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.

2 files changed, 41 insertions, 2 deletions

diff --git a/source/blender/blenkernel/BKE_brush.h b/source/blender/blenkernel/BKE_brush.h
index 4d728002c87..8f069841fbc 100644
--- a/source/blender/blenkernel/BKE_brush.h
+++ b/source/blender/blenkernel/BKE_brush.h
@@ -18,7 +18,9 @@ extern "C" {
 struct Brush;
 struct ImBuf;
 struct ImagePool;
+struct Object;
 struct Main;
+struct MTex;
 struct Scene;
 struct ToolSettings;
 struct UnifiedPaintSettings;
@@ -109,6 +111,7 @@ float BKE_brush_curve_strength(const struct Brush *br, float p, float len);
  */
 float BKE_brush_sample_tex_3d(const struct Scene *scene,
                               const struct Brush *br,
+                              const struct MTex *mtex,
                               const float point[3],
                               float rgba[4],
                               int thread,
@@ -120,6 +123,24 @@ float BKE_brush_sample_masktex(const struct Scene *scene,
                                struct ImagePool *pool);
 
 /**
+ * Get the mask texture for this given object mode.
+ *
+ * This is preferred above using mtex/mask_mtex attributes directly as due to legacy these
+ * attributes got switched in sculpt mode. 
+ */
+const struct MTex *BKE_brush_mask_texture_get(const struct Brush *brush,
+                                              const eObjectMode object_mode);
+
+/**
+ * Get the color texture for this given object mode.
+ *
+ * This is preferred above using mtex/mask_mtex attributes directly as due to legacy these
+ * attributes got switched in sculpt mode.
+ */
+const struct MTex *BKE_brush_color_texture_get(const struct Brush *brush,
+                                               const eObjectMode object_mode);
+
+/**
  * Radial control.
  */
 struct ImBuf *BKE_brush_gen_radial_control_imbuf(struct Brush *br,
diff --git a/source/blender/blenkernel/intern/brush.cc b/source/blender/blenkernel/intern/brush.cc
index 20d86ea5a2d..6f1435e90b8 100644
--- a/source/blender/blenkernel/intern/brush.cc
+++ b/source/blender/blenkernel/intern/brush.cc
@@ -1974,19 +1974,37 @@ void BKE_brush_curve_preset(Brush *b, eCurveMappingPreset preset)
   BKE_curvemapping_changed(cumap, false);
 }
 
+const struct MTex *BKE_brush_mask_texture_get(const struct Brush *brush,
+                                              const eObjectMode object_mode)
+{
+  if (object_mode == OB_MODE_SCULPT) {
+    return &brush->mtex;
+  }
+  return &brush->mask_mtex;
+}
+
+const struct MTex *BKE_brush_color_texture_get(const struct Brush *brush,
+                                               const eObjectMode object_mode)
+{
+  if (object_mode == OB_MODE_SCULPT) {
+    return &brush->mask_mtex;
+  }
+  return &brush->mtex;
+}
+
 float BKE_brush_sample_tex_3d(const Scene *scene,
                               const Brush *br,
+                              const MTex *mtex,
                               const float point[3],
                               float rgba[4],
                               const int thread,
                               struct ImagePool *pool)
 {
   UnifiedPaintSettings *ups = &scene->toolsettings->unified_paint_settings;
-  const MTex *mtex = &br->mtex;
   float intensity = 1.0;
   bool hasrgb = false;
 
-  if (!mtex->tex) {
+  if (mtex == nullptr || mtex->tex == nullptr) {
     intensity = 1;
   }
   else if (mtex->brush_map_mode == MTEX_MAP_MODE_3D) {