Eevee: Add Volume Transmittance to Color Render Passes.

In Cycles the volume transmittance is already composited into the color
passes. In Eevee the volume transmittance pass was separate and needed
to be composited in the compositor. This patch adds the volume
transmittance pass direct in the next render passes:

 * Diffuse Color
 * Specular Color
 * Emission
 * Environment

This patch includes the removal of the volume transmittance render pass.
It also renames the volume render passes to match Cycles. The setting
themselves aren't unified.

Maniphest Tasks: T81134

9 files changed, 90 insertions, 56 deletions

diff --git a/source/blender/blenloader/intern/versioning_290.c b/source/blender/blenloader/intern/versioning_290.c
index f390f0b48d8..fe22558eb06 100644
--- a/source/blender/blenloader/intern/versioning_290.c
+++ b/source/blender/blenloader/intern/versioning_290.c
@@ -1258,5 +1258,27 @@ void blo_do_versions_290(FileData *fd, Library *UNUSED(lib), Main *bmain)
         }
       }
     }
+
+    /* EEVEE/Cycles Volumes consistency */
+    for (Scene *scene = bmain->scenes.first; scene; scene = scene->id.next) {
+      /* Remove Volume Transmittance render pass from each view layer. */
+      LISTBASE_FOREACH (ViewLayer *, view_layer, &scene->view_layers) {
+        view_layer->eevee.render_passes &= ~EEVEE_RENDER_PASS_UNUSED_8;
+      }
+
+      /* Rename Renderlayer Socket `VolumeScatterCol` to `VolumeDir` */
+      if (scene->nodetree) {
+        LISTBASE_FOREACH (bNode *, node, &scene->nodetree->nodes) {
+          if (node->type == CMP_NODE_R_LAYERS) {
+            LISTBASE_FOREACH (bNodeSocket *, output_socket, &node->outputs) {
+              const static char *volume_scatter = "VolumeScatterCol";
+              if (STREQLEN(output_socket->name, volume_scatter, MAX_NAME)) {
+                BLI_strncpy(output_socket->name, RE_PASSNAME_VOLUME_LIGHT, MAX_NAME);
+              }
+            }
+          }
+        }
+      }
+    }
   }
 }
diff --git a/source/blender/draw/engines/eevee/eevee_private.h b/source/blender/draw/engines/eevee/eevee_private.h
index a6a480ca967..5bf8cab1b22 100644
--- a/source/blender/draw/engines/eevee/eevee_private.h
+++ b/source/blender/draw/engines/eevee/eevee_private.h
@@ -989,6 +989,7 @@ typedef struct EEVEE_PrivateData {
   GPUTexture *renderpass_input;
   GPUTexture *renderpass_col_input;
   GPUTexture *renderpass_light_input;
+  GPUTexture *renderpass_transmittance_input;
   /* Renderpass ubo reference used by material pass. */
   struct GPUUniformBuf *renderpass_ubo;
   /** For rendering shadows. */
diff --git a/source/blender/draw/engines/eevee/eevee_render.c b/source/blender/draw/engines/eevee/eevee_render.c
index 2b2ff2e5c90..2a01aeefce8 100644
--- a/source/blender/draw/engines/eevee/eevee_render.c
+++ b/source/blender/draw/engines/eevee/eevee_render.c
@@ -461,21 +461,13 @@ static void eevee_render_result_environment(RenderLayer *rl,
   EEVEE_RENDER_RESULT_MATERIAL_PASS(ENVIRONMENT, ENVIRONMENT)
 }
 
-static void eevee_render_result_volume_scatter(RenderLayer *rl,
-                                               const char *viewname,
-                                               const rcti *rect,
-                                               EEVEE_Data *vedata,
-                                               EEVEE_ViewLayerData *sldata)
-{
-  EEVEE_RENDER_RESULT_MATERIAL_PASS(VOLUME_SCATTER, VOLUME_SCATTER)
-}
-static void eevee_render_result_volume_transmittance(RenderLayer *rl,
-                                                     const char *viewname,
-                                                     const rcti *rect,
-                                                     EEVEE_Data *vedata,
-                                                     EEVEE_ViewLayerData *sldata)
+static void eevee_render_result_volume_light(RenderLayer *rl,
+                                             const char *viewname,
+                                             const rcti *rect,
+                                             EEVEE_Data *vedata,
+                                             EEVEE_ViewLayerData *sldata)
 {
-  EEVEE_RENDER_RESULT_MATERIAL_PASS(VOLUME_TRANSMITTANCE, VOLUME_TRANSMITTANCE)
+  EEVEE_RENDER_RESULT_MATERIAL_PASS(VOLUME_LIGHT, VOLUME_LIGHT)
 }
 
