Avoid recomputing two consecutive identical 1D filters.

src/core/SkBitmapScaler.cpp

 #include "SkBitmapScaler.h"
 #include "SkBitmapFilter.h"
 #include "SkRect.h"
 #include "SkTArray.h"
 #include "SkErrorInternals.h"
 #include "SkConvolver.h"
 
 // SkResizeFilter ----------------------------------------------------------------
 
 // Encapsulates computation and storage of the filters required for one complete
@@ skipping 71 matching lines @@
     }
 
 
     float scaleX = static_cast<float>(destWidth) /
                    static_cast<float>(srcFullWidth);
     float scaleY = static_cast<float>(destHeight) /
                    static_cast<float>(srcFullHeight);
 
     this->computeFilters(srcFullWidth, destSubset.fLeft, destSubset.width(),
                          scaleX, &fXFilter, convolveProcs);
-    this->computeFilters(srcFullHeight, destSubset.fTop, destSubset.height(),
-                         scaleY, &fYFilter, convolveProcs);
+    if (srcFullWidth == srcFullHeight &&
+        destSubset.fLeft == destSubset.fTop &&
+        destSubset.width() == destSubset.height()&&
+        scaleX == scaleY) {
+        fYFilter = fXFilter;
+    } else {
+        this->computeFilters(srcFullHeight, destSubset.fTop, destSubset.height(),
+                          scaleY, &fYFilter, convolveProcs);
+    }
 }
 
 // TODO(egouriou): Take advantage of periods in the convolution.
 // Practical resizing filters are periodic outside of the border area.
 // For Lanczos, a scaling by a (reduced) factor of p/q (q pixels in the
 // source become p pixels in the destination) will have a period of p.
 // A nice consequence is a period of 1 when downscaling by an integral
 // factor. Downscaling from typical display resolutions is also bound
 // to produce interesting periods as those are chosen to have multiple
 // small factors.
@@ skipping 210 matching lines @@
 bool SkBitmapScaler::Resize(SkBitmap* resultPtr,
                             const SkBitmap& source,
                             ResizeMethod method,
                             int destWidth, int destHeight,
                             const SkConvolutionProcs& convolveProcs,
                             SkBitmap::Allocator* allocator) {
     SkIRect destSubset = { 0, 0, destWidth, destHeight };
     return Resize(resultPtr, source, method, destWidth, destHeight, destSubset,
                   convolveProcs, allocator);
 }