Brush: Wrap mtex/mask_tex around functions.

`Brush` has two attributes for holding texture information (`MTex`).
One for color textures (`mtex`) and one for mask textures (`mask_mtex`).

Unfortunately sculpt mode due to reasons used `mtex` to store mask textures.
Changes like brush asset/paint mode require modes/tools to read the mask/color texture from
one place.

To start sanatizing this we isolate the attributes in functions.
`BKE_brush_color_texture_get` and `BKE_brush_mask_texture_get`. All object
paint modes should use these functions.

1 files changed, 4 insertions, 3 deletions

diff --git a/source/blender/editors/sculpt_paint/sculpt_expand.c b/source/blender/editors/sculpt_paint/sculpt_expand.c
index 655b03bbb36..3133bb2007e 100644
--- a/source/blender/editors/sculpt_paint/sculpt_expand.c
+++ b/source/blender/editors/sculpt_paint/sculpt_expand.c
@@ -167,15 +167,16 @@ static float sculpt_expand_falloff_value_vertex_get(SculptSession *ss,
   if (expand_cache->texture_distortion_strength == 0.0f) {
     return expand_cache->vert_falloff[v_i];
   }
-
-  if (!expand_cache->brush->mtex.tex) {
+  const Brush *brush = expand_cache->brush;
+  const MTex *mtex = BKE_brush_mask_texture_get(brush, OB_MODE_SCULPT);
+  if (!mtex->tex) {
     return expand_cache->vert_falloff[v_i];
   }
 
   float rgba[4];
   const float *vertex_co = SCULPT_vertex_co_get(ss, v);
   const float avg = BKE_brush_sample_tex_3d(
-      expand_cache->scene, expand_cache->brush, vertex_co, rgba, 0, ss->tex_pool);
+      expand_cache->scene, brush, mtex, vertex_co, rgba, 0, ss->tex_pool);
 
   const float distortion = (avg - 0.5f) * expand_cache->texture_distortion_strength *
                            expand_cache->max_vert_falloff;