Revert "replace SkXfermode obj with SkBlendMode enum in paints"

This reverts commit I4fb489ba6b3f77b458f7e4a99f79c7ad10859135.

Reason for revert: <INSERT REASONING HERE>

Original change's description:
> replace SkXfermode obj with SkBlendMode enum in paints
> 
> BUG=skia:5814
> 
> GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2714
> 
> Change-Id: I4fb489ba6b3f77b458f7e4a99f79c7ad10859135
> Reviewed-on: https://skia-review.googlesource.com/2714
> Reviewed-by: Florin Malita <fmalita@chromium.org>
> Reviewed-by: Brian Salomon <bsalomon@google.com>
> Commit-Queue: Mike Reed <reed@google.com>
> 

TBR=bsalomon@google.com,fmalita@chromium.org,fmalita@google.com,reed@google.com,reviews@skia.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true

Change-Id: I3e43f79ef5c1709929663fe63cc1f67cd78270b7
Reviewed-on: https://skia-review.googlesource.com/2871
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Mike Reed <reed@google.com>

1 files changed, 24 insertions, 17 deletions

diff --git a/src/core/SkRecordDraw.cpp b/src/core/SkRecordDraw.cpp
index dca19df100..ca9c1b6f78 100644
--- a/src/core/SkRecordDraw.cpp
+++ b/src/core/SkRecordDraw.cpp
@@ -341,27 +341,34 @@ private:
                 return true;
             }
 
-            // Unusual blendmodes require us to process a saved layer
+            // Unusual Xfermodes require us to process a saved layer
             // even with operations outisde the clip.
             // For example, DstIn is used by masking layers.
             // https://code.google.com/p/skia/issues/detail?id=1291
             // https://crbug.com/401593
-            switch (paint->getBlendMode()) {
-                // For each of the following transfer modes, if the source
-                // alpha is zero (our transparent black), the resulting
-                // blended alpha is not necessarily equal to the original
-                // destination alpha.
-                case SkBlendMode::kClear:
-                case SkBlendMode::kSrc:
-                case SkBlendMode::kSrcIn:
-                case SkBlendMode::kDstIn:
-                case SkBlendMode::kSrcOut:
-                case SkBlendMode::kDstATop:
-                case SkBlendMode::kModulate:
-                    return true;
-                    break;
-                default:
-                    break;
+            SkXfermode* xfermode = paint->getXfermode();
+            SkXfermode::Mode mode;
+            // SrcOver is ok, and is also the common case with a nullptr xfermode.
+            // So we should make that the fast path and bypass the mode extraction
+            // and test.
+            if (xfermode && xfermode->asMode(&mode)) {
+                switch (mode) {
+                    // For each of the following transfer modes, if the source
+                    // alpha is zero (our transparent black), the resulting
+                    // blended alpha is not necessarily equal to the original
+                    // destination alpha.
+                    case SkXfermode::kClear_Mode:
+                    case SkXfermode::kSrc_Mode:
+                    case SkXfermode::kSrcIn_Mode:
+                    case SkXfermode::kDstIn_Mode:
+                    case SkXfermode::kSrcOut_Mode:
+                    case SkXfermode::kDstATop_Mode:
+                    case SkXfermode::kModulate_Mode:
+                        return true;
+                        break;
+                    default:
+                        break;
+                }
             }
         }
         return false;