Face Sets: Use white color for a default Face Set to enable the overlay

This introduces a variable to store a face set ID which is going to be
rendered white. When initializing a mesh or randomizing the colors, this
variable gets updated to always render a white face set. This way the
face set overlay can be enabled without adding colors to the mesh if
face sets are not in use. After creating the first face set, new colors
are generated randomly like usual.

The face set stored as default does not have any special meaning for
tools or brushes, it just affects the rendering color.

Reviewed By: brecht

Differential Revision: https://developer.blender.org/D7035

1 files changed, 12 insertions, 4 deletions

diff --git a/source/blender/gpu/intern/gpu_buffers.c b/source/blender/gpu/intern/gpu_buffers.c
index 6671296db2a..5eae86e50f0 100644
--- a/source/blender/gpu/intern/gpu_buffers.c
+++ b/source/blender/gpu/intern/gpu_buffers.c
@@ -213,6 +213,7 @@ void GPU_pbvh_mesh_buffers_update(GPU_PBVH_Buffers *buffers,
                                   const MLoopCol *vcol,
                                   const int *sculpt_face_sets,
                                   const int face_sets_color_seed,
+                                  const int face_sets_color_default,
                                   const int (*face_vert_indices)[3],
                                   const int update_flags)
 {
@@ -267,8 +268,12 @@ void GPU_pbvh_mesh_buffers_update(GPU_PBVH_Buffers *buffers,
         for (uint i = 0; i < buffers->face_indices_len; i++) {
           if (show_face_sets) {
             const MLoopTri *lt = &buffers->looptri[buffers->face_indices[i]];
-            face_set_overlay_color_get(
-                sculpt_face_sets[lt->poly], face_sets_color_seed, face_set_color);
+            const int fset = abs(sculpt_face_sets[lt->poly]);
+
+            /* Skip for the default color Face Set to render it white. */
+            if (fset != face_sets_color_default) {
+              face_set_overlay_color_get(fset, face_sets_color_seed, face_set_color);
+            }
           }
           for (int j = 0; j < 3; j++) {
             const int vidx = face_vert_indices[i][j];
@@ -325,8 +330,11 @@ void GPU_pbvh_mesh_buffers_update(GPU_PBVH_Buffers *buffers,
 
           uchar face_set_color[4] = {UCHAR_MAX, UCHAR_MAX, UCHAR_MAX, UCHAR_MAX};
           if (show_face_sets) {
-            face_set_overlay_color_get(
-                sculpt_face_sets[lt->poly], face_sets_color_seed, face_set_color);
+            const int fset = abs(sculpt_face_sets[lt->poly]);
+            /* Skip for the default color Face Set to render it white. */
+            if (fset != face_sets_color_default) {
+              face_set_overlay_color_get(fset, face_sets_color_seed, face_set_color);
+            }
           }
 
           float fmask = 0.0f;