 static void eevee_render_result_aovs(RenderLayer *rl,
@@ -696,8 +688,7 @@ void EEVEE_render_read_result(EEVEE_Data *vedata,
   eevee_render_result_emission(rl, viewname, rect, vedata, sldata);
   eevee_render_result_environment(rl, viewname, rect, vedata, sldata);
   eevee_render_result_bloom(rl, viewname, rect, vedata, sldata);
-  eevee_render_result_volume_scatter(rl, viewname, rect, vedata, sldata);
-  eevee_render_result_volume_transmittance(rl, viewname, rect, vedata, sldata);
+  eevee_render_result_volume_light(rl, viewname, rect, vedata, sldata);
   eevee_render_result_aovs(rl, viewname, rect, vedata, sldata);
   eevee_render_result_cryptomatte(rl, viewname, rect, vedata, sldata);
 }
@@ -730,8 +721,7 @@ void EEVEE_render_update_passes(RenderEngine *engine, Scene *scene, ViewLayer *v
   CHECK_PASS_LEGACY(GLOSSY_DIRECT, SOCK_RGBA, 3, "RGB");
   CHECK_PASS_LEGACY(EMIT, SOCK_RGBA, 3, "RGB");
   CHECK_PASS_LEGACY(ENVIRONMENT, SOCK_RGBA, 3, "RGB");
-  CHECK_PASS_EEVEE(VOLUME_SCATTER, SOCK_RGBA, 3, "RGB");
-  CHECK_PASS_EEVEE(VOLUME_TRANSMITTANCE, SOCK_RGBA, 3, "RGB");
+  CHECK_PASS_EEVEE(VOLUME_LIGHT, SOCK_RGBA, 3, "RGB");
   CHECK_PASS_EEVEE(BLOOM, SOCK_RGBA, 3, "RGB");
 
   LISTBASE_FOREACH (ViewLayerAOV *, aov, &view_layer->aovs) {
diff --git a/source/blender/draw/engines/eevee/eevee_renderpasses.c b/source/blender/draw/engines/eevee/eevee_renderpasses.c
index e7a03c678a8..6f87ff302f4 100644
--- a/source/blender/draw/engines/eevee/eevee_renderpasses.c
+++ b/source/blender/draw/engines/eevee/eevee_renderpasses.c
@@ -44,14 +44,14 @@ typedef enum eRenderPassPostProcessType {
   PASS_POST_AO = 6,
   PASS_POST_NORMAL = 7,
   PASS_POST_TWO_LIGHT_BUFFERS = 8,
+  PASS_POST_ACCUMULATED_TRANSMITTANCE_COLOR = 9,
 } eRenderPassPostProcessType;
 
 /* bitmask containing all renderpasses that need post-processing */
 #define EEVEE_RENDERPASSES_WITH_POST_PROCESSING \
   (EEVEE_RENDER_PASS_Z | EEVEE_RENDER_PASS_MIST | EEVEE_RENDER_PASS_NORMAL | \
-   EEVEE_RENDER_PASS_AO | EEVEE_RENDER_PASS_BLOOM | EEVEE_RENDER_PASS_VOLUME_SCATTER | \
-   EEVEE_RENDER_PASS_VOLUME_TRANSMITTANCE | EEVEE_RENDER_PASS_SHADOW | \
-   EEVEE_RENDERPASSES_MATERIAL)
+   EEVEE_RENDER_PASS_AO | EEVEE_RENDER_PASS_BLOOM | EEVEE_RENDER_PASS_VOLUME_LIGHT | \
+   EEVEE_RENDER_PASS_SHADOW | EEVEE_RENDERPASSES_MATERIAL)
 
