add isClipEmpty() -- encourage clients to call this rather than checking clipFoo() results

include/core/SkCanvas.h

 /*
  * Copyright 2006 The Android Open Source Project
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkCanvas_DEFINED
 #define SkCanvas_DEFINED
 
@@ skipping 954 matching lines @@
         exists, its refcnt is decrement. If the new filter is not null, its
         refcnt is incremented. The filter is saved/restored, just like the
         matrix and clip.
         @param filter the new filter (or NULL)
         @return the new filter
     */
     virtual SkDrawFilter* setDrawFilter(SkDrawFilter* filter);
 
     //////////////////////////////////////////////////////////////////////////
 
+    /**
+     *  Return true if the current clip is empty (i.e. nothing will draw).
+     *  Note: this is not always a free call, so it should not be used
+     *  more often than necessary. However, once the canvas has computed this
+     *  result, subsequent calls will be cheap (until the clip state changes,
+     *  which can happen on any clip..() or restore() call.
+     */
+    bool isClipEmpty() const;
+
     /** Return the current matrix on the canvas.
         This does not account for the translate in any of the devices.
         @return The current matrix on the canvas.
     */
     const SkMatrix& getTotalMatrix() const;
 
     enum ClipType {
         kEmpty_ClipType = 0,
         kRect_ClipType,
         kComplex_ClipType
@@ skipping 306 matching lines @@
     bool asROBitmap(SkBitmap*) const;
 
 private:
     SkBitmap    fBitmap;    // used if peekPixels() fails
     const void* fAddr;      // NULL on failure
     SkImageInfo fInfo;
     size_t      fRowBytes;
 };
 
 #endif