SkPatch abstraction

include/core/SkPatch.h

+/*
+ * Copyright 2014 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#ifndef SkPatch_DEFINED
+#define SkPatch_DEFINED
+
+#include "SkColor.h"
+#include "SkPoint.h"
+
+class SkFwDCubicEvaluator {
+
+public:
+    SkFwDCubicEvaluator(){ }
+
+    /**
+     * Receives the 4 control points for the cubic.
+     */
+    SkFwDCubicEvaluator(SkPoint a, SkPoint b, SkPoint c, SkPoint d);
+    
+    /**
+     * Resets the forward differences evaluator to the first value of t = 0.
+     */
+    void reset(int res);

[egdaniel, 2014/07/22 19:09:36]

what exactly is the meaning behind res? Maybe I just don't understand exactly
what the forward difference is doing. Maybe give a description of what this
class is actually doing (and forward differencing) and how you derived the
various equations used in reset and other functions

[dandov, 2014/07/22 20:23:28]

I changed the name to divisions meaning the number of times that the cubic is
divided into and added a brief explanation of how they work. 

+
+    /*
+     * Evaluate cubic bezier using forward differences.
+     * Call operator* to check if the next value is still within the range t=[0,1].
+     * Call operator++ to obtain the SkPoint sampled at the next t.
+     * Call reset to start sampling from t=0
+     */
+    inline bool operator*() {

[egdaniel, 2014/07/22 19:09:35]

The * operator seems weird to be used as a bool (usually we use it to actually
get an object). Maybe call this done() or something?

Also is this even actually used anywhere? Seems like the evaluator is only used
inside of setData() in SkPatch and here it looks like you are just looping over
the x and y resolutions so you know when it is done. Maybe we just remove this? 

[dandov, 2014/07/22 20:23:28]

I adjusted the operator* to get the current value and added a method done to
have a way of knowing if the evaluator has finished. Not sure if I will use it. 

+        return fCurrent <= fMax;
+    }
+    
+    inline SkPoint operator++() {
+        SkPoint point = fFwDiff[0];
+        fFwDiff[0]    += fFwDiff[1];
+        fFwDiff[1]    += fFwDiff[2];
+        fFwDiff[2]    += fFwDiff[3];
+        fCurrent++;
+        return point;
+    }
+    
+    inline SkPoint operator++(int) {
+        //repeat this code? inline is affected if not?
+        SkPoint point = fFwDiff[0];
+        fFwDiff[0]    += fFwDiff[1];
+        fFwDiff[1]    += fFwDiff[2];
+        fFwDiff[2]    += fFwDiff[3];
+        fCurrent++;
+        return point;
+    }
+    
+    const SkPoint* getPoints();
+
+    const SkPoint* getCoefs();

[egdaniel, 2014/07/22 19:09:35]

Do you have a need for getCoefs() or getResolution()? I don't see them getting
called anywhere. Are they things you know you will need later as you hook this
in? No reason to add code that is not needed.

[dandov, 2014/07/22 20:23:28]

Done.

+
+    int getResolution();
+
+private:
+    int fMax, fCurrent, fRes;
+    SkPoint fFwDiff[4], fCoefs[4], fPoints[4];
+};
+
+/**
+ * Class that represents a coons patch.
+ */
+class SK_API SkPatch {
+
+public:
+    /*
+     * Points are in the following order:
+     *              (bottom curve)
+     *               0 1 2 3
+     * (left curve)  8     10   (right curve)
+     *               9     11
+     *               4 5 6 7  
+     *              (top curve)
+     * Used pointer to an array to guarantee that this method receives an array of 4 SkColors
+     */
+    SkPatch(SkPoint points[12], SkColor (*colors)[4], int res);
+
+    ~SkPatch();
+
+    void clean();
+
+    const SkPoint* getTopPoints()    { return fTop.getPoints(); }
+
+    const SkPoint* getLeftPoints()   { return fLeft.getPoints(); }
+
+    const SkPoint* getRightPoints()  { return fRight.getPoints(); }
+
+    const SkPoint* getBottomPoints() { return fBottom.getPoints(); }
+
+    void setData();
+
+    int getVertexCount() { return fVertCount; }
+    int getIndexCount() { return fIndexCount; }
+    SkPoint* getPoints()    { return fPoints; }
+    SkPoint* getTexCoords() { return fTexCoords; }
+    uint32_t* getColors()   { return fColors; }
+    uint16_t* getIndices()  { return fIndices; }
+
+private:
+    SkPoint* fCtrlPoints;
+    SkFwDCubicEvaluator fBottom, fTop, fLeft, fRight;
+    SkPMColor fCornerColors[4];
+    int fResX, fResY;
+
+    int fVertCount, fIndexCount;
+    SkPoint* fPoints;
+    SkPoint* fTexCoords;
+    uint32_t* fColors;
+    uint16_t* fIndices;
+    bool fIsSet;
+
+    typedef SkPatch INHERITED;
+};
+
+#endif