 #define EEVEE_RENDERPASSES_ALL \
   (EEVEE_RENDERPASSES_WITH_POST_PROCESSING | EEVEE_RENDER_PASS_COMBINED)
@@ -64,7 +64,10 @@ typedef enum eRenderPassPostProcessType {
    EEVEE_RENDER_PASS_BLOOM)
 #define EEVEE_RENDERPASSES_LIGHT_PASS \
   (EEVEE_RENDER_PASS_DIFFUSE_LIGHT | EEVEE_RENDER_PASS_SPECULAR_LIGHT)
-
+/* Render passes that uses volume transmittance when available */
+#define EEVEE_RENDERPASSES_USES_TRANSMITTANCE \
+  (EEVEE_RENDER_PASS_DIFFUSE_COLOR | EEVEE_RENDER_PASS_SPECULAR_COLOR | EEVEE_RENDER_PASS_EMIT | \
+   EEVEE_RENDER_PASS_ENVIRONMENT)
 bool EEVEE_renderpasses_only_first_sample_pass_active(EEVEE_Data *vedata)
 {
   EEVEE_StorageList *stl = vedata->stl;
@@ -147,6 +150,18 @@ void EEVEE_renderpasses_init(EEVEE_Data *vedata)
   EEVEE_cryptomatte_renderpasses_init(vedata);
 }
 
+BLI_INLINE bool eevee_renderpasses_volumetric_active(const EEVEE_EffectsInfo *effects,
+                                                     const EEVEE_PrivateData *g_data)
+{
+  if (effects->enabled_effects & EFFECT_VOLUMETRIC) {
+    if (g_data->render_passes &
+        (EEVEE_RENDER_PASS_VOLUME_LIGHT | EEVEE_RENDERPASSES_USES_TRANSMITTANCE)) {
+      return true;
+    }
+  }
+  return false;
+}
+
 void EEVEE_renderpasses_output_init(EEVEE_ViewLayerData *sldata,
                                     EEVEE_Data *vedata,
                                     uint tot_samples)
@@ -189,8 +204,7 @@ void EEVEE_renderpasses_output_init(EEVEE_ViewLayerData *sldata,
       EEVEE_bloom_output_init(sldata, vedata, tot_samples);
     }
 
-    if ((g_data->render_passes &
-         (EEVEE_RENDER_PASS_VOLUME_TRANSMITTANCE | EEVEE_RENDER_PASS_VOLUME_SCATTER)) != 0) {
+    if (eevee_renderpasses_volumetric_active(effects, g_data)) {
       EEVEE_volumes_output_init(sldata, vedata, tot_samples);
     }
 
@@ -198,6 +212,7 @@ void EEVEE_renderpasses_output_init(EEVEE_ViewLayerData *sldata,
     g_data->renderpass_input = txl->color;
     g_data->renderpass_col_input = txl->color;
     g_data->renderpass_light_input = txl->color;
+    g_data->renderpass_transmittance_input = txl->color;
   }
   else {
     /* Free unneeded memory */
@@ -227,6 +242,8 @@ void EEVEE_renderpasses_cache_finish(EEVEE_ViewLayerData *sldata, EEVEE_Data *ve
     DRW_shgroup_uniform_texture_ref(grp, "inputColorBuffer", &g_data->renderpass_col_input);
     DRW_shgroup_uniform_texture_ref(
         grp, "inputSecondLightBuffer", &g_data->renderpass_light_input);
+    DRW_shgroup_uniform_texture_ref(
+        grp, "inputTransmittanceBuffer", &g_data->renderpass_transmittance_input);
     DRW_shgroup_uniform_texture_ref(grp, "depthBuffer", &dtxl->depth);
     DRW_shgroup_uniform_block_ref(grp, "common_block", &sldata->common_ubo);
     DRW_shgroup_uniform_block_ref(grp, "renderpass_block", &sldata->renderpass_ubo.combined);
@@ -265,6 +282,20 @@ void EEVEE_renderpasses_postprocess(EEVEE_ViewLayerData *UNUSED(sldata),
   g_data->renderpass_current_sample = current_sample;
   g_data->renderpass_type = renderpass_type;
   g_data->renderpass_postprocess = PASS_POST_UNDEFINED;
+  const bool volumetric_active = eevee_renderpasses_volumetric_active(effects, g_data);
+  eViewLayerEEVEEPassType default_color_pass_type = volumetric_active ?
+                                                        PASS_POST_ACCUMULATED_TRANSMITTANCE_COLOR :
+                                                        PASS_POST_ACCUMULATED_COLOR;
+  g_data->renderpass_transmittance_input = volumetric_active ? txl->volume_transmittance_accum :
+                                                               txl->color;
+
+  if (!volumetric_active && renderpass_type == EEVEE_RENDER_PASS_VOLUME_LIGHT) {
+    /* Early exit: Volumetric effect is off, but the volume light pass was requested. */
+    static float clear_col[4] = {0.0f};
+    GPU_framebuffer_bind(fbl->renderpass_fb);
+    GPU_framebuffer_clear_color(fbl->renderpass_fb, clear_col);
+    return;
+  }
 
