short circuit high quality scales that are actually the identity

src/core/SkBitmapProcState.cpp

 
 /*
  * Copyright 2011 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 #include "SkBitmapProcState.h"
 #include "SkColorPriv.h"
 #include "SkFilterProc.h"
@@ skipping 149 matching lines @@
     // remove the scaling component from the matrix.
 
     if (SkPaint::kHigh_FilterLevel == fFilterLevel &&
         fInvMatrix.getType() <= (SkMatrix::kScale_Mask | SkMatrix::kTranslate_Mask) &&
         kN32_SkColorType == fOrigBitmap.colorType() &&
         cache_size_okay(fOrigBitmap, fInvMatrix)) {
 
         SkScalar invScaleX = fInvMatrix.getScaleX();
         SkScalar invScaleY = fInvMatrix.getScaleY();
 
+        if (SkScalarNearlyEqual(invScaleX,1.0f) &&
+            SkScalarNearlyEqual(invScaleY,1.0f)) {
+            // short-circuit identity scaling; the output is supposed to
+            // be the same as the input, so we might as well go fast.
+
+            // Note(humper): We could also probably do this if the scales
+            // are close to -1 as well, since the flip doesn't require
+            // any fancy re-sampling...
+
+            // Set our filter level to low -- the only post-filtering this
+            // image might require is some interpolation if the translation
+            // is fractional.
+            fFilterLevel = SkPaint::kLow_FilterLevel;
+            return false;
+        }
+
         fScaledCacheID = SkScaledImageCache::FindAndLock(fOrigBitmap,
                                                          invScaleX, invScaleY,
                                                          &fScaledBitmap);
         if (fScaledCacheID) {
             fScaledBitmap.lockPixels();
             if (!fScaledBitmap.getPixels()) {
                 fScaledBitmap.unlockPixels();
                 // found a purged entry (discardablememory?), release it
                 SkScaledImageCache::Unlock(fScaledCacheID);
                 fScaledCacheID = NULL;
@@ skipping 31 matching lines @@
             SkASSERT(NULL != fScaledBitmap.getPixels());
         }
 
         SkASSERT(NULL != fScaledBitmap.getPixels());
         fBitmap = &fScaledBitmap;
 
         // set the inv matrix type to translate-only;
         fInvMatrix.setTranslate(fInvMatrix.getTranslateX() / fInvMatrix.getScaleX(),
                                 fInvMatrix.getTranslateY() / fInvMatrix.getScaleY());
 
-        // no need for any further filtering; we just did it!
-        fFilterLevel = SkPaint::kNone_FilterLevel;
+        // Set our filter level to low -- the only post-filtering this
+        // image might require is some interpolation if the translation
+        // is fractional.
+        fFilterLevel = SkPaint::kLow_FilterLevel;
         unlocker.release();
         return true;
     }
 
     /*
      *  If High, then our special-case for scale-only did not take, and so we
      *  have to make a choice:
      *      1. fall back on mipmaps + bilerp
      *      2. fall back on scanline bicubic filter
      *  For now, we compute the "scale" value from the matrix, and have a
@@ skipping 822 matching lines @@
     } else {
         size >>= 2;
     }
 
     if (fFilterLevel != SkPaint::kNone_FilterLevel) {
         size >>= 1;
     }
 
     return size;
 }