Cleanup: Add comments for Brush.curve_preset and corresponding enum

Pull Request: https://projects.blender.org/blender/blender/pulls/146200

source/blender/makesdna/DNA_brush_enums.h

@@ -173,16 +173,26 @@ typedef enum eGP_BrushMode {
   GP_BRUSH_MODE_VERTEXCOLOR = 2,
 } eGP_BrushMode;
 
+/* Brush.curve_preset */
 typedef enum eBrushCurvePreset {
   BRUSH_CURVE_CUSTOM = 0,
+  /** Corresponds to CURVE_PRESET_SMOOTH */
   BRUSH_CURVE_SMOOTH = 1,
+  /** Corresponds to CURVE_PRESET_ROUND */
   BRUSH_CURVE_SPHERE = 2,
+  /** Corresponds to CURVE_PRESET_ROOT */
   BRUSH_CURVE_ROOT = 3,
+  /** Corresponds to CURVE_PRESET_SHARP */
   BRUSH_CURVE_SHARP = 4,
+  /** Corresponds to CURVE_PRESET_LINE */
   BRUSH_CURVE_LIN = 5,
+  /** No corresponding CurveMapping.preset */
   BRUSH_CURVE_POW4 = 6,
+  /** No corresponding CurveMapping.preset */
   BRUSH_CURVE_INVSQUARE = 7,
+  /** Corresponds to CURVE_PRESET_MAX */
   BRUSH_CURVE_CONSTANT = 8,
+  /** No corresponding CurveMapping.preset */
   BRUSH_CURVE_SMOOTHER = 9,
 } eBrushCurvePreset;
 

source/blender/makesdna/DNA_brush_types.h

@@ -330,6 +330,11 @@ typedef struct Brush {
 
   float texture_sample_bias;
 
+  /**
+   * This preset is used to specify an exact function used for the distance falloff instead
+   * of doing a Bezier spline evaluation via CurveMapping for performance reasons.
+   * \see #eBrushCurvePreset and #eCurveMappingPreset
+   */
   int curve_distance_falloff_preset;
 
   /* Maximum distance to search fake neighbors from a vertex. */