Remove the need for asCoeff in SkXfermode.

src/core/SkDraw.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 "SkDraw.h"
 #include "SkBlitter.h"
 #include "SkCanvas.h"
@@ skipping 918 matching lines @@
 
 static SkScalar fast_len(const SkVector& vec) {
     SkScalar x = SkScalarAbs(vec.fX);
     SkScalar y = SkScalarAbs(vec.fY);
     if (x < y) {
         SkTSwap(x, y);
     }
     return x + SkScalarHalf(y);
 }
 
-static bool xfermodeSupportsCoverageAsAlpha(SkXfermode* xfer) {
-    SkXfermode::Coeff dc;
-    if (!SkXfermode::AsCoeff(xfer, NULL, &dc)) {
-        return false;
-    }
-
-    switch (dc) {
-        case SkXfermode::kOne_Coeff:
-        case SkXfermode::kISA_Coeff:
-        case SkXfermode::kISC_Coeff:
-            return true;
-        default:
-            return false;
-    }
-}
-
 bool SkDrawTreatAAStrokeAsHairline(SkScalar strokeWidth, const SkMatrix& matrix,
                                    SkScalar* coverage) {
     SkASSERT(strokeWidth > 0);
     // We need to try to fake a thick-stroke with a modulated hairline.
 
     if (matrix.hasPerspective()) {
         return false;
     }
 
     SkVector src[2], dst[2];
@@ skipping 91 matching lines @@
     // at this point we're done with prePathMatrix
     SkDEBUGCODE(prePathMatrix = (const SkMatrix*)0x50FF8001;)
 
     SkTCopyOnFirstWrite<SkPaint> paint(origPaint);
 
     {
         SkScalar coverage;
         if (SkDrawTreatAsHairline(origPaint, *matrix, &coverage)) {
             if (SK_Scalar1 == coverage) {
                 paint.writable()->setStrokeWidth(0);
-            } else if (xfermodeSupportsCoverageAsAlpha(origPaint.getXfermode())) {
+            } else if (SkXfermode::SupportsCoverageAsAlpha(origPaint.getXfermode())) {
                 U8CPU newAlpha;
 #if 0
                 newAlpha = SkToU8(SkScalarRoundToInt(coverage *
                                                      origPaint.getAlpha()));
 #else
                 // this is the old technique, which we preserve for now so
                 // we don't change previous results (testing)
                 // the new way seems fine, its just (a tiny bit) different
                 int scale = (int)SkScalarMul(coverage, 256);
                 newAlpha = origPaint.getAlpha() * scale >> 8;
@@ skipping 1321 matching lines @@
         mask->fImage = SkMask::AllocImage(size);
         memset(mask->fImage, 0, mask->computeImageSize());
     }
 
     if (SkMask::kJustComputeBounds_CreateMode != mode) {
         draw_into_mask(*mask, devPath, style);
     }
 
     return true;
 }