   switch (renderpass_type) {
     case EEVEE_RENDER_PASS_Z: {
@@ -286,38 +317,33 @@ void EEVEE_renderpasses_postprocess(EEVEE_ViewLayerData *UNUSED(sldata),
       g_data->renderpass_input = txl->mist_accum;
       break;
     }
-    case EEVEE_RENDER_PASS_VOLUME_SCATTER: {
+    case EEVEE_RENDER_PASS_VOLUME_LIGHT: {
       g_data->renderpass_postprocess = PASS_POST_ACCUMULATED_COLOR;
       g_data->renderpass_input = txl->volume_scatter_accum;
       break;
     }
-    case EEVEE_RENDER_PASS_VOLUME_TRANSMITTANCE: {
-      g_data->renderpass_postprocess = PASS_POST_ACCUMULATED_COLOR;
-      g_data->renderpass_input = txl->volume_transmittance_accum;
-      break;
-    }
     case EEVEE_RENDER_PASS_SHADOW: {
       g_data->renderpass_postprocess = PASS_POST_ACCUMULATED_VALUE;
       g_data->renderpass_input = txl->shadow_accum;
       break;
     }
     case EEVEE_RENDER_PASS_DIFFUSE_COLOR: {
-      g_data->renderpass_postprocess = PASS_POST_ACCUMULATED_COLOR;
+      g_data->renderpass_postprocess = default_color_pass_type;
       g_data->renderpass_input = txl->diff_color_accum;
       break;
     }
     case EEVEE_RENDER_PASS_SPECULAR_COLOR: {
-      g_data->renderpass_postprocess = PASS_POST_ACCUMULATED_COLOR;
+      g_data->renderpass_postprocess = default_color_pass_type;
       g_data->renderpass_input = txl->spec_color_accum;
       break;
     }
     case EEVEE_RENDER_PASS_ENVIRONMENT: {
-      g_data->renderpass_postprocess = PASS_POST_ACCUMULATED_COLOR;
+      g_data->renderpass_postprocess = default_color_pass_type;
       g_data->renderpass_input = txl->env_accum;
       break;
     }
     case EEVEE_RENDER_PASS_EMIT: {
-      g_data->renderpass_postprocess = PASS_POST_ACCUMULATED_COLOR;
+      g_data->renderpass_postprocess = default_color_pass_type;
       g_data->renderpass_input = txl->emit_accum;
       break;
     }
@@ -372,7 +398,8 @@ void EEVEE_renderpasses_output_accumulate(EEVEE_ViewLayerData *sldata,
 {
   EEVEE_StorageList *stl = vedata->stl;
   EEVEE_EffectsInfo *effects = stl->effects;
-  eViewLayerEEVEEPassType render_pass = stl->g_data->render_passes;
+  EEVEE_PrivateData *g_data = stl->g_data;
+  eViewLayerEEVEEPassType render_pass = g_data->render_passes;
 
