check for identity in translate

src/core/SkCanvas.cpp

 /*
  * Copyright 2008 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 "SkBitmapDevice.h"
 #include "SkCanvas.h"
 #include "SkCanvasPriv.h"
@@ skipping 1439 matching lines @@
             dstDev->drawDevice(iter, srcDev, pos.x(), pos.y(), *paint);
         }
     }
 
     LOOPER_END
 }
 
 /////////////////////////////////////////////////////////////////////////////
 
 void SkCanvas::translate(SkScalar dx, SkScalar dy) {
-    this->checkForDeferredSave();
-    fDeviceCMDirty = true;
-    fMCRec->fMatrix.preTranslate(dx,dy);
+    if (dx || dy) {
+        this->checkForDeferredSave();
+        fDeviceCMDirty = true;
+        fMCRec->fMatrix.preTranslate(dx,dy);
 
-    // Translate shouldn't affect the is-scale-translateness of the matrix.
-    SkASSERT(fIsScaleTranslate == fMCRec->fMatrix.isScaleTranslate());
+        // Translate shouldn't affect the is-scale-translateness of the matrix.
+        SkASSERT(fIsScaleTranslate == fMCRec->fMatrix.isScaleTranslate());
 
-    this->didTranslate(dx,dy);
+        this->didTranslate(dx,dy);
+    }
 }
 
 void SkCanvas::scale(SkScalar sx, SkScalar sy) {
     SkMatrix m;
     m.setScale(sx, sy);
     this->concat(m);
 }
 
 void SkCanvas::rotate(SkScalar degrees) {
     SkMatrix m;
@@ skipping 2024 matching lines @@
 
 SkAutoCanvasMatrixPaint::~SkAutoCanvasMatrixPaint() {
     fCanvas->restoreToCount(fSaveCount);
 }
 
 #ifdef SK_SUPPORT_LEGACY_NEW_SURFACE_API
 SkSurface* SkCanvas::newSurface(const SkImageInfo& info, const SkSurfaceProps* props) {
     return this->makeSurface(info, props).release();
 }
 #endif