Add SkRasterPipeline blitter.

src/core/SkRasterPipeline.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 "SkRasterPipeline.h"
 
 SkRasterPipeline::SkRasterPipeline() {}
 
 void SkRasterPipeline::append(SkRasterPipeline::Fn body_fn, const void* body_ctx,
                               SkRasterPipeline::Fn tail_fn, const void* tail_ctx) {
     // Each stage holds its own context and the next function to call.
     // So the pipeline itself has to hold onto the first function that starts the pipeline.
     (fBody.empty() ? fBodyStart : fBody.back().fNext) = body_fn;
     (fTail.empty() ? fTailStart : fTail.back().fNext) = tail_fn;
 
     // Each last stage starts with its next function set to JustReturn as a safety net.
     // It'll be overwritten by the next call to append().
     fBody.push_back({ &JustReturn, const_cast<void*>(body_ctx) });
     fTail.push_back({ &JustReturn, const_cast<void*>(tail_ctx) });
 }
 
-void SkRasterPipeline::run(size_t n) {
+void SkRasterPipeline::extend(const SkRasterPipeline& src) {
+    SkASSERT(src.fBody.count() == src.fTail.count());
+
+    Fn body_fn = src.fBodyStart,
+       tail_fn = src.fTailStart;
+    for (int i = 0; i < src.fBody.count(); i++) {
+        this->append(body_fn, src.fBody[i].fCtx,
+                     tail_fn, src.fTail[i].fCtx);
+        body_fn = src.fBody[i].fNext;
+        tail_fn = src.fTail[i].fNext;
+    }
+}
+
+void SkRasterPipeline::run(size_t x, size_t n) {
     // It's fastest to start uninitialized if the compilers all let us.  If not, next fastest is 0.
     Sk4f v;
 
-    size_t x = 0;
     while (n >= 4) {
         fBodyStart(fBody.begin(), x, v,v,v,v, v,v,v,v);
         x += 4;
         n -= 4;
     }
     while (n > 0) {
         fTailStart(fTail.begin(), x, v,v,v,v, v,v,v,v);
         x += 1;
         n -= 1;
     }
 }
 
 void SK_VECTORCALL SkRasterPipeline::JustReturn(Stage*, size_t, Sk4f,Sk4f,Sk4f,Sk4f,
                                                                 Sk4f,Sk4f,Sk4f,Sk4f) {}