First blitter for linear pipeline.

src/core/SkLinearBitmapPipeline.cpp

Index: src/core/SkLinearBitmapPipeline.cpp
diff --git a/src/core/SkLinearBitmapPipeline.cpp b/src/core/SkLinearBitmapPipeline.cpp
index 539547af9a903288f63a772e9a7be08b9666a614..77e034c9da4f1025a9e6c3193e095e442015967d 100644
--- a/src/core/SkLinearBitmapPipeline.cpp
+++ b/src/core/SkLinearBitmapPipeline.cpp
@@ -776,8 +776,33 @@ SkLinearBitmapPipeline::SkLinearBitmapPipeline(
     fLastStage        = blenderStage;
 }
 
+SkLinearBitmapPipeline::SkLinearBitmapPipeline(
+    const SkLinearBitmapPipeline& pipeline,
+    SkXfermode::Mode mode,
+    const SkPixmap& srcPixmap,
+    const SkImageInfo& dstInfo)
+{
+    SkASSERT(mode == SkXfermode::kSrc_Mode);
+    SkASSERT(srcPixmap.info().colorType() == dstInfo.colorType()
+             && srcPixmap.info().colorType() == kRGBA_8888_SkColorType);
+
+    fSampleStage.initSink<RGBA8888UnitRepeat>(srcPixmap.writable_addr32(0, 0), srcPixmap.width());
+    auto sampleStage = fSampleStage.get();
+    auto tilerStage = pipeline.fTileStage.cloneStageTo(sampleStage, &fTileStage);
+    tilerStage = (tilerStage != nullptr) ? tilerStage : sampleStage;
+    auto matrixStage = pipeline.fMatrixStage.cloneStageTo(tilerStage, &fMatrixStage);
+    matrixStage = (matrixStage != nullptr) ? matrixStage : tilerStage;
+    fFirstStage = matrixStage;
+    fLastStage = fSampleStage.getInterface<DestinationInterface, RGBA8888UnitRepeat>();
+}

[mtklein, 2016/04/11 16:43:25]

It is weird that we've constructed an object here where it's sensible to call
blitSpan() but not shadeSpan4f().

[herb_g, 2016/04/12 20:03:49]

I think that shadeSpan4f will go away as we restructure higher levels of the
code.

+
 void SkLinearBitmapPipeline::shadeSpan4f(int x, int y, SkPM4f* dst, int count) {
     SkASSERT(count > 0);
+    this->blitSpan(x, y, dst, count);
+}
+
+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