SkTCopyOnFirstWrite

R=reed@google.com
Review URL: https://codereview.appspot.com/6650047

git-svn-id: http://skia.googlecode.com/svn/trunk@5905 2bbb7eff-a529-9590-31e7-b0007b416f81

2 files changed, 13 insertions, 32 deletions

diff --git a/src/core/SkBlitter.cpp b/src/core/SkBlitter.cpp
index 322f91d40d..cdb2b625a7 100644
--- a/src/core/SkBlitter.cpp
+++ b/src/core/SkBlitter.cpp
@@ -847,17 +847,13 @@ SkBlitter* SkBlitter::Choose(const SkBitmap& device,
     SkXfermode* mode = origPaint.getXfermode();
     Sk3DShader* shader3D = NULL;
 
-    SkTLazy<SkPaint> lazyPaint;
-    // we promise not to mutate paint unless we know we've reassigned it from
-    // lazyPaint
-    SkPaint* paint = const_cast<SkPaint*>(&origPaint);
+    SkTCopyOnFirstWrite<SkPaint> paint(origPaint);
 
     if (origPaint.getMaskFilter() != NULL &&
             origPaint.getMaskFilter()->getFormat() == SkMask::k3D_Format) {
         shader3D = SkNEW_ARGS(Sk3DShader, (shader));
         // we know we haven't initialized lazyPaint yet, so just do it
-        paint = lazyPaint.set(origPaint);
-        paint->setShader(shader3D)->unref();
+        paint.writable()->setShader(shader3D)->unref();
         shader = shader3D;
     }
 
@@ -865,10 +861,7 @@ SkBlitter* SkBlitter::Choose(const SkBitmap& device,
         switch (interpret_xfermode(*paint, mode, device.config())) {
             case kSrcOver_XferInterp:
                 mode = NULL;
-                if (!lazyPaint.isValid()) {
-                    paint = lazyPaint.set(origPaint);
-                }
-                paint->setXfermode(NULL);
+                paint.writable()->setXfermode(NULL);
                 break;
             case kSkipDrawing_XferInterp:
                 SK_PLACEMENT_NEW(blitter, SkNullBlitter, storage, storageSize);
@@ -886,18 +879,13 @@ SkBlitter* SkBlitter::Choose(const SkBitmap& device,
 #endif
             // xfermodes (and filters) require shaders for our current blitters
             shader = SkNEW(SkColorShader);
-            if (!lazyPaint.isValid()) {
-                paint = lazyPaint.set(origPaint);
-            }
-            paint->setShader(shader)->unref();
+            paint.writable()->setShader(shader)->unref();
         } else if (cf) {
             // if no shader && no xfermode, we just apply the colorfilter to
             // our color and move on.
-            if (!lazyPaint.isValid()) {
-                paint = lazyPaint.set(origPaint);
-            }
-            paint->setColor(cf->filterColor(paint->getColor()));
-            paint->setColorFilter(NULL);
+            SkPaint* writablePaint = paint.writable();
+            writablePaint->setColor(cf->filterColor(paint->getColor()));
+            writablePaint->setColorFilter(NULL);
             cf = NULL;
         }
     }
@@ -905,10 +893,7 @@ SkBlitter* SkBlitter::Choose(const SkBitmap& device,
     if (cf) {
         SkASSERT(shader);
         shader = SkNEW_ARGS(SkFilterShader, (shader, cf));
-        if (!lazyPaint.isValid()) {
-            paint = lazyPaint.set(origPaint);
-        }
-        paint->setShader(shader)->unref();
+        paint.writable()->setShader(shader)->unref();
         // blitters should ignore the presence/absence of a filter, since
         // if there is one, the shader will take care of it.
     }
diff --git a/src/core/SkDraw.cpp b/src/core/SkDraw.cpp
index cdd59c1cdb..885a810836 100644
--- a/src/core/SkDraw.cpp
+++ b/src/core/SkDraw.cpp
@@ -931,16 +931,13 @@ void SkDraw::drawPath(const SkPath& origSrcPath, const SkPaint& origPaint,
     // at this point we're done with prePathMatrix
     SkDEBUGCODE(prePathMatrix = (const SkMatrix*)0x50FF8001;)
 
-    const SkPaint* paint = &origPaint;
-    SkTLazy<SkPaint> lazyPaint;
+    SkTCopyOnFirstWrite<SkPaint> paint(origPaint);
 
     {
         SkScalar coverage;
         if (SkDrawTreatAsHairline(origPaint, *matrix, &coverage)) {
             if (SK_Scalar1 == coverage) {
-                lazyPaint.set(origPaint);
-                lazyPaint.get()->setStrokeWidth(0);
-                paint = lazyPaint.get();
+                paint.writable()->setStrokeWidth(0);
             } else if (xfermodeSupportsCoverageAsAlpha(origPaint.getXfermode())) {
                 U8CPU newAlpha;
 #if 0
@@ -953,10 +950,9 @@ void SkDraw::drawPath(const SkPath& origSrcPath, const SkPaint& origPaint,
                 int scale = (int)SkScalarMul(coverage, 256);
                 newAlpha = origPaint.getAlpha() * scale >> 8;
 #endif
-                lazyPaint.set(origPaint);
-                lazyPaint.get()->setStrokeWidth(0);
-                lazyPaint.get()->setAlpha(newAlpha);
-                paint = lazyPaint.get();
+                SkPaint* writablePaint = paint.writable();
+                writablePaint->setStrokeWidth(0);
+                writablePaint->setAlpha(newAlpha);
             }
         }
     }