Add SkGammaColorFilter

include/effects/SkGammaColorFilter.h

+/*
+ * Copyright 2016 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#ifndef SkGammaColorFilter_DEFINED
+#define SkGammaColorFilter_DEFINED
+
+#include "SkColorFilter.h"
+#include "SkRefCnt.h"
+
+// This colorfilter can be used to perform pixel-by-pixel conversion between linear and 
+// power-law color spaces. A gamma of 2.2 is interpreted to mean convert from sRGB to linear
+// while a gamma of 1/2.2 is interpreted to mean convert from linear to sRGB. Any other 
+// values are just directly applied (i.e., out = in^gamma)
+// 
+// More complicated color space mapping (i.e., ICC profiles) should be handled via the
+// SkColorSpace object.
+class SK_API SkGammaColorFilter : public SkColorFilter {
+public:
+    static sk_sp<SkColorFilter> Make(SkScalar gamma);
+
+#ifdef SK_SUPPORT_LEGACY_COLORFILTER_PTR
+    static SkColorFilter* Create(SkScalar gamma) { return Make(gamma).release(); }
+#endif
+
+    void filterSpan(const SkPMColor src[], int count, SkPMColor[]) const override;
+
+#if SK_SUPPORT_GPU
+    sk_sp<GrFragmentProcessor> asFragmentProcessor(GrContext*) const override;
+#endif
+
+    SK_TO_STRING_OVERRIDE()
+    SK_DECLARE_PUBLIC_FLATTENABLE_DESERIALIZATION_PROCS(SkLumaColorFilter)
+
+protected:
+    void flatten(SkWriteBuffer&) const override;
+
+private:
+    SkGammaColorFilter(SkScalar gamma);
+
+    SkScalar fGamma;
+    typedef SkColorFilter INHERITED;
+};
+
+#endif