New option for arithmetic mode

include/effects/SkValidateImageFilter.h

+/*
+ * Copyright 2014 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#ifndef SkValidateImageFilter_DEFINED

[Stephen White, 2014/03/25 17:10:14]

Bikeshed: the name doesn't really explain what it's validating.

Some ideas:

SkValidatePremulImageFilter
SkValidatePMColorImageFilter
SkForceValidPMColorImageFilter
SkForceValidPMImageFilter
SkForceValidPremulImageFilter

I think I like the last one the best, but I'd like to hear Mike's opinion too.

+#define SkValidateImageFilter_DEFINED
+
+#include "SkImageFilter.h"
+#include "SkBitmap.h"
+
+class SK_API SkValidateImageFilter : public SkImageFilter {
+public:
+    ~SkValidateImageFilter();
+
+    static SkValidateImageFilter* Create(SkImageFilter* input = NULL) {
+        return SkNEW_ARGS(SkValidateImageFilter, (input));
+    }
+
+    SK_DECLARE_PUBLIC_FLATTENABLE_DESERIALIZATION_PROCS(SkValidateImageFilter)
+
+    virtual bool onFilterImage(Proxy* proxy,
+                               const SkBitmap& src,
+                               const Context& ctx,
+                               SkBitmap* dst,
+                               SkIPoint* offset) const SK_OVERRIDE;
+
+#if SK_SUPPORT_GPU
+    virtual bool canFilterImageGPU() const SK_OVERRIDE { return true; }
+    virtual bool filterImageGPU(Proxy* proxy, const SkBitmap& src, const Context& ctx,
+                                SkBitmap* result, SkIPoint* offset) const SK_OVERRIDE;
+#endif
+
+protected:
+    explicit SkValidateImageFilter(SkReadBuffer& buffer);
+    virtual void flatten(SkWriteBuffer&) const SK_OVERRIDE;
+
+    SkValidateImageFilter(SkImageFilter* input = NULL);
+
+private:
+    typedef SkImageFilter INHERITED;
+};
+
+#endif