Add point spans, but fall back for all cases.

src/core/SkLinearBitmapPipeline.h

 /*
  * Copyright 2016 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkLinearBitmapPipeline_DEFINED
 #define SkLinearBitmapPipeline_DEFINED
 
 
 #include "SkColor.h"
 #include "SkImageInfo.h"
 #include "SkMatrix.h"
 #include "SkNx.h"
 #include "SkShader.h"
 
 using Sk4fArg = const Sk4f&;
 
 class PointProcessorInterface {
 public:
     virtual ~PointProcessorInterface() { }
     virtual void pointListFew(int n, Sk4fArg xs, Sk4fArg ys) = 0;
     virtual void pointList4(Sk4fArg xs, Sk4fArg ys) = 0;
+
+    // The pointSpan method efficiently process horizontal spans of pixels.
+    // * start - the point where to start the span.
+    // * length - the number of pixels to traverse in source space.
+    // * count - the number of pixels to produce in destination space.
+    // Both start and length are mapped through the inversion matrix to produce values in source
+    // space. After the matrix operation, the tilers may break the spans up into smaller spans.
+    // The tilers can produce spans that seem nonsensical.
+    // * The clamp tiler can create spans with length of 0. This indicates to copy an edge pixel out
+    //   to the edge of the destination scan.
+    // * The mirror tiler can produce spans with negative length. This indicates that the source
+    //   should be traversed in the opposite direction to the destination pixels.
+    virtual void pointSpan(SkPoint start, SkScalar length, int count) = 0;
 };
 
 class BilerpProcessorInterface : public PointProcessorInterface {
 public:
     // The x's and y's are setup in the following order:
     // +--------+--------+
     // |        |        |
     // |  px00  |  px10  |
     // |    0   |    1   |
     // +--------+--------+
@@ skipping 60 matching lines @@
     PointProcessorInterface* fFirstStage;
     MatrixStage fMatrixStage;
     FilterStage fFilterStage;
     TileStage   fTileXOrBothStage;
     TileStage   fTileYStage;
     SampleStage fSampleStage;
     PixelStage  fPixelStage;
 };
 
 #endif  // SkLinearBitmapPipeline_DEFINED