New SVG turbulence in Skia

include/effects/SkPerlinNoiseShader.h

Index: include/effects/SkPerlinNoiseShader.h
===================================================================
--- include/effects/SkPerlinNoiseShader.h	(revision 0)
+++ include/effects/SkPerlinNoiseShader.h	(revision 0)
@@ -0,0 +1,111 @@
+/*
+ * Copyright 2013 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#ifndef SkPerlinNoiseShader_DEFINED
+#define SkPerlinNoiseShader_DEFINED
+
+#include "SkShader.h"
+
+/** \class SkPerlinNoiseShader
+
+    SkPerlinNoiseShader creates an image using the Perlin turbulence function.
+
+    It can produce tileable noise if asked to stitch tiles and provided a tile size.
+    In order to fill a large area with repeating noise, set the stitchTiles flag to
+    true, and render exactly a single tile of noise. Without this flag, the result
+    will contain visible seams between tiles.
+
+    The algorithm used is described here :
+    http://www.w3.org/TR/SVG/filters.html#feTurbulenceElement
+*/
+class SkPerlinNoiseShader : public SkShader {
+    struct PaintingData;
+public:
+    struct StitchData;
+
+    /**
+     *  About the noise types : the difference between the 2 is just minor tweaks to the algorithm,
+     *  they're not 2 entirely different noises. The output looks different, but once the noise is
+     *  generated in the [1, -1] range, the output is brought back in the [0, 1] range by doing :
+     *  kFractalNoise_Type : noise * 0.5 + 0.5
+     *  kTurbulence_Type   : abs(noise)
+     *  Very little differences between the 2 types, although you can tell the difference visually.
+     */
+    enum Type {
+        kFractalNoise_Type,
+        kTurbulence_Type,
+        kFirstType = kFractalNoise_Type,
+        kLastType = kTurbulence_Type
+    };
+    /**
+     *  This will construct Perlin noise of the given type (Fractal Noise or Turbulence).
+     *
+     *  Both base frequencies (X and Y) have a usual range of (0..1).
+     *
+     *  The number of octaves provided should be fairly small, although no limit is enforced.
+     *  Each octave doubles the frequency, so 10 octaves would produce noise from
+     *  baseFrequency * 1, * 2, * 4, ..., * 512, which quickly yields insignificantly small
+     *  periods and resembles regular unstructured noise rather than Perlin noise.
+     *
+     *  If tileSize isn't NULL or an empty size, the tileSize parameter will be used to modify
+     *  the frequencies so that the noise will be tileable for the given tile size. If tileSize
+     *  is NULL or an empty size, the frequencies will be used as is without modification.
+     */
+    static SkShader* CreateFractalNoise(SkScalar baseFrequencyX, SkScalar baseFrequencyY,
+                                        int numOctaves, SkScalar seed,
+                                        const SkISize* tileSize = NULL);
+    static SkShader* CreateTubulence(SkScalar baseFrequencyX, SkScalar baseFrequencyY,
+                                     int numOctaves, SkScalar seed,
+                                     const SkISize* tileSize = NULL);
+
+    virtual bool setContext(const SkBitmap& device, const SkPaint& paint,
+                            const SkMatrix& matrix);
+    virtual void shadeSpan(int x, int y, SkPMColor[], int count) SK_OVERRIDE;
+    virtual void shadeSpan16(int x, int y, uint16_t[], int count) SK_OVERRIDE;
+
+    virtual GrEffectRef* asNewEffect(GrContext* context, const SkPaint&) const SK_OVERRIDE;
+
+    SK_DEVELOPER_TO_STRING()
+    SK_DECLARE_PUBLIC_FLATTENABLE_DESERIALIZATION_PROCS(SkPerlinNoiseShader)
+
+protected:
+    SkPerlinNoiseShader(SkFlattenableReadBuffer&);
+    virtual void flatten(SkFlattenableWriteBuffer&) const SK_OVERRIDE;
+
+private:
+    SkPerlinNoiseShader(SkPerlinNoiseShader::Type type, SkScalar baseFrequencyX,
+                        SkScalar baseFrequencyY, int numOctaves, SkScalar seed,
+                        const SkISize* tileSize = NULL);
+    virtual ~SkPerlinNoiseShader();
+
+    void setTileSize(const SkISize&);
+
+    void initPaint(PaintingData& paintingData);
+
+    SkScalar noise2D(int channel, const PaintingData& paintingData,
+                     const StitchData& stitchData, const SkPoint& noiseVector);
+
+    SkScalar calculateTurbulenceValueForPoint(int channel, const PaintingData& paintingData,
+                                              StitchData& stitchData, const SkPoint& point);
+
+    SkPMColor shade(const SkPoint& point, StitchData& stitchData);
+
+    SkPerlinNoiseShader::Type fType;
+    SkScalar fBaseFrequencyX;
+    SkScalar fBaseFrequencyY;
+    int fNumOctaves;
+    SkScalar fSeed;
+    SkISize fTileSize;
+    bool fStitchTiles;
+    SkMatrix fMatrix;
+
+    PaintingData* fPaintingData;
+
+    typedef SkShader INHERITED;
+};
+
+#endif