   if (!post_effect) {
     if ((render_pass & EEVEE_RENDER_PASS_MIST) != 0) {
@@ -387,8 +414,7 @@ void EEVEE_renderpasses_output_accumulate(EEVEE_ViewLayerData *sldata,
     if ((render_pass & EEVEE_RENDERPASSES_MATERIAL) != 0) {
       EEVEE_material_output_accumulate(sldata, vedata);
     }
-    if ((render_pass &
-         (EEVEE_RENDER_PASS_VOLUME_TRANSMITTANCE | EEVEE_RENDER_PASS_VOLUME_SCATTER)) != 0) {
+    if (eevee_renderpasses_volumetric_active(effects, g_data)) {
       EEVEE_volumes_output_accumulate(sldata, vedata);
     }
     if ((render_pass & EEVEE_RENDER_PASS_CRYPTOMATTE) != 0) {
diff --git a/source/blender/draw/engines/eevee/shaders/renderpass_postprocess_frag.glsl b/source/blender/draw/engines/eevee/shaders/renderpass_postprocess_frag.glsl
index eb6ca4b9de8..0bbbe58c44a 100644
--- a/source/blender/draw/engines/eevee/shaders/renderpass_postprocess_frag.glsl
+++ b/source/blender/draw/engines/eevee/shaders/renderpass_postprocess_frag.glsl
@@ -11,6 +11,7 @@
 #define PASS_POST_AO 6
 #define PASS_POST_NORMAL 7
 #define PASS_POST_TWO_LIGHT_BUFFERS 8
+#define PASS_POST_ACCUMULATED_TRANSMITTANCE_COLOR 9
 
 uniform int postProcessType;
 uniform int currentSample;
@@ -19,6 +20,7 @@ uniform sampler2D depthBuffer;
 uniform sampler2D inputBuffer;
 uniform sampler2D inputSecondLightBuffer;
 uniform sampler2D inputColorBuffer;
+uniform sampler2D inputTransmittanceBuffer;
 
 out vec4 fragColor;
 
@@ -99,6 +101,11 @@ void main()
     vec4 accumulated_color = texelFetch(inputBuffer, texel, 0);
     color = (accumulated_color / currentSample);
   }
+  else if (postProcessType == PASS_POST_ACCUMULATED_TRANSMITTANCE_COLOR) {
+    vec3 accumulated_color = texelFetch(inputBuffer, texel, 0).rgb;
+    vec3 transmittance = texelFetch(inputTransmittanceBuffer, texel, 0).rgb;
+    color.rgb = (accumulated_color / currentSample) * (transmittance / currentSample);
+  }
   else if (postProcessType == PASS_POST_ACCUMULATED_LIGHT) {
     vec3 accumulated_light = texelFetch(inputBuffer, texel, 0).rgb;
     vec3 accumulated_color = texelFetch(inputColorBuffer, texel, 0).rgb;
diff --git a/source/blender/makesdna/DNA_layer_types.h b/source/blender/makesdna/DNA_layer_types.h
index 6a91f4857b4..828c6ff2a51 100644
--- a/source/blender/makesdna/DNA_layer_types.h
+++ b/source/blender/makesdna/DNA_layer_types.h
@@ -40,8 +40,8 @@ typedef enum eViewLayerEEVEEPassType {
   EEVEE_RENDER_PASS_DIFFUSE_COLOR = (1 << 5),
   EEVEE_RENDER_PASS_SPECULAR_LIGHT = (1 << 6),
   EEVEE_RENDER_PASS_SPECULAR_COLOR = (1 << 7),
-  EEVEE_RENDER_PASS_VOLUME_TRANSMITTANCE = (1 << 8),
-  EEVEE_RENDER_PASS_VOLUME_SCATTER = (1 << 9),
+  EEVEE_RENDER_PASS_UNUSED_8 = (1 << 8),
+  EEVEE_RENDER_PASS_VOLUME_LIGHT = (1 << 9),
   EEVEE_RENDER_PASS_EMIT = (1 << 10),
   EEVEE_RENDER_PASS_ENVIRONMENT = (1 << 11),
   EEVEE_RENDER_PASS_SHADOW = (1 << 12),
diff --git a/source/blender/makesdna/DNA_scene_types.h b/source/blender/makesdna/DNA_scene_types.h
index 85ec3dfdced..06f7f7aafb4 100644
--- a/source/blender/makesdna/DNA_scene_types.h
+++ b/source/blender/makesdna/DNA_scene_types.h
@@ -323,8 +323,7 @@ typedef enum eScenePassType {
 
