
index 58897272425..f46a98ed845 100644
--- a/source/blender/draw/engines/eevee/eevee_shaders.c
+++ b/source/blender/draw/engines/eevee/eevee_shaders.c
@@ -137,7 +137,7 @@ static struct {
   struct GPUShader *scatter_sh;
   struct GPUShader *scatter_with_lights_sh;
   struct GPUShader *volumetric_integration_sh;
-  struct GPUShader *volumetric_resolve_sh;
+  struct GPUShader *volumetric_resolve_sh[2];
   struct GPUShader *volumetric_accum_sh;
 
   /* Shader strings */
@@ -854,13 +854,16 @@ struct GPUShader *EEVEE_shaders_volumes_integration_sh_get()
   return e_data.volumetric_integration_sh;
 }
 
-struct GPUShader *EEVEE_shaders_volumes_resolve_sh_get()
+struct GPUShader *EEVEE_shaders_volumes_resolve_sh_get(bool accum)
 {
-  if (e_data.volumetric_resolve_sh == NULL) {
-    e_data.volumetric_resolve_sh = DRW_shader_create_fullscreen_with_shaderlib(
-        datatoc_volumetric_resolve_frag_glsl, e_data.lib, SHADER_DEFINES);
+  const int index = accum ? 1 : 0;
+  if (e_data.volumetric_resolve_sh[index] == NULL) {
+    e_data.volumetric_resolve_sh[index] = DRW_shader_create_fullscreen_with_shaderlib(
+        datatoc_volumetric_resolve_frag_glsl,
+        e_data.lib,
+        accum ? "#define VOLUMETRICS_ACCUM\n" SHADER_DEFINES : SHADER_DEFINES);
   }
-  return e_data.volumetric_resolve_sh;
+  return e_data.volumetric_resolve_sh[index];
 }
 
 struct GPUShader *EEVEE_shaders_volumes_accum_sh_get()
@@ -1409,7 +1412,8 @@ void EEVEE_shaders_free(void)
   DRW_SHADER_FREE_SAFE(e_data.scatter_sh);
   DRW_SHADER_FREE_SAFE(e_data.scatter_with_lights_sh);
   DRW_SHADER_FREE_SAFE(e_data.volumetric_integration_sh);
-  DRW_SHADER_FREE_SAFE(e_data.volumetric_resolve_sh);
+  DRW_SHADER_FREE_SAFE(e_data.volumetric_resolve_sh[0]);
+  DRW_SHADER_FREE_SAFE(e_data.volumetric_resolve_sh[1]);
   DRW_SHADER_FREE_SAFE(e_data.volumetric_accum_sh);
   DRW_SHADER_FREE_SAFE(e_data.probe_filter_glossy_sh);
   DRW_SHADER_FREE_SAFE(e_data.probe_filter_diffuse_sh);