1 files changed, 37 insertions, 0 deletions
diff --git a/gfx/skia/skia/include/effects/SkLumaColorFilter.h b/gfx/skia/skia/include/effects/SkLumaColorFilter.h
new file mode 100644
index 0000000000..41a9a45f3f
--- /dev/null
+++ b/gfx/skia/skia/include/effects/SkLumaColorFilter.h
@@ -0,0 +1,37 @@
+/*
+ * Copyright 2013 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#ifndef SkLumaColorFilter_DEFINED
+#define SkLumaColorFilter_DEFINED
+
+#include "include/core/SkRefCnt.h"
+#include "include/core/SkTypes.h"
+
+class SkColorFilter;
+
+/**
+ *  SkLumaColorFilter multiplies the luma of its input into the alpha channel,
+ *  and sets the red, green, and blue channels to zero.
+ *
+ *    SkLumaColorFilter(r,g,b,a) = {0,0,0, a * luma(r,g,b)}
+ *
+ *  This is similar to a luminanceToAlpha feColorMatrix,
+ *  but note how this filter folds in the previous alpha,
+ *  something an feColorMatrix cannot do.
+ *
+ *    feColorMatrix(luminanceToAlpha; r,g,b,a) = {0,0,0, luma(r,g,b)}
+ *
+ *  (Despite its name, an feColorMatrix using luminanceToAlpha does
+ *  actually compute luma, a dot-product of gamma-encoded color channels,
+ *  not luminance, a dot-product of linear color channels.  So at least
+ *  SkLumaColorFilter and feColorMatrix+luminanceToAlpha agree there.)
+ */
+struct SK_API SkLumaColorFilter {
+    static sk_sp<SkColorFilter> Make();
+};
+
+#endif