Do premul and r/b swap conversions in a custom effect
Review URL: https://codereview.appspot.com/6473060/
git-svn-id: http://skia.googlecode.com/svn/trunk@5284 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/src/gpu/effects/GrConfigConversionEffect.h b/src/gpu/effects/GrConfigConversionEffect.h
new file mode 100644
index 0000000..9bb7e3a
--- /dev/null
+++ b/src/gpu/effects/GrConfigConversionEffect.h
@@ -0,0 +1,72 @@
+/*
+ * Copyright 2012 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#ifndef GrConfigConversionEffect_DEFINED
+#define GrConfigConversionEffect_DEFINED
+
+#include "GrSingleTextureEffect.h"
+
+class GrGLConfigConversionEffect;
+
+/**
+ * This class is used to perform config conversions. Clients may want to read/write data that is
+ * unpremultiplied. Also on some systems reading/writing BGRA or RGBA is faster. In those cases we
+ * read/write using the faster path and perform an R/B swap in the shader if the client data is in
+ * the slower config.
+ */
+class GrConfigConversionEffect : public GrSingleTextureEffect {
+public:
+ /**
+ * The PM->UPM or UPM->PM conversions to apply.
+ */
+ enum PMConversion {
+ kNone_PMConversion = 0,
+ kMulByAlpha_RoundUp_PMConversion,
+ kMulByAlpha_RoundDown_PMConversion,
+ kDivByAlpha_RoundUp_PMConversion,
+ kDivByAlpha_RoundDown_PMConversion,
+
+ kPMConversionCnt
+ };
+
+ // This will fail if the config is not 8888 and a PM conversion is requested.
+ static GrCustomStage* Create(GrTexture*,
+ bool swapRedAndBlue,
+ PMConversion pmConversion = kNone_PMConversion);
+
+ static const char* Name() { return "Config Conversion"; }
+ typedef GrGLConfigConversionEffect GLProgramStage;
+
+ virtual const GrProgramStageFactory& getFactory() const SK_OVERRIDE;
+ virtual bool isEqual(const GrCustomStage&) const SK_OVERRIDE;
+
+ bool swapsRedAndBlue() const { return fSwapRedAndBlue; }
+ PMConversion pmConversion() const { return fPMConversion; }
+
+ // This function determines whether it is possible to choose PM->UPM and UPM->PM conversions
+ // for which in any PM->UPM->PM->UPM sequence the two UPM values are the same. This means that
+ // if pixels are read back to a UPM buffer, written back to PM to the GPU, and read back again
+ // both reads will produce the same result. This test is quite expensive and should not be run
+ // multiple times for a given context.
+ static void TestForPreservingPMConversions(GrContext* context,
+ PMConversion* PMToUPMRule,
+ PMConversion* UPMToPMRule);
+
+private:
+ GrConfigConversionEffect(GrTexture*,
+ bool swapRedAndBlue,
+ PMConversion pmConversion);
+
+ bool fSwapRedAndBlue;
+ PMConversion fPMConversion;
+
+ GR_DECLARE_CUSTOM_STAGE_TEST;
+
+ typedef GrSingleTextureEffect INHERITED;
+};
+
+#endif