temp-sculpt-colors: Fix smear brush

Smear brush now:
* Walks two rings around vertices instead of one
* Accumulates a single weighted average instead of
  blending individually.
* Weights by how close vertices are to the desired smear
  distance, as well as their edge lengths (in the future
  edge length weighting will be replaced with either
  face areas or cotangent weights).

2 files changed, 68 insertions, 17 deletions

diff --git a/source/blender/draw/intern/draw_cache_impl_mesh.c b/source/blender/draw/intern/draw_cache_impl_mesh.c
index eb9a50493f0..2e1881b0346 100644
--- a/source/blender/draw/intern/draw_cache_impl_mesh.c
+++ b/source/blender/draw/intern/draw_cache_impl_mesh.c
@@ -868,7 +868,6 @@ static bool mesh_batch_cache_valid(Object *object, Mesh *me)
 
   if (object->sculpt && object->sculpt->pbvh) {
     if (cache->pbvh_is_drawing != BKE_pbvh_is_drawing(object->sculpt->pbvh)) {
-      printf("PBVH induced mesh cache invalidation!\n");
       return false;
     }
   }
diff --git a/source/blender/editors/sculpt_paint/sculpt_paint_color.c b/source/blender/editors/sculpt_paint/sculpt_paint_color.c
index 16d168ede08..66cb2fdca6f 100644
--- a/source/blender/editors/sculpt_paint/sculpt_paint_color.c
+++ b/source/blender/editors/sculpt_paint/sculpt_paint_color.c
@@ -393,6 +393,9 @@ static void do_smear_brush_task_cb_exec(void *__restrict userdata,
     float interp_color[4];
     copy_v4_v4(interp_color, ss->cache->prev_colors[vd.index]);
 
+    float no[3];
+    SCULPT_vertex_normal_get(ss, vd.index, no);
+
     switch (brush->smear_deform_type) {
       case BRUSH_SMEAR_DEFORM_DRAG:
         sub_v3_v3v3(current_disp, ss->cache->location, ss->cache->last_location);
@@ -404,27 +407,76 @@ static void do_smear_brush_task_cb_exec(void *__restrict userdata,
         sub_v3_v3v3(current_disp, vd.co, ss->cache->location);
         break;
     }
+
+    /* Project into vertex plane. */
+    madd_v3_v3fl(current_disp, no, -dot_v3v3(current_disp, no));
+
     normalize_v3_v3(current_disp_norm, current_disp);
     mul_v3_v3fl(current_disp, current_disp_norm, ss->cache->bstrength);
 
-    SculptVertexNeighborIter ni;
-    SCULPT_VERTEX_NEIGHBORS_ITER_BEGIN (ss, vd.index, ni) {
-      float vertex_disp[3];
-      float vertex_disp_norm[3];
-      sub_v3_v3v3(vertex_disp, SCULPT_vertex_co_get(ss, ni.index), vd.co);
-      const float *neighbor_color = ss->cache->prev_colors[ni.index];
-      normalize_v3_v3(vertex_disp_norm, vertex_disp);
-      if (dot_v3v3(current_disp_norm, vertex_disp_norm) >= 0.0f) {
-        continue;
+    float accum[4] = {0.0f, 0.0f, 0.0f, 0.0f};
+    float totw = 0.0f;
+
+    SculptVertexNeighborIter ni2;
+
+    SCULPT_VERTEX_NEIGHBORS_ITER_BEGIN (ss, vd.index, ni2) {
+      const float *nco = SCULPT_vertex_co_get(ss, ni2.index);
+
+      SculptVertexNeighborIter ni;
+      SCULPT_VERTEX_NEIGHBORS_ITER_BEGIN (ss, ni2.index, ni) {
+        if (ni.index == vd.index) {
+          continue;
+        }
+
+        float vertex_disp[3];
+        float vertex_disp_norm[3];
+
+        sub_v3_v3v3(vertex_disp, SCULPT_vertex_co_get(ss, ni.index), vd.co);
+
+        /* Weight by how close we are to our target distance from vd.co. */
+        float w = (1.0f + fabsf(len_v3(vertex_disp) / ss->cache->bstrength - 1.0));
+
+        /* TODO: use cotangents (or at least face areas) here. */
+        float len = len_v3v3(SCULPT_vertex_co_get(ss, ni.index), nco);
+        if (len > 0.0f) {
+          len = ss->cache->bstrength / len;
+        }
+        else { /* Coincident point. */
+          len = 1.0f;
+        }
+
+        /* Multiply weight with edge lengths (in the future this will be
+           cotangent weights or face areas). */
+        w *= len;
+
+        /* Build directional weight. */
+
+        /* Project into vertex plane. */
+        madd_v3_v3fl(vertex_disp, no, -dot_v3v3(no, vertex_disp));
+        normalize_v3_v3(vertex_disp_norm, vertex_disp);
+
+        if (dot_v3v3(current_disp_norm, vertex_disp_norm) >= 0.0f) {
+          continue;
+        }
+
+        const float *neighbor_color = ss->cache->prev_colors[ni.index];
+        float color_interp = -dot_v3v3(current_disp_norm, vertex_disp_norm);
+
+        /* Square directional weight to get a somewhat sharper result. */
+        w *= color_interp * color_interp;
+
+        madd_v4_v4fl(accum, neighbor_color, w);
+        totw += w;
       }
-      const float color_interp = clamp_f(
-          -dot_v3v3(current_disp_norm, vertex_disp_norm), 0.0f, 1.0f);
-      float color_mix[4];
-      copy_v4_v4(color_mix, neighbor_color);
-      mul_v4_fl(color_mix, color_interp * fade);
-      blend_color_mix_float(interp_color, interp_color, color_mix);
+      SCULPT_VERTEX_NEIGHBORS_ITER_END(ni);
     }
-    SCULPT_VERTEX_NEIGHBORS_ITER_END(ni);
+    SCULPT_VERTEX_NEIGHBORS_ITER_END(ni2);
+
+    if (totw != 0.0f) {
+      mul_v4_fl(accum, 1.0f / totw);
+    }
+
+    blend_color_mix_float(interp_color, interp_color, accum);
 
     float col[4];
     SCULPT_vertex_color_get(ss, vd.index, col);