always scale to an integer; compensate for fractional image sizes by leaving the fractional scale i…

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 "SkBitmapCache.h"
 #include "SkBitmapProcState.h"
 #include "SkColorPriv.h"
@@ skipping 131 matching lines @@
         < (maximumAllocation * invMat.getScaleX() * invMat.getScaleY());
 }
 
 // TODO -- we may want to pass the clip into this function so we only scale
 // the portion of the image that we're going to need.  This will complicate
 // the interface to the cache, but might be well worth it.
 
 bool SkBitmapProcState::possiblyScaleImage() {
     SkASSERT(NULL == fBitmap);
 
+    fAdjustedMatrix = false;
+
     if (fFilterLevel <= SkPaint::kLow_FilterLevel) {
         return false;
     }
     // Check to see if the transformation matrix is simple, and if we're
     // doing high quality scaling.  If so, do the bitmap scale here and
-    // remove the scaling component from the matrix.
+    // remove the (non-fractional) scaling component from the matrix.
+
+    SkScalar invScaleX = fInvMatrix.getScaleX();
+    SkScalar invScaleY = fInvMatrix.getScaleY();
+
+    float trueDestWidth  = fOrigBitmap.width() / invScaleX;
+    float trueDestHeight = fOrigBitmap.height() / invScaleY;
+
+#ifndef SK_IGNORE_PROPER_FRACTIONAL_SCALING
+    float roundedDestWidth = SkScalarRoundToScalar(trueDestWidth);
+    float roundedDestHeight = SkScalarRoundToScalar(trueDestHeight);
+#else
+    float roundedDestWidth = trueDestWidth;
+    float roundedDestHeight = trueDestHeight;
+#endif
 
     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;
         }
 
-        if (!SkBitmapCache::Find(fOrigBitmap, invScaleX, invScaleY, &fScaledBitmap)) {
-            float dest_width  = fOrigBitmap.width() / invScaleX;
-            float dest_height = fOrigBitmap.height() / invScaleY;
-
+        if (!SkBitmapCache::Find(fOrigBitmap, roundedDestWidth, roundedDestHeight, &fScaledBitmap)) {
             // All the criteria are met; let's make a new bitmap.
 
             if (!SkBitmapScaler::Resize(&fScaledBitmap,
                                         fOrigBitmap,
                                         SkBitmapScaler::RESIZE_BEST,
-                                        dest_width,
-                                        dest_height,
+                                        roundedDestWidth,
+                                        roundedDestHeight,
                                         SkScaledImageCache::GetAllocator())) {
                 // we failed to create fScaledBitmap, so just return and let
                 // the scanline proc handle it.
                 return false;
 
             }
 
             SkASSERT(NULL != fScaledBitmap.getPixels());
-            SkBitmapCache::Add(fOrigBitmap, invScaleX, invScaleY, fScaledBitmap);
+            SkBitmapCache::Add(fOrigBitmap, roundedDestWidth, roundedDestHeight, fScaledBitmap);
         }
 
         SkASSERT(NULL != fScaledBitmap.getPixels());
         fBitmap = &fScaledBitmap;
 
         // set the inv matrix type to translate-only;
         fInvMatrix.setTranslate(fInvMatrix.getTranslateX() / fInvMatrix.getScaleX(),
                                 fInvMatrix.getTranslateY() / fInvMatrix.getScaleY());
 
+#ifndef SK_IGNORE_PROPER_FRACTIONAL_SCALING
+        // reintroduce any fractional scaling missed by our integral scale done above.
+
+        float fractionalScaleX = trueDestWidth/roundedDestWidth;
+        float fractionalScaleY = trueDestHeight/roundedDestHeight;
+
+        fInvMatrix.postScale(fractionalScaleX, fractionalScaleY);
+#endif
+        fAdjustedMatrix = true;
+
         // Set our filter level to low -- the only post-filtering this
         // image might require is some interpolation if the translation
-        // is fractional.
+        // is fractional or if there's any remaining scaling to be done.
         fFilterLevel = SkPaint::kLow_FilterLevel;
         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 135 matching lines @@
     // If we are "still" kMedium_FilterLevel, then the request was not fulfilled by possiblyScale,
     // so we downgrade to kLow (so the rest of the sniffing code can assume that)
     if (SkPaint::kMedium_FilterLevel == fFilterLevel) {
         fFilterLevel = SkPaint::kLow_FilterLevel;
     }
 
     bool trivialMatrix = (fInvMatrix.getType() & ~SkMatrix::kTranslate_Mask) == 0;
     bool clampClamp = SkShader::kClamp_TileMode == fTileModeX &&
                       SkShader::kClamp_TileMode == fTileModeY;
 
-    if (!(clampClamp || trivialMatrix)) {
+    if (!(fAdjustedMatrix || clampClamp || trivialMatrix)) {
         fInvMatrix.postIDiv(fOrigBitmap.width(), fOrigBitmap.height());
     }
 
     // Now that all possible changes to the matrix have taken place, check
     // to see if we're really close to a no-scale matrix.  If so, explicitly
     // set it to be so.  Subsequent code may inspect this matrix to choose
     // a faster path in this case.
 
     // This code will only execute if the matrix has some scale component;
     // if it's already pure translate then we won't do this inversion.
@@ skipping 626 matching lines @@
     } else {
         size >>= 2;
     }
 
     if (fFilterLevel != SkPaint::kNone_FilterLevel) {
         size >>= 1;
     }
 
     return size;
 }