Perform perlin noise matrix computations once per frame, not per pixel.

src/effects/SkPerlinNoiseShader.cpp

 /*
  * Copyright 2013 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkDither.h"
 #include "SkPerlinNoiseShader.h"
 #include "SkColorFilter.h"
@@ skipping 392 matching lines @@
     if (channel == 3) { // Scale alpha by paint value
         turbulenceFunctionResult = SkScalarMul(turbulenceFunctionResult,
             SkScalarDiv(SkIntToScalar(getPaintAlpha()), SkIntToScalar(255)));
     }
 
     // Clamp result
     return SkScalarPin(turbulenceFunctionResult, 0, SK_Scalar1);
 }
 
 SkPMColor SkPerlinNoiseShader::shade(const SkPoint& point, StitchData& stitchData) const {
-    SkMatrix matrix = fMatrix;
-    matrix.postConcat(getLocalMatrix());
-    SkMatrix invMatrix;
-    if (!matrix.invert(&invMatrix)) {
-        invMatrix.reset();
-    } else {
-        invMatrix.postConcat(invMatrix); // Square the matrix
-    }
-    // This (1,1) translation is due to WebKit's 1 based coordinates for the noise
-    // (as opposed to 0 based, usually). The same adjustment is in the setData() function.
-    matrix.postTranslate(SK_Scalar1, SK_Scalar1);
     SkPoint newPoint;
-    matrix.mapPoints(&newPoint, &point, 1);
-    invMatrix.mapPoints(&newPoint, &newPoint, 1);
+    fMatrix.mapPoints(&newPoint, &point, 1);
     newPoint.fX = SkScalarRoundToScalar(newPoint.fX);
     newPoint.fY = SkScalarRoundToScalar(newPoint.fY);
 
     U8CPU rgba[4];
     for (int channel = 3; channel >= 0; --channel) {
         rgba[channel] = SkScalarFloorToInt(255 *
             calculateTurbulenceValueForPoint(channel, *fPaintingData, stitchData, newPoint));
     }
     return SkPreMultiplyARGB(rgba[3], rgba[0], rgba[1], rgba[2]);
 }
 
 bool SkPerlinNoiseShader::setContext(const SkBitmap& device, const SkPaint& paint,
                                      const SkMatrix& matrix) {
-    fMatrix = matrix;
+    SkMatrix newMatrix = matrix;
+    newMatrix.postConcat(getLocalMatrix());
+    SkMatrix invMatrix;
+    if (!newMatrix.invert(&invMatrix)) {
+        invMatrix.reset();
+    }
+    // This (1,1) translation is due to WebKit's 1 based coordinates for the noise
+    // (as opposed to 0 based, usually). The same adjustment is in the setData() function.
+    newMatrix.postTranslate(SK_Scalar1, SK_Scalar1);
+    newMatrix.postConcat(invMatrix);
+    newMatrix.postConcat(invMatrix);
+    fMatrix = newMatrix;
     return INHERITED::setContext(device, paint, matrix);
 }
 
 void SkPerlinNoiseShader::shadeSpan(int x, int y, SkPMColor result[], int count) {
     SkPoint point = SkPoint::Make(SkIntToScalar(x), SkIntToScalar(y));
     StitchData stitchData;
     for (int i = 0; i < count; ++i) {
         result[i] = shade(point, stitchData);
         point.fX += SK_Scalar1;
     }
@@ skipping 896 matching lines @@
     str->append(" seed: ");
     str->appendScalar(fSeed);
     str->append(" stitch tiles: ");
     str->append(fStitchTiles ? "true " : "false ");
 
     this->INHERITED::toString(str);
 
     str->append(")");
 }
 #endif