simplify/unify xferproc api

src/core/SkXfermode.cpp

 /*
  * 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.
  */
 
 #include "SkXfermode.h"
 #include "SkXfermode_proccoeff.h"
 #include "SkColorPriv.h"
@@ skipping 910 matching lines @@
     x.store(pm4.fVec);
     return pm4;
 }
 
 static Sk4f as_4f(const SkPM4f& pm4) {
     return Sk4f::Load(pm4.fVec);
 }
 
 static void assert_unit(const SkPM4f& r) {
 #ifdef SK_DEBUG
-    const float min = 0;
-    const float max = 1;
+    const float eps = 0.00001f;
+    const float min = 0 - eps;
+    const float max = 1 + eps;
     for (int i = 0; i < 4; ++i) {
         SkASSERT(r.fVec[i] >= min && r.fVec[i] <= max);
     }
 #endif
 }
 
 template <Sk4f (blend)(const Sk4f&, const Sk4f&)> SkPM4f proc_4f(const SkPM4f& s, const SkPM4f& d) {
     assert_unit(s);
     assert_unit(d);
     SkPM4f r = as_pm4f(blend(as_4f(s), as_4f(d)));
@@ skipping 466 matching lines @@
     if (!xfer) {
         return SkXfermode::kOpaque_SrcColorOpacity == opacityType;
     }
 
     return xfer->isOpaque(opacityType);
 }
 
 SK_DEFINE_FLATTENABLE_REGISTRAR_GROUP_START(SkXfermode)
     SK_DEFINE_FLATTENABLE_REGISTRAR_ENTRY(SkProcCoeffXfermode)
 SK_DEFINE_FLATTENABLE_REGISTRAR_GROUP_END