Fix brush tip delta orientation with anchored strokes

When using anchored stroke, the stroke operator was modifying the
coordinates on the "mouse" rna property by setting them to the original
position. Because of this, all the sculpt delta calculation was failing
and the delta for these brushes was set randomly (with a 0 vector) at
the beginning of the stroke.
There is now an extra property that uses the unmodified coordinates of
the mouse to calculate the delta. Now delta orientation works as expected
in all brushes and features that require brush tip orientation.

Reviewed By: sergey

Differential Revision: https://developer.blender.org/D9183

source/blender/editors/sculpt_paint/paint_stroke.c

@@ -621,7 +621,10 @@ static void paint_brush_stroke_add_step(bContext *C,
     RNA_collection_add(op->ptr, "stroke", &itemptr);
     RNA_float_set(&itemptr, "size", ups->pixel_radius);
     RNA_float_set_array(&itemptr, "location", location);
+    /* Mouse coordinates modified by the stroke type options. */
     RNA_float_set_array(&itemptr, "mouse", mouse_out);
+    /* Original mouse coordinates. */
+    RNA_float_set_array(&itemptr, "mouse_event", mouse_in);
     RNA_boolean_set(&itemptr, "pen_flip", stroke->pen_flip);
     RNA_float_set(&itemptr, "pressure", pressure);
     RNA_float_set(&itemptr, "x_tilt", stroke->x_tilt);

source/blender/editors/sculpt_paint/sculpt.c

@@ -6607,6 +6607,7 @@ static void sculpt_update_cache_invariants(
   }
 
   copy_v2_v2(cache->mouse, cache->initial_mouse);
+  copy_v2_v2(cache->mouse_event, cache->initial_mouse);
   copy_v2_v2(ups->tex_mouse, cache->initial_mouse);
 
   /* Truly temporary data that isn't stored in properties. */
@@ -6734,8 +6735,8 @@ static void sculpt_update_brush_delta(UnifiedPaintSettings *ups, Object *ob, Bru
   SculptSession *ss = ob->sculpt;
   StrokeCache *cache = ss->cache;
   const float mouse[2] = {
-      cache->mouse[0],
-      cache->mouse[1],
+      cache->mouse_event[0],
+      cache->mouse_event[1],
   };
   int tool = brush->sculpt_tool;
 
@@ -6946,6 +6947,7 @@ static void sculpt_update_cache_variants(bContext *C, Sculpt *sd, Object *ob, Po
 
   cache->pen_flip = RNA_boolean_get(ptr, "pen_flip");
   RNA_float_get_array(ptr, "mouse", cache->mouse);
+  RNA_float_get_array(ptr, "mouse_event", cache->mouse_event);
 
   /* XXX: Use pressure value from first brush step for brushes which don't support strokes (grab,
    * thumb). They depends on initial state and brush coord/pressure/etc.

source/blender/editors/sculpt_paint/sculpt_intern.h

@@ -868,12 +868,17 @@ typedef struct StrokeCache {
   bool pen_flip;
   bool invert;
   float pressure;
-  float mouse[2];
   float bstrength;
   float normal_weight; /* from brush (with optional override) */
   float x_tilt;
   float y_tilt;
 
+  /* Position of the mouse corresponding to the stroke location, modified by the paint_stroke
+   * operator acording to the stroke type. */
+  float mouse[2];
+  /* Position of the mouse event in screen space, not modified by the stroke type. */
+  float mouse_event[2];
+
   float (*prev_colors)[4];
 
   /* The rest is temporary storage that isn't saved as a property */

source/blender/makesrna/intern/rna_brush.c

@@ -3426,6 +3426,11 @@ static void rna_def_operator_stroke_element(BlenderRNA *brna)
   RNA_def_property_array(prop, 2);
   RNA_def_property_ui_text(prop, "Mouse", "");
 
+  prop = RNA_def_property(srna, "mouse_event", PROP_FLOAT, PROP_XYZ);
+  RNA_def_property_flag(prop, PROP_IDPROPERTY);
+  RNA_def_property_array(prop, 2);
+  RNA_def_property_ui_text(prop, "Mouse Event", "");
+
   prop = RNA_def_property(srna, "pressure", PROP_FLOAT, PROP_FACTOR);
   RNA_def_property_flag(prop, PROP_IDPROPERTY);
   RNA_def_property_range(prop, 0.0f, 1.0f);