Add SkGammaColorFilter

gm/gammacolorfilter.cpp

Index: gm/gammacolorfilter.cpp
diff --git a/gm/gammacolorfilter.cpp b/gm/gammacolorfilter.cpp
new file mode 100644
index 0000000000000000000000000000000000000000..ecb2daa2147a50f289f53bdad896fe343e7c3f66
--- /dev/null
+++ b/gm/gammacolorfilter.cpp
@@ -0,0 +1,101 @@
+/*
+ * 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 "gm.h"
+#include "SkGammaColorFilter.h"
+#include "SkImage.h"
+
+// Fill a width x height block with a horizontal ramp from 0 to 255
+static void draw_grey_ramp(SkCanvas* canvas, int width, int height, int numSteps) {
+    int greyPerStep = SkScalarRoundToInt(255.0f / numSteps);
+    int widthPerStep = SkScalarRoundToInt(width / SkIntToScalar(numSteps));
+
+    SkIRect rect = SkIRect::MakeWH(widthPerStep, height);
+
+    SkPaint paint;
+    int grey = 0;
+    int x = 0;
+    for (int i = 0; i < numSteps-1; ++i) {
+        paint.setColor(SkColorSetARGB(255, grey, grey, grey));
+
+        rect.offsetTo(x, 0);
+        canvas->drawRect(SkRect::Make(rect), paint);
+
+        x += widthPerStep;
+        grey += greyPerStep;
+    }
+
+    paint.setColor(SK_ColorWHITE);
+    rect.setLTRB(x, 0, width, height);
+    canvas->drawRect(SkRect::Make(rect), paint);
+}
+
+static sk_sp<SkImage> create_grey_ramp(int width, int height, int numSteps) {
+    SkBitmap bm;
+    bm.allocN32Pixels(width, height);
+    SkCanvas canvas(bm);
+    canvas.clear(0x0);
+
+    draw_grey_ramp(&canvas, width, height, numSteps);
+
+    return SkImage::MakeFromBitmap(bm);
+}
+
+namespace skiagm {
+
+class GammaColorFilterGM : public GM {
+public:
+    GammaColorFilterGM() {
+        this->setBGColor(SK_ColorBLACK);
+    }
+
+protected:
+
+    SkString onShortName() override {
+        return SkString("gammacolorfilter");
+    }
+
+    SkISize onISize() override {
+        return SkISize::Make(4 * kCellWidth, kCellHeight);
+    }
+
+    void onDraw(SkCanvas* canvas) override {
+        GrDrawContext* drawContext = canvas->internal_private_accessTopLayerDrawContext();
+        if (!drawContext) {
+            skiagm::GM::DrawGpuOnlyMessage(canvas);
+            return;
+        }
+
+        sk_sp<SkImage> image(create_grey_ramp(kCellWidth, kCellHeight/2, kNumGreySteps));
+
+        // Leftmost is a non-gamma pair
+        draw_grey_ramp(canvas, kCellWidth, kCellHeight/2, kNumGreySteps);
+        canvas->drawImage(image, 0, kCellHeight/2);
+        canvas->translate(SkIntToScalar(image->width()), 0);
+
+        for (auto gamma : { 1.0f, 1.0f / 1.8f, 1.0f / 2.2f }) {
+            SkPaint paint;
+            paint.setColorFilter(SkGammaColorFilter::Make(gamma));
+
+            draw_grey_ramp(canvas, kCellWidth, kCellHeight/2, kNumGreySteps);
+            canvas->drawImage(image, 0, kCellHeight/2, &paint);
+            canvas->translate(SkIntToScalar(image->width()), 0);
+        }
+    }
+
+private:
+    static const int kCellWidth = 64;
+    static const int kCellHeight = 64;
+    static const int kNumGreySteps = 16;
+
+    typedef GM INHERITED;
+};
+
+//////////////////////////////////////////////////////////////////////////////
+
+DEF_GM(return new GammaColorFilterGM;)
+}