Don't create a GXPFactory when blend is SrcOver

include/core/SkXfermode.h

 
 /*
  * Copyright 2006 The Android Open Source Project
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 
 #ifndef SkXfermode_DEFINED
@@ skipping 186 matching lines @@
         GrFragmentProcessor. The input to the returned FP is the src color. The dst color is
         provided by the dst param which becomes a child FP of the returned FP. If the params are
         null then this is just a query of whether the SkXfermode could support this functionality.
         It is legal for the function to succeed but return a null output. This indicates that
         the output of the blend is simply the src color.
      */
     virtual bool asFragmentProcessor(const GrFragmentProcessor** output,
                                      const GrFragmentProcessor* dst) const;
 
     /** A subclass may implement this factory function to work with the GPU backend. It is legal
-        to call this with xpf NULL to simply test the return value. If xpf is non-NULL then the
-        xfermode may optionally allocate a factory to return to the caller as *xpf. The caller
-        will install it and own a ref to it. Since the xfermode may or may not assign *xpf, the
-        caller should set *xpf to NULL beforehand. XferProcessors cannot use a background texture.
-     */
+      to call this with xpf NULL to simply test the return value. If xpf is non-NULL then the
+      xfermode may optionally allocate a factory to return to the caller as *xpf. The caller
+      will install it and own a ref to it. Since the xfermode may or may not assign *xpf, the
+      caller should set *xpf to NULL beforehand. XferProcessors cannot use a background texture.
+      */
     virtual bool asXPFactory(GrXPFactory** xpf) const;
 
     /** Returns true if the xfermode can be expressed as an xfer processor factory (xpFactory).
-        This helper calls the asXPFactory() virtual. If the xfermode is NULL, it is treated as
-        kSrcOver_Mode. It is legal to call this with xpf param NULL to simply test the return value.
-     */
-    static bool AsXPFactory(SkXfermode*, GrXPFactory**);
+      This helper calls the asXPFactory() virtual. If the xfermode is NULL, it is treated as
+      kSrcOver_Mode. It is legal to call this with xpf param NULL to simply test the return value.
+      */
+    static inline bool AsXPFactory(SkXfermode* xfermode, GrXPFactory** xpf) {
+        if (nullptr == xfermode) {
+            if (xpf) {
+                *xpf = nullptr;
+            }
+            return true;
+        }
+        return xfermode->asXPFactory(xpf);
+    }
 
     SK_TO_STRING_PUREVIRT()
     SK_DECLARE_FLATTENABLE_REGISTRAR_GROUP()
     SK_DEFINE_FLATTENABLE_TYPE(SkXfermode)
 
 protected:
     SkXfermode() {}
     /** The default implementation of xfer32/xfer16/xferA8 in turn call this
         method, 1 color at a time (upscaled to a SkPMColor). The default
         implementation of this method just returns dst. If performance is
         important, your subclass should override xfer32/xfer16/xferA8 directly.
 
         This method will not be called directly by the client, so it need not
         be implemented if your subclass has overridden xfer32/xfer16/xferA8
     */
     virtual SkPMColor xferColor(SkPMColor src, SkPMColor dst) const;
 
 private:
     enum {
         kModeCount = kLastMode + 1
     };
 
     typedef SkFlattenable INHERITED;
 };
 
 #endif