Fix T78369: Sculpt Vertex Colors not rendering in EEVEE

The vertex colors node was using the M_COL attribute type but Sculpt
Vertex Colors use CD_PROP_COLOR
Now the Vertex Color node also fallbacks to legacy vertex colors if
Scultp Vertex Colors are not enabled as experimental.

Reviewed By: brecht

Maniphest Tasks: T78369

Differential Revision: https://developer.blender.org/D8185

3 files changed, 24 insertions, 7 deletions

diff --git a/source/blender/draw/intern/draw_cache_impl_mesh.c b/source/blender/draw/intern/draw_cache_impl_mesh.c
index 40de0794b9e..e69fb795948 100644
--- a/source/blender/draw/intern/draw_cache_impl_mesh.c
+++ b/source/blender/draw/intern/draw_cache_impl_mesh.c
@@ -203,16 +203,17 @@ static DRW_MeshCDMask mesh_cd_calc_used_gpu_layers(const Mesh *me,
             type = CD_MTFACE;
 
             if (layer == -1) {
-              layer = CustomData_get_named_layer(cd_ldata, CD_MLOOPCOL, name);
-              type = CD_MCOL;
-            }
-
-            if (layer == -1) {
               if (U.experimental.use_sculpt_vertex_colors) {
                 layer = CustomData_get_named_layer(cd_vdata, CD_PROP_COLOR, name);
                 type = CD_PROP_COLOR;
               }
             }
+
+            if (layer == -1) {
+              layer = CustomData_get_named_layer(cd_ldata, CD_MLOOPCOL, name);
+              type = CD_MCOL;
+            }
+
 #if 0 /* Tangents are always from UV's - this will never happen. */
             if (layer == -1) {
               layer = CustomData_get_named_layer(cd_ldata, CD_TANGENT, name);
@@ -262,13 +263,26 @@ static DRW_MeshCDMask mesh_cd_calc_used_gpu_layers(const Mesh *me,
           }
           case CD_PROP_COLOR: {
             /* Sculpt Vertex Colors */
+            bool use_mloop_cols = false;
             if (layer == -1) {
               layer = (name[0] != '\0') ?
                           CustomData_get_named_layer(cd_vdata, CD_PROP_COLOR, name) :
                           CustomData_get_render_layer(cd_vdata, CD_PROP_COLOR);
+              /* Fallback to Vertex Color data */
+              if (layer == -1) {
+                layer = (name[0] != '\0') ?
+                            CustomData_get_named_layer(cd_ldata, CD_MLOOPCOL, name) :
+                            CustomData_get_render_layer(cd_ldata, CD_MLOOPCOL);
+                use_mloop_cols = true;
+              }
             }
             if (layer != -1) {
-              cd_used.sculpt_vcol |= (1 << layer);
+              if (use_mloop_cols) {
+                cd_used.vcol |= (1 << layer);
+              }
+              else {
+                cd_used.sculpt_vcol |= (1 << layer);
+              }
             }
             break;
           }
diff --git a/source/blender/editors/space_node/drawnode.c b/source/blender/editors/space_node/drawnode.c
index 780c3d6a217..695214bcc2f 100644
--- a/source/blender/editors/space_node/drawnode.c
+++ b/source/blender/editors/space_node/drawnode.c
@@ -1015,7 +1015,8 @@ static void node_shader_buts_vertex_color(uiLayout *layout, bContext *C, Pointer
   if (obptr.data && RNA_enum_get(&obptr, "type") == OB_MESH) {
     PointerRNA dataptr = RNA_pointer_get(&obptr, "data");
 
-    if (RNA_collection_length(&dataptr, "sculpt_vertex_colors")) {
+    if (U.experimental.use_sculpt_vertex_colors &&
+        RNA_collection_length(&dataptr, "sculpt_vertex_colors")) {
       uiItemPointerR(
           layout, ptr, "layer_name", &dataptr, "sculpt_vertex_colors", "", ICON_GROUP_VCOL);
     }
diff --git a/source/blender/gpu/intern/gpu_codegen.c b/source/blender/gpu/intern/gpu_codegen.c
index c1e7933d7ba..0a1d6f560b6 100644
--- a/source/blender/gpu/intern/gpu_codegen.c
+++ b/source/blender/gpu/intern/gpu_codegen.c
@@ -649,6 +649,8 @@ static const char *attr_prefix_get(CustomDataType type)
       return "t";
     case CD_MCOL:
       return "c";
+    case CD_PROP_COLOR:
+      return "c";
     case CD_AUTO_FROM_NAME:
       return "a";
     default: