Provide a GPU implementation of SkArithmeticMode

gm/arithimagefilter.cpp

Index: gm/arithimagefilter.cpp
diff --git a/gm/blend.cpp b/gm/arithimagefilter.cpp
similarity index 55%
copy from gm/blend.cpp
copy to gm/arithimagefilter.cpp
index 452eb4945cb91f464eca7b10efa64e20b2f9770b..5ae074550b9f8687a3ffddd9a9062489a11cee2b 100644
--- a/gm/blend.cpp
+++ b/gm/arithimagefilter.cpp
@@ -1,25 +1,29 @@
 /*
- * Copyright 2012 Google Inc.
+ * Copyright 2013 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "gm.h"
-#include "SkBlendImageFilter.h"
+#include "SkArithmeticImageFilter.h"
 #include "SkBitmapSource.h"
 
+#define WIDTH 500
+#define HEIGHT 300
+#define MARGIN 12
+
 namespace skiagm {
 
-class ImageBlendGM : public GM {
+class ArithmeticImageFilterGM : public GM {
 public:
-    ImageBlendGM() : fInitialized(false) {
+    ArithmeticImageFilterGM() : fInitialized(false) {
         this->setBGColor(0xFF000000);
     }
 
 protected:
     virtual SkString onShortName() {
-        return SkString("blend");
+        return SkString("arithimagefilter");
     }
 
     void make_bitmap() {
@@ -60,14 +64,14 @@ protected:
     }
 
     virtual SkISize onISize() {
-        return make_isize(500, 100);
+        return make_isize(WIDTH, HEIGHT);
     }
 
-    void drawClippedBitmap(SkCanvas* canvas, const SkPaint& paint, int x) {
+    void drawClippedBitmap(SkCanvas* canvas, const SkBitmap& bitmap, const SkPaint& paint, SkScalar x, SkScalar y) {
         canvas->save();
-        canvas->clipRect(SkRect::MakeXYWH(SkIntToScalar(x), 0,
-            SkIntToScalar(fBitmap.width()), SkIntToScalar(fBitmap.height())));
-        canvas->drawBitmap(fBitmap, SkIntToScalar(x), 0, &paint);
+        canvas->clipRect(SkRect::MakeXYWH(x, y,
+            SkIntToScalar(bitmap.width()), SkIntToScalar(bitmap.height())));
+        canvas->drawBitmap(bitmap, x, y, &paint);
         canvas->restore();
     }
 
@@ -79,19 +83,36 @@ protected:
         }
         canvas->clear(0x00000000);
         SkPaint paint;
-        SkAutoTUnref<SkImageFilter> background(SkNEW_ARGS(SkBitmapSource, (fCheckerboard)));
-        paint.setImageFilter(SkNEW_ARGS(SkBlendImageFilter, (SkBlendImageFilter::kNormal_Mode, background)))->unref();
-        drawClippedBitmap(canvas, paint, 0);
-        paint.setImageFilter(SkNEW_ARGS(SkBlendImageFilter, (SkBlendImageFilter::kMultiply_Mode, background)))->unref();
-        drawClippedBitmap(canvas, paint, 100);
-        paint.setImageFilter(SkNEW_ARGS(SkBlendImageFilter, (SkBlendImageFilter::kScreen_Mode, background)))->unref();
-        drawClippedBitmap(canvas, paint, 200);
-        paint.setImageFilter(SkNEW_ARGS(SkBlendImageFilter, (SkBlendImageFilter::kDarken_Mode, background)))->unref();
-        drawClippedBitmap(canvas, paint, 300);
-        paint.setImageFilter(SkNEW_ARGS(SkBlendImageFilter, (SkBlendImageFilter::kLighten_Mode, background)))->unref();
-        drawClippedBitmap(canvas, paint, 400);
-    }
 
+        const SkScalar one = SK_Scalar1;
+        static const SkScalar kValues[] = {
+            0, 0, 0, 0,
+            0, 0, 0, one,
+            0, one, 0, 0,
+            0, 0, one, 0,
+            0, one, one, 0,
+            0, one, -one, 0,
+            0, one/2, one/2, 0,
+            0, one/2, one/2, one/4,
+            0, one/2, one/2, -one/4,
+            one/4, one/2, one/2, 0,
+            -one/4, one/2, one/2, 0,
+        };
+
+        int x = 0, y = 0;
+        const SkScalar* kEnd = kValues + SK_ARRAY_COUNT(kValues);
+        for (const SkScalar* k = kValues; k < kEnd; k += 4) {
+            SkAutoTUnref<SkImageFilter> background(SkNEW_ARGS(SkBitmapSource, (fCheckerboard)));
+            SkAutoTUnref<SkImageFilter> arith(SkNEW_ARGS(SkArithmeticImageFilter, (k[0], k[1], k[2], k[3], background)));
+            paint.setImageFilter(arith);
+            drawClippedBitmap(canvas, fBitmap, paint, SkIntToScalar(x), SkIntToScalar(y));
+            x += fBitmap.width() + MARGIN;
+            if (x + fBitmap.width() > WIDTH) {
+                x = 0;
+                y += fBitmap.height() + MARGIN;
+            }
+        }
+    }
 private:
     typedef GM INHERITED;
     SkBitmap fBitmap, fCheckerboard;
@@ -100,7 +121,7 @@ private:
 
 //////////////////////////////////////////////////////////////////////////////
 
-static GM* MyFactory(void*) { return new ImageBlendGM; }
+static GM* MyFactory(void*) { return new ArithmeticImageFilterGM; }
 static GMRegistry reg(MyFactory);
 
 }