Sculpt: Grab silhouette option

This adds a property to the grab that masks vertices based on its
original normal and grab delta. When used on thin meshes, it allows to
grab the silhouette from one side of the object without affecting the
shape of the other side.

Reviewed By: sergey

Differential Revision: https://developer.blender.org/D9205

3 files changed, 29 insertions, 9 deletions

diff --git a/source/blender/editors/sculpt_paint/sculpt.c b/source/blender/editors/sculpt_paint/sculpt.c
index 3ffa2091560..8e7935e821d 100644
--- a/source/blender/editors/sculpt_paint/sculpt.c
+++ b/source/blender/editors/sculpt_paint/sculpt.c
@@ -3805,20 +3805,33 @@ static void do_grab_brush_task_cb_ex(void *__restrict userdata,
       ss, &test, data->brush->falloff_shape);
   const int thread_id = BLI_task_parallel_thread_id(tls);
 
+  const bool grab_silhouette = brush->flag2 & BRUSH_GRAB_SILHOUETTE;
+
   BKE_pbvh_vertex_iter_begin(ss->pbvh, data->nodes[n], vd, PBVH_ITER_UNIQUE)
   {
     SCULPT_orig_vert_data_update(&orig_data, &vd);
 
     if (sculpt_brush_test_sq_fn(&test, orig_data.co)) {
-      const float fade = bstrength * SCULPT_brush_strength_factor(ss,
-                                                                  brush,
-                                                                  orig_data.co,
-                                                                  sqrtf(test.dist),
-                                                                  orig_data.no,
-                                                                  NULL,
-                                                                  vd.mask ? *vd.mask : 0.0f,
-                                                                  vd.index,
-                                                                  thread_id);
+      float fade = bstrength * SCULPT_brush_strength_factor(ss,
+                                                            brush,
+                                                            orig_data.co,
+                                                            sqrtf(test.dist),
+                                                            orig_data.no,
+                                                            NULL,
+                                                            vd.mask ? *vd.mask : 0.0f,
+                                                            vd.index,
+                                                            thread_id);
+
+      if (grab_silhouette) {
+        float silhouette_test_dir[3];
+        normalize_v3_v3(silhouette_test_dir, grab_delta);
+        if (dot_v3v3(ss->cache->initial_normal, ss->cache->grab_delta) < 0.0f) {
+          mul_v3_fl(silhouette_test_dir, -1.0f);
+        }
+        float vno[3];
+        normal_short_to_float_v3(vno, orig_data.no);
+        fade *= max_ff(dot_v3v3(vno, silhouette_test_dir), 0.0f);
+      }
 
       mul_v3_v3fl(proxy[vd.i], grab_delta, fade);
 
diff --git a/source/blender/makesdna/DNA_brush_types.h b/source/blender/makesdna/DNA_brush_types.h
index 37b7947dbea..713f5ee2afa 100644
--- a/source/blender/makesdna/DNA_brush_types.h
+++ b/source/blender/makesdna/DNA_brush_types.h
@@ -775,6 +775,7 @@ typedef enum eBrushFlags2 {
   BRUSH_POSE_USE_LOCK_ROTATION = (1 << 5),
   BRUSH_CLOTH_USE_COLLISION = (1 << 6),
   BRUSH_AREA_RADIUS_PRESSURE = (1 << 7),
+  BRUSH_GRAB_SILHOUETTE = (1 << 8),
 } eBrushFlags2;
 
 typedef enum {
diff --git a/source/blender/makesrna/intern/rna_brush.c b/source/blender/makesrna/intern/rna_brush.c
index d119be66916..6f227ec210c 100644
--- a/source/blender/makesrna/intern/rna_brush.c
+++ b/source/blender/makesrna/intern/rna_brush.c
@@ -2968,6 +2968,12 @@ static void rna_def_brush(BlenderRNA *brna)
       "Apply the maximum grab strength to the active vertex instead of the cursor location");
   RNA_def_property_update(prop, 0, "rna_Brush_update");
 
+  prop = RNA_def_property(srna, "use_grab_silhouette", PROP_BOOLEAN, PROP_NONE);
+  RNA_def_property_boolean_sdna(prop, NULL, "flag2", BRUSH_GRAB_SILHOUETTE);
+  RNA_def_property_ui_text(
+      prop, "Grab Silhouette", "Grabs trying to automask the silhouette of the object");
+  RNA_def_property_update(prop, 0, "rna_Brush_update");
+
   prop = RNA_def_property(srna, "use_paint_antialiasing", PROP_BOOLEAN, PROP_NONE);
   RNA_def_property_boolean_sdna(prop, NULL, "sampling_flag", BRUSH_PAINT_ANTIALIASING);
   RNA_def_property_ui_text(prop, "Anti-Aliasing", "Smooths the edges of the strokes");