Vertex Paint: projection options

This makes vertex paint match image painting more closely.

- Add falloff shape option sphere/circle
  where sphere uses a 3D radius around the cursor and
  circle uses a 2D radius (projected), like previous releases.
- Add normal angle option so you can control the falloff.
- Add Cull option, to paint onto faces pointing away.

Disabling normals, culling and using circle falloff
allows you to paint through the mesh.

source/blender/blenkernel/BKE_brush.h

@@ -70,7 +70,7 @@ void BKE_brush_randomize_texture_coords(struct UnifiedPaintSettings *ups, bool m
 /* brush curve */
 void BKE_brush_curve_preset(struct Brush *b, int preset);
 float BKE_brush_curve_strength_clamped(struct Brush *br, float p, const float len);
-float BKE_brush_curve_strength(struct Brush *br, float p, const float len);
+float BKE_brush_curve_strength(const struct Brush *br, float p, const float len);
 
 /* sampling */
 float BKE_brush_sample_tex_3D(

source/blender/blenkernel/BKE_paint.h

@@ -231,7 +231,7 @@ typedef struct SculptSession {
 			/* Keep track of how much each vertex has been painted (non-airbrush only). */
 			float *alpha_weight;
 
-			/* Needed to continuously re-apply over the same weights (VP_SPRAY disabled).
+			/* Needed to continuously re-apply over the same weights (VP_FLAG_SPRAY disabled).
 			 * Lazy initialize as needed (flag is set to 1 to tag it as uninitialized). */
 			struct MDeformVert *dvert_prev;
 		} wpaint;

source/blender/blenkernel/intern/brush.c

@@ -966,7 +966,7 @@ void BKE_brush_randomize_texture_coords(UnifiedPaintSettings *ups, bool mask)
 }
 
 /* Uses the brush curve control to find a strength value */
-float BKE_brush_curve_strength(Brush *br, float p, const float len)
+float BKE_brush_curve_strength(const Brush *br, float p, const float len)
 {
 	float strength;