specialize drawAtlas for raster backend

2x faster than calling drawVertices as the impl.

Lots more to do in future CLs
- much of the time is spent in malloc, as we cons-up private shaders.
  we *could* create a private shader and wack its data for each draw
  (breaking the immutable contract, but that may be ok for a raster-only
  internal-use shader...)
- also spend time building the pipeline for each draw, even though
  all that has changed is a color payload (and the ctm). A custome
  stage(s) that exposed its private data could be reused with new
  data...

Bug: skia:
Change-Id: I0ff15155e37c0af7931abd34c0883701a47a048a
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/203168
Reviewed-by: Mike Klein <mtklein@google.com>
Commit-Queue: Mike Reed <reed@google.com>

bench/VertBench.cpp

@@ -139,7 +139,7 @@ protected:
         for (int i = 0; i < N; ++i) {
             fRects[i] = SkRect::MakeXYWH(rand.nextF() * (imageW - 8),
                                          rand.nextF() * (imageH - 8), 8, 8);
-            fColors[i] = rand.nextU();
+            fColors[i] = rand.nextU() | 0xFF000000;
             fXforms[i] = SkRSXform::Make(1, 0, rand.nextF() * W, rand.nextF() * H);
         }
     }
@@ -155,7 +155,7 @@ protected:
             atlas = fAtlas.get();
         }
         for (int i = 0; i < loops; i++) {
-            canvas->drawAtlas(atlas, fXforms, fRects, colors, N, SkBlendMode::kSrcOver,
+            canvas->drawAtlas(atlas, fXforms, fRects, colors, N, SkBlendMode::kModulate,
                               cullRect, paintPtr);
         }
     }

gn/core.gni

@@ -177,6 +177,7 @@ skia_core_sources = [
   "$_src/core/SkDistanceFieldGen.h",
   "$_src/core/SkDocument.cpp",
   "$_src/core/SkDraw.cpp",
+  "$_src/core/SkDraw_atlas.cpp",
   "$_src/core/SkDraw_text.cpp",
   "$_src/core/SkDraw_vertices.cpp",
   "$_src/core/SkDraw.h",

src/core/SkBitmapDevice.cpp

@@ -575,6 +575,17 @@ void SkBitmapDevice::drawDevice(SkBaseDevice* device, int x, int y, const SkPain
     }
 }
 
+void SkBitmapDevice::drawAtlas(const SkImage* atlas, const SkRSXform xform[],
+                               const SkRect tex[], const SkColor colors[], int count,
+                               SkBlendMode mode, const SkPaint& paint) {
+    // set this to true for performance comparisons with the old drawVertices way
+    if (false) {
+        this->INHERITED::drawAtlas(atlas, xform, tex, colors, count, mode, paint);
+        return;
+    }
+    BDDraw(this).drawAtlas(atlas, xform, tex, colors, count, mode, paint);
+}
+
 ///////////////////////////////////////////////////////////////////////////////
 
 namespace {

src/core/SkBitmapDevice.h

@@ -101,6 +101,8 @@ protected:
     void drawGlyphRunList(const SkGlyphRunList& glyphRunList) override;
     void drawVertices(const SkVertices*, const SkVertices::Bone bones[], int boneCount, SkBlendMode,
                       const SkPaint& paint) override;
+    void drawAtlas(const SkImage*, const SkRSXform[], const SkRect[], const SkColor[], int count,
+                   SkBlendMode, const SkPaint&) override;
     void drawDevice(SkBaseDevice*, int x, int y, const SkPaint&) override;
 
     ///////////////////////////////////////////////////////////////////////////

src/core/SkDraw.h

@@ -68,6 +68,8 @@ public:
                          const SkVertices::BoneWeights boneWeights[], SkBlendMode bmode,
                          const uint16_t indices[], int ptCount,
                          const SkPaint& paint, const SkVertices::Bone bones[], int boneCount) const;
+    void  drawAtlas(const SkImage*, const SkRSXform[], const SkRect[], const SkColor[], int count,
+                    SkBlendMode, const SkPaint&);
 
     /**
      *  Overwrite the target with the path's coverage (i.e. its mask).

src/core/SkDraw_atlas.cpp

@@ -0,0 +1,49 @@
+/*
+ * Copyright 2019 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "include/core/SkColorFilter.h"
+#include "include/core/SkRSXform.h"
+#include "src/core/SkDraw.h"
+#include "src/core/SkScan.h"
+#include "src/shaders/SkShaderBase.h"
+
+void SkDraw::drawAtlas(const SkImage* atlas, const SkRSXform xform[], const SkRect textures[],
+                       const SkColor colors[], int count, SkBlendMode bmode, const SkPaint& paint) {
+    SkDraw draw(*this);
+    SkPaint p(paint);
+
+    p.setAntiAlias(false);  // we never respect this for drawAtlas(or drawVertices)
+    p.setStyle(SkPaint::kFill_Style);
+    p.setShader(nullptr);
+    p.setMaskFilter(nullptr);
+
+    sk_sp<SkShader> atlasShader;
+    if (atlas) {
+        atlasShader = atlas->makeShader();
+    }
+
+    SkMatrix xf;
+    for (int i = 0; i < count; ++i) {
+        if (colors) {
+            if (atlasShader) {
+                p.setShader(SkShaders::Blend(bmode,
+                                             SkShaders::Color(colors[i]),
+                                             atlasShader));
+                p.setColor4f(paint.getColor4f(), nullptr);
+            } else {
+                p.setColor(colors[i]);  // modulate with paint.getAlpha()?
+            }
+        } else {
+            p.setShader(atlasShader);
+        }
+        xf.setRSXform(xform[i]);
+        xf.preTranslate(-textures[i].fLeft, -textures[i].fTop);
+        xf.postConcat(*fMatrix);
+        draw.fMatrix = &xf;
+        draw.drawRect(textures[i], p);
+    }
+}