refactor SkRasterPipelineBlitter

This refactors the factories so that the create-from-paint factory is a
front-patch to the create-from-shader-pipeline factory.  Feature-wise,
we make the pre-baked shader pipeline responsible for modulating by
paint alpha; the factory only adds when creating from the paint.

We can fold the alpha into the colors in drawVertices, which makes it
run a bit faster, dropping the need for a scale_1_float runtime stage.
This causes a few invisible diffs on the "vertices" GM, but everything
else draws the same.

Change-Id: I3eeacc9aafbce2023ab18991bbb68c35645e9387
Reviewed-on: https://skia-review.googlesource.com/17395
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Mike Klein <mtklein@chromium.org>

1 files changed, 15 insertions, 5 deletions

diff --git a/src/core/SkDraw_vertices.cpp b/src/core/SkDraw_vertices.cpp
index 9735fa8a25..ceeb3c2ddc 100644
--- a/src/core/SkDraw_vertices.cpp
+++ b/src/core/SkDraw_vertices.cpp
@@ -257,9 +257,9 @@ void SkTriColorShader::TriColorShaderContext::shadeSpan4f(int x, int y, SkPM4f d
 #ifndef SK_IGNORE_TO_STRING
 void SkTriColorShader::toString(SkString* str) const {
     str->append("SkTriColorShader: (");
-    
+
     this->INHERITED::toString(str);
-    
+
     str->append(")");
 }
 #endif
@@ -472,6 +472,17 @@ void SkDraw::drawVertices(SkVertices::VertexMode vmode, int count,
         //
         SkPM4f* dstColors = convert_colors(colors, count, fDst.colorSpace(), &alloc);
 
+        bool is_opaque;
+        if (paint.getAlpha() == 0xff) {
+            is_opaque = compute_is_opaque(colors, count);
+        } else {
+            is_opaque = false;
+            Sk4f alpha = paint.getAlpha() * (1/255.0f);
+            for (int i = 0; i < count; i++) {
+                (dstColors[i].to4f() * alpha).store(dstColors + i);
+            }
+        }
+
         shaderPipeline.append(SkRasterPipeline::matrix_4x3, &matrix43);
         // In theory we should never need to clamp. However, either due to imprecision in our
         // matrix43, or the scan converter passing us pixel centers that in fact are not within
@@ -480,9 +491,8 @@ void SkDraw::drawVertices(SkVertices::VertexMode vmode, int count,
         shaderPipeline.append(SkRasterPipeline::clamp_0);
         shaderPipeline.append(SkRasterPipeline::clamp_a);
 
-        bool is_opaque = compute_is_opaque(colors, count),
-             wants_dither = paint.isDither();
-        auto blitter = SkCreateRasterPipelineBlitter(fDst, paint, *fMatrix, shaderPipeline,
+        bool wants_dither = paint.isDither();
+        auto blitter = SkCreateRasterPipelineBlitter(fDst, paint, shaderPipeline,
                                                      is_opaque, wants_dither, &alloc);
         SkASSERT(!blitter->isNullBlitter());