Sculpt: Clay Strips Tip Roundness property

This patch allow to change the brush tip shape between a square and a
circle using a brush property.

After this change we are no longer testing the distance against a cube
(the Z axis is not used). I did not test this in depth, but if it does
not produce any artifacts I think we can keep it this way instead of
adding more complexity to the code.

In this new distance test the brush falloff is only applied on the
rounded parts of the square to avoid sharp artifacts in the
diagonals. Because of this, the round version is much softer than
the square one. The planned hardness property will fix this, but
this can also be avoided by setting the fallof to a custom curve.

Reviewed By: jbakker

Differential Revision: https://developer.blender.org/D6165

2 files changed, 32 insertions, 9 deletions

diff --git a/source/blender/editors/sculpt_paint/sculpt.c b/source/blender/editors/sculpt_paint/sculpt.c
index e0c75e1e64f..4fae136d133 100644
--- a/source/blender/editors/sculpt_paint/sculpt.c
+++ b/source/blender/editors/sculpt_paint/sculpt.c
@@ -1109,7 +1109,10 @@ bool sculpt_brush_test_circle_sq(SculptBrushTest *test, const float co[3])
   }
 }
 
-bool sculpt_brush_test_cube(SculptBrushTest *test, const float co[3], float local[4][4])
+bool sculpt_brush_test_cube(SculptBrushTest *test,
+                            const float co[3],
+                            float local[4][4],
+                            const float roundness)
 {
   float side = M_SQRT1_2;
   float local_co[3];
@@ -1124,14 +1127,32 @@ bool sculpt_brush_test_cube(SculptBrushTest *test, const float co[3], float loca
   local_co[1] = fabsf(local_co[1]);
   local_co[2] = fabsf(local_co[2]);
 
-  const float p = 8.0f;
-  if (local_co[0] <= side && local_co[1] <= side && local_co[2] <= side) {
-    test->dist = ((powf(local_co[0], p) + powf(local_co[1], p) + powf(local_co[2], p)) /
-                  powf(side, p));
+  /* Keep the square and circular brush tips the same size. */
+  side += (1.0f - side) * roundness;
+
+  const float hardness = 1.0f - roundness;
+  const float constant_side = hardness * side;
+  const float falloff_side = roundness * side;
 
+  if (local_co[0] <= side && local_co[1] <= side && local_co[2] <= side) {
+    /* Corner, distance to the center of the corner circle. */
+    if (min_ff(local_co[0], local_co[1]) > constant_side) {
+      float r_point[3];
+      copy_v3_fl(r_point, constant_side);
+      test->dist = len_v2v2(r_point, local_co) / falloff_side;
+      return true;
+    }
+    /* Side, distance to the square XY axis. */
+    if (max_ff(local_co[0], local_co[1]) > constant_side) {
+      test->dist = (max_ff(local_co[0], local_co[1]) - constant_side) / falloff_side;
+      return true;
+    }
+    /* Inside the square, constant distance. */
+    test->dist = 0.0f;
     return true;
   }
   else {
+    /* Outside the square. */
     return false;
   }
 }
@@ -5467,7 +5488,7 @@ static void do_clay_strips_brush_task_cb_ex(void *__restrict userdata,
 
   BKE_pbvh_vertex_iter_begin(ss->pbvh, data->nodes[n], vd, PBVH_ITER_UNIQUE)
   {
-    if (sculpt_brush_test_cube(&test, vd.co, mat)) {
+    if (sculpt_brush_test_cube(&test, vd.co, mat, brush->tip_roundness)) {
       if (plane_point_side_flip(vd.co, test.plane_tool, flip)) {
         float intr[3];
         float val[3];
@@ -7047,12 +7068,11 @@ static float sculpt_brush_dynamic_size_get(Brush *brush, StrokeCache *cache, flo
     case SCULPT_TOOL_CLAY:
       return max_ff(initial_size * 0.20f, initial_size * pow3f(cache->pressure));
     case SCULPT_TOOL_CLAY_STRIPS:
-      return max_ff(initial_size * 0.35f, initial_size * pow2f(cache->pressure));
+      return max_ff(initial_size * 0.30f, initial_size * pow2f(cache->pressure));
     case SCULPT_TOOL_CLAY_THUMB: {
       float clay_stabilized_pressure = sculpt_clay_thumb_get_stabilized_pressure(cache);
       return initial_size * clay_stabilized_pressure;
     }
-
     default:
       return initial_size * cache->pressure;
   }
diff --git a/source/blender/editors/sculpt_paint/sculpt_intern.h b/source/blender/editors/sculpt_paint/sculpt_intern.h
index 0b5bb942032..9d1795dec8f 100644
--- a/source/blender/editors/sculpt_paint/sculpt_intern.h
+++ b/source/blender/editors/sculpt_paint/sculpt_intern.h
@@ -280,7 +280,10 @@ void sculpt_brush_test_init(struct SculptSession *ss, SculptBrushTest *test);
 bool sculpt_brush_test_sphere(SculptBrushTest *test, const float co[3]);
 bool sculpt_brush_test_sphere_sq(SculptBrushTest *test, const float co[3]);
 bool sculpt_brush_test_sphere_fast(const SculptBrushTest *test, const float co[3]);
-bool sculpt_brush_test_cube(SculptBrushTest *test, const float co[3], float local[4][4]);
+bool sculpt_brush_test_cube(SculptBrushTest *test,
+                            const float co[3],
+                            float local[4][4],
+                            const float roundness);
 bool sculpt_brush_test_circle_sq(SculptBrushTest *test, const float co[3]);
 bool sculpt_search_sphere_cb(PBVHNode *node, void *data_v);
 bool sculpt_search_circle_cb(PBVHNode *node, void *data_v);