Add guards for edge cases.

src/core/SkLinearBitmapPipeline.cpp

 /*
  * Copyright 2016 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkLinearBitmapPipeline.h"
 
 #include "SkPM4f.h"
@@ skipping 566 matching lines @@
         Sk4i iXs = SkNx_cast<int>(xs);
         Sk4i iYs = SkNx_cast<int>(ys);
         *fDest++ = *this->pixelAddress(iXs[0], iYs[0]);
         *fDest++ = *this->pixelAddress(iXs[1], iYs[1]);
         *fDest++ = *this->pixelAddress(iXs[2], iYs[2]);
         *fDest++ = *this->pixelAddress(iXs[3], iYs[3]);
     }
 
     void pointSpan(Span span) override {
         SkASSERT(fDest + span.count() <= fEnd);
-        int32_t x = (int32_t)span.startX();
-        int32_t y = (int32_t)span.startY();
-        const uint32_t* src = this->pixelAddress(x, y);
-        memmove(fDest, src, span.count() * sizeof(uint32_t));
-        fDest += span.count();
+        if (span.length() != 0.0f) {
+            int32_t x = (int32_t)span.startX();

[Brian Osman, 2016/04/25 20:00:18]

Should these be using SkScalarFloorToInt, just to be more explicit about the
conversion that's happening?

[herb_g, 2016/04/25 20:36:36]

At this point, I know that startX > 0, so I want the much faster truncate
behavior. Changed to SkScalarTruncToInt, which I didn't know existed. Thanks.

+            int32_t y = (int32_t)span.startY();
+            const uint32_t* src = this->pixelAddress(x, y);
+            memmove(fDest, src, span.count() * sizeof(uint32_t));
+            fDest += span.count();
+        }
     }
 
     void repeatSpan(Span span, int32_t repeatCount) override {
         SkASSERT(fDest + span.count() * repeatCount <= fEnd);
 
         int32_t x = (int32_t)span.startX();
         int32_t y = (int32_t)span.startY();
         const uint32_t* src = this->pixelAddress(x, y);
         uint32_t* dest = fDest;
         while (repeatCount --> 0) {
@@ skipping 245 matching lines @@
 void SkLinearBitmapPipeline::blitSpan(int x, int y, void* dst, int count) {
     SkASSERT(count > 0);
     fLastStage->setDestination(dst, count);
 
     // The count and length arguments start out in a precise relation in order to keep the
     // math correct through the different stages. Count is the number of pixel to produce.
     // Since the code samples at pixel centers, length is the distance from the center of the
     // first pixel to the center of the last pixel. This implies that length is count-1.
     fFirstStage->pointSpan(Span{{x + 0.5f, y + 0.5f}, count - 1.0f, count});
 }