Clamp background tiles when possible

third_party/WebKit/Source/platform/graphics/Image.cpp

 /*
  * Copyright (C) 2006 Samuel Weinig (sam.weinig@gmail.com)
  * Copyright (C) 2004, 2005, 2006 Apple Computer, Inc.  All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
@@ skipping 207 matching lines @@
   }
 
   startAnimation();
 }
 
 namespace {
 
 sk_sp<SkShader> createPatternShader(const SkImage* image,
                                     const SkMatrix& shaderMatrix,
                                     const SkPaint& paint,
-                                    const FloatSize& spacing) {
+                                    const FloatSize& spacing,
+                                    SkShader::TileMode tmx,
+                                    SkShader::TileMode tmy) {
   if (spacing.isZero())
-    return image->makeShader(SkShader::kRepeat_TileMode,
-                             SkShader::kRepeat_TileMode, &shaderMatrix);
+    return image->makeShader(tmx, tmy, &shaderMatrix);
 
   // Arbitrary tiling is currently only supported for SkPictureShader, so we use
   // that instead of a plain bitmap shader to implement spacing.
   const SkRect tileRect = SkRect::MakeWH(image->width() + spacing.width(),
                                          image->height() + spacing.height());
 
   SkPictureRecorder recorder;
   SkCanvas* canvas = recorder.beginRecording(tileRect);
   canvas->drawImage(image, 0, 0, &paint);
 
-  return SkShader::MakePictureShader(
-      recorder.finishRecordingAsPicture(), SkShader::kRepeat_TileMode,
-      SkShader::kRepeat_TileMode, &shaderMatrix, nullptr);
+  return SkShader::MakePictureShader(recorder.finishRecordingAsPicture(), tmx,
+                                     tmy, &shaderMatrix, nullptr);
+}
+
+SkShader::TileMode computeTileMode(float destOffset,

[fs, 2016/12/19 16:49:22]

Maybe structure this as an interval containment check instead. Same but
different, just putting the idea on the table...

(i.e: computeTileMode(destRect.x(), destRect.maxX(), ...) et.c)

[f(malita), 2016/12/19 17:34:56]

Done.

+                                   float destSize,
+                                   float tileOffset,
+                                   float tileSize) {
+  return destOffset >= tileOffset &&
+                 destOffset + destSize <= tileOffset + tileSize
+             ? SkShader::kClamp_TileMode
+             : SkShader::kRepeat_TileMode;
 }
 
 }  // anonymous namespace
 
 void Image::drawPattern(GraphicsContext& context,
                         const FloatRect& floatSrcRect,
                         const FloatSize& scale,
                         const FloatPoint& phase,
                         SkBlendMode compositeOp,
                         const FloatRect& destRect,
@@ skipping 24 matching lines @@
   // set to the pattern's transform, which just includes scale.
   localMatrix.preScale(scale.width(), scale.height());
 
   // Fetch this now as subsetting may swap the image.
   auto imageID = image->uniqueID();
 
   image = image->makeSubset(enclosingIntRect(normSrcRect));
   if (!image)
     return;
 
+  const FloatSize tileSize(
+      image->width() * scale.width() + repeatSpacing.width(),
+      image->height() * scale.height() + repeatSpacing.height());
+  const auto tmx = computeTileMode(destRect.x(), destRect.width(), adjustedX,
+                                   tileSize.width());
+  const auto tmy = computeTileMode(destRect.y(), destRect.height(), adjustedY,
+                                   tileSize.height());
+
   {
     SkPaint paint = context.fillPaint();
     paint.setColor(SK_ColorBLACK);
     paint.setBlendMode(compositeOp);
     paint.setFilterQuality(
         context.computeFilterQuality(this, destRect, normSrcRect));
     paint.setAntiAlias(context.shouldAntialias());
-    paint.setShader(createPatternShader(
-        image.get(), localMatrix, paint,
-        FloatSize(repeatSpacing.width() / scale.width(),
-                  repeatSpacing.height() / scale.height())));
+    paint.setShader(
+        createPatternShader(image.get(), localMatrix, paint,
+                            FloatSize(repeatSpacing.width() / scale.width(),
+                                      repeatSpacing.height() / scale.height()),
+                            tmx, tmy));
     context.drawRect(destRect, paint);
   }
 
   if (currentFrameIsLazyDecoded())
     PlatformInstrumentation::didDrawLazyPixelRef(imageID);
 }
 
 PassRefPtr<Image> Image::imageForDefaultFrame() {
   RefPtr<Image> image(this);
 
@@ skipping 54 matching lines @@
   FloatRect subset = dest;
   subset.setX((dest.x() - tile.x()) / scale.width());
   subset.setY((dest.y() - tile.y()) / scale.height());
   subset.setWidth(dest.width() / scale.width());
   subset.setHeight(dest.height() / scale.height());
 
   return subset;
 }
 
 }  // namespace blink