Better comments in SkXfermodeInterpretation

src/core/SkXfermodeInterpretation.h

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkXfermodeInterpretation_DEFINED
 #define SkXfermodeInterpretation_DEFINED
 
 class SkPaint;
 
-/** By analyzing the paint, we may decide we can take special
-    action. This enum lists our possible actions. */
+/**
+ *  By analyzing the paint, we may decide we can take special
+ *  action. This enum lists our possible actions.
+ */
 enum SkXfermodeInterpretation {
-    kNormal_SkXfermodeInterpretation,      // draw normally
-    kSrcOver_SkXfermodeInterpretation,     // draw as if in srcover mode
-    kSkipDrawing_SkXfermodeInterpretation  // draw nothing
+    kNormal_SkXfermodeInterpretation,      //< draw normally
+    kSrcOver_SkXfermodeInterpretation,     //< draw as if in srcover mode
+    kSkipDrawing_SkXfermodeInterpretation  //< draw nothing
 };
+
+/**
+ *  Given a paint, determine whether the paint's transfer mode can be
+ *  replaced with kSrcOver_Mode or not drawn at all.  This is used by
+ *  SkBlitter and SkPDFDevice.
+ */
 SkXfermodeInterpretation SkInterpretXfermode(const SkPaint&, bool dstIsOpaque);
 
 #endif  // SkXfermodeInterpretation_DEFINED