Further refactor read/writeSurfacePixels

Detect the situation where we're going to want to do PM/UPM, and want to
use GrConfigConverionEffect, but be unable (due to the lack of a
round-trip pair). This lets us hoist the SW premul work (in
writeSurfacePixels), and avoid all the cascading failure logic in both
functions. (We never try to create the PM/UPM effects unless we know
that they're going to work).

Bug: skia:5853
Change-Id: I0077447cd4be93bba273f8d2826b1ec0f4915c6c
Reviewed-on: https://skia-review.googlesource.com/13592
Commit-Queue: Brian Osman <brianosman@google.com>
Reviewed-by: Robert Phillips <robertphillips@google.com>

1 files changed, 13 insertions, 11 deletions

diff --git a/include/gpu/GrContext.h b/include/gpu/GrContext.h
index f2ba24d4db..08198beb59 100644
--- a/include/gpu/GrContext.h
+++ b/include/gpu/GrContext.h
@@ -346,18 +346,20 @@ private:
     void initCommon(const GrContextOptions&);
 
     /**
-     * These functions create premul <-> unpremul effects if it is possible to generate a pair
-     * of effects that make a readToUPM->writeToPM->readToUPM cycle invariant. Otherwise, they
-     * return NULL. They also can perform a swizzle as part of the draw.
+     * These functions create premul <-> unpremul effects. If the second argument is 'true', they
+     * use the specialized round-trip effects from GrConfigConversionEffect, otherwise they
+     * create effects that do naive multiply or divide.
      */
-    sk_sp<GrFragmentProcessor> createPMToUPMEffect(sk_sp<GrFragmentProcessor>, GrPixelConfig);
-    sk_sp<GrFragmentProcessor> createUPMToPMEffect(sk_sp<GrFragmentProcessor>, GrPixelConfig);
-    /** Called before either of the above two functions to determine the appropriate fragment
-        processors for conversions. */
-    void testPMConversionsIfNecessary(uint32_t flags);
-    /** Returns true if we've determined that createPMtoUPMEffect and createUPMToPMEffect will
-        succeed for the passed in config. Otherwise we fall back to SW conversion. */
-    bool validPMUPMConversionExists(GrPixelConfig) const;
+    sk_sp<GrFragmentProcessor> createPMToUPMEffect(sk_sp<GrFragmentProcessor>,
+                                                   bool useConfigConversionEffect);
+    sk_sp<GrFragmentProcessor> createUPMToPMEffect(sk_sp<GrFragmentProcessor>,
+                                                   bool useConfigConversionEffect);
+
+    /**
+     * Returns true if createPMtoUPMEffect and createUPMToPMEffect will succeed for non-sRGB 8888
+     * configs. In other words, did we find a pair of round-trip preserving conversion effects?
+     */
+    bool validPMUPMConversionExists();
 
     /**
      * A callback similar to the above for use by the TextBlobCache