SkRasterPipeline preliminaries

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, const void* body_ctx,
+                              SkRasterPipeline::Fn tail, const void* tail_ctx) {
+    // We can't add more stages after being rewired to run().
+    SkASSERT(!fReadyToRun);
+
+    // For now, just stash the stage's function in its own fNext slot.
+    // We'll rewire our stages before running the pipeline so fNext makes sense.
+    fBody.push_back({ body, const_cast<void*>(body_ctx) });
+    fTail.push_back({ tail, const_cast<void*>(tail_ctx) });
+}
+
+void SkRasterPipeline::run(size_t n) {
+    if (fBody.empty() || fTail.empty()) {
+        return;
+    }
+
+    if (!fReadyToRun) {
+        auto rewire = [](Stages* stages) {
+            SkASSERT(!stages->empty());
+
+            // Rotate the fNext pointers so they point to the next function to
+            // call, not function we're currently calling as set by append().
+            auto start = stages->front().fNext;
+            for (int i = 0; i < stages->count() - 1; i++) {
+                (*stages)[i].fNext = (*stages)[i+1].fNext;
+            }
+            stages->back().fNext = start;  // This is a pretty handy place to stash this.
+        };
+        rewire(&fBody);
+        rewire(&fTail);
+        fReadyToRun = true;
+    }
+
+    // It's fastest to start uninitialized if the compilers all let us.  If not, next fastest is 0.
+    Sk4f v;
+
+    auto start_body = fBody.back().fNext,  // See rewire().
+         start_tail = fTail.back().fNext;
+
+    auto body = fBody.begin(),
+         tail = fTail.begin();
+
+    size_t x = 0;
+    while (n >= 4) {
+        start_body(body, x, v,v,v,v, v,v,v,v);
+        x += 4;
+        n -= 4;
+    }
+    while (n > 0) {
+        start_tail(tail, x, v,v,v,v, v,v,v,v);
+        x += 1;
+        n -= 1;
+    }
+}