 #define RE_PASSNAME_FREESTYLE "Freestyle"
 #define RE_PASSNAME_BLOOM "BloomCol"
-#define RE_PASSNAME_VOLUME_TRANSMITTANCE "VolumeTransmCol"
-#define RE_PASSNAME_VOLUME_SCATTER "VolumeScatterCol"
+#define RE_PASSNAME_VOLUME_LIGHT "VolumeDir"
 
 /* View - MultiView */
 typedef struct SceneRenderView {
diff --git a/source/blender/makesrna/intern/rna_scene.c b/source/blender/makesrna/intern/rna_scene.c
index d418614d7a0..72c6fda86cd 100644
--- a/source/blender/makesrna/intern/rna_scene.c
+++ b/source/blender/makesrna/intern/rna_scene.c
@@ -3995,15 +3995,9 @@ static void rna_def_view_layer_eevee(BlenderRNA *brna)
   srna = RNA_def_struct(brna, "ViewLayerEEVEE", NULL);
   RNA_def_struct_ui_text(srna, "Eevee Settings", "View layer settings for Eevee");
 
-  prop = RNA_def_property(srna, "use_pass_volume_scatter", PROP_BOOLEAN, PROP_NONE);
-  RNA_def_property_boolean_sdna(prop, NULL, "render_passes", EEVEE_RENDER_PASS_VOLUME_SCATTER);
-  RNA_def_property_ui_text(prop, "Volume Scatter", "Deliver volume scattering pass");
-  RNA_def_property_update(prop, NC_SCENE | ND_RENDER_OPTIONS, "rna_ViewLayer_pass_update");
-
-  prop = RNA_def_property(srna, "use_pass_volume_transmittance", PROP_BOOLEAN, PROP_NONE);
-  RNA_def_property_boolean_sdna(
-      prop, NULL, "render_passes", EEVEE_RENDER_PASS_VOLUME_TRANSMITTANCE);
-  RNA_def_property_ui_text(prop, "Volume Transmittance", "Deliver volume transmittance pass");
+  prop = RNA_def_property(srna, "use_pass_volume_direct", PROP_BOOLEAN, PROP_NONE);
+  RNA_def_property_boolean_sdna(prop, NULL, "render_passes", EEVEE_RENDER_PASS_VOLUME_LIGHT);
+  RNA_def_property_ui_text(prop, "Volume Light", "Deliver volume direct light pass");
   RNA_def_property_update(prop, NC_SCENE | ND_RENDER_OPTIONS, "rna_ViewLayer_pass_update");
 
   prop = RNA_def_property(srna, "use_pass_bloom", PROP_BOOLEAN, PROP_NONE);
diff --git a/source/blender/makesrna/intern/rna_space.c b/source/blender/makesrna/intern/rna_space.c
index d0afebe5465..36dbb1c78cc 100644
--- a/source/blender/makesrna/intern/rna_space.c
+++ b/source/blender/makesrna/intern/rna_space.c
@@ -412,12 +412,7 @@ static const EnumPropertyItem rna_enum_view3dshading_render_pass_type_items[] =
     {EEVEE_RENDER_PASS_DIFFUSE_COLOR, "DIFFUSE_COLOR", 0, "Diffuse Color", ""},
     {EEVEE_RENDER_PASS_SPECULAR_LIGHT, "SPECULAR_LIGHT", 0, "Specular Light", ""},
     {EEVEE_RENDER_PASS_SPECULAR_COLOR, "SPECULAR_COLOR", 0, "Specular Color", ""},
-    {EEVEE_RENDER_PASS_VOLUME_TRANSMITTANCE,
-     "VOLUME_TRANSMITTANCE",
-     0,
-     "Volume Transmittance",
-     ""},
-    {EEVEE_RENDER_PASS_VOLUME_SCATTER, "VOLUME_SCATTER", 0, "Volume Scattering", ""},
+    {EEVEE_RENDER_PASS_VOLUME_LIGHT, "VOLUME_LIGHT", 0, "Volume Light", ""},
 
     {0, "", ICON_NONE, "Effects", ""},
     {EEVEE_RENDER_PASS_BLOOM, "BLOOM", 0, "Bloom", ""},