Simplify mask/clip intersection, making sure to explicitly check for an empty mask.

src/core/SkDraw.cpp

 /*
  * 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.
  */
 #define __STDC_LIMIT_MACROS
 
 #include "SkDraw.h"
 #include "SkBlitter.h"
@@ skipping 1470 matching lines @@
             SkRegion::Cliperator clipper(*fClip, mask.fBounds);
 
             if (!clipper.done() && this->getImageData(glyph, &mask)) {
                 const SkIRect& cr = clipper.rect();
                 do {
                     this->blitMask(mask, cr);
                     clipper.next();
                 } while (!clipper.done());
             }
         } else {
-            SkIRect  storage;
-            SkIRect* bounds = &mask.fBounds;
-
-            // this extra test is worth it, assuming that most of the time it succeeds
-            // since we can avoid writing to storage
-            if (!fClipBounds.containsNoEmptyCheck(mask.fBounds)) {
-                if (!storage.intersectNoEmptyCheck(mask.fBounds, fClipBounds))
-                    return;
-                bounds = &storage;
+            SkIRect storage;
+            if (mask.fBounds.isEmpty() ||

[reed1, 2016/06/17 10:39:42]

I wonder 

1. if it would be clearer to put this empty check after line 1478, since we care
about empty/inverted in both cases.
2. we add a comment explaining why we need to check, even though the logic on
lines 1474-5 would seem to mean we could never be empty/inverted.

+                    !storage.intersectNoEmptyCheck(mask.fBounds, fClipBounds)) {
+                return;
             }
 
             if (this->getImageData(glyph, &mask)) {
-                this->blitMask(mask, *bounds);
+                this->blitMask(mask, storage);
             }
         }
     }
 
 private:
     static bool UsingRegionToDraw(const SkRasterClip* rClip) {
         return rClip->isBW() && !rClip->isRect();
     }
 
     static SkIRect PickClipBounds(const SkDraw& draw) {
@@ skipping 562 matching lines @@
         mask->fImage = SkMask::AllocImage(size);
         memset(mask->fImage, 0, mask->computeImageSize());
     }
 
     if (SkMask::kJustComputeBounds_CreateMode != mode) {
         draw_into_mask(*mask, devPath, style);
     }
 
     return true;
 }