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 "SkPreConfig.h"
+#include "SkPoint.h"
+
+/**
+ * Class that represents a coons patch.
+ */
+class SK_API SkPatch {
+
+public:
+    /**
+     * Structure that holds the vertex data related to the tessellation of a SkPatch. It is passed 
+     * as a parameter to the function getVertexData which sets the points, colors and texture 
+     * coordinates of the vertices and the indices for them to be drawn as triangles.
+     */
+    struct PatchData {
+        int fVertexCount, fIndexCount;
+        SkPoint* fPoints;
+        SkPoint* fTexCoords;
+        uint32_t* fColors;
+        uint16_t* fIndices;
+        
+        PatchData()
+        : fVertexCount(0)
+        , fIndexCount(0)
+        , fPoints(NULL)
+        , fTexCoords(NULL)
+        , fColors(NULL)
+        , fIndices(NULL) { }
+        
+        ~PatchData() {
+            SkDELETE_ARRAY(fPoints);
+            SkDELETE_ARRAY(fTexCoords);
+            SkDELETE_ARRAY(fColors);
+            SkDELETE_ARRAY(fIndices);
+        }
+    };
+    
+    enum CubicCtrlPts {
+        kTopP0_CubicCtrlPts = 0,
+        kTopP1_CubicCtrlPts = 1,
+        kTopP2_CubicCtrlPts = 2,
+        kTopP3_CubicCtrlPts = 3,
+        
+        kRightP0_CubicCtrlPts = 3,
+        kRightP1_CubicCtrlPts = 4,
+        kRightP2_CubicCtrlPts = 5,
+        kRightP3_CubicCtrlPts = 6,
+        
+        kBottomP0_CubicCtrlPts = 9,
+        kBottomP1_CubicCtrlPts = 8,
+        kBottomP2_CubicCtrlPts = 7,
+        kBottomP3_CubicCtrlPts = 6,
+        
+        kLeftP0_CubicCtrlPts = 0,
+        kLeftP1_CubicCtrlPts = 11,
+        kLeftP2_CubicCtrlPts = 10,
+        kLeftP3_CubicCtrlPts = 9,
+    };
+    
+    /**
+     * Points are in the following order:
+     *              (top curve)
+     *                0 1 2 3
+     * (left curve)  11     4   (right curve)
+     *               10     5
+     *                9 8 7 6
+     *              (bottom curve)
+     * Used pointer to an array to guarantee that this method receives an array of 4 SkColors
+     */
+    SkPatch(SkPoint points[12], SkColor colors[4]);

[bsalomon, 2014/07/25 15:18:08]

Not a suggestion for this patch, but I wonder whether we should have explicit
colors at all. That seems like one of many ways that the interpolation can be
used. We could say this always produces texture/local coordinates when it is
rendered and an SkShader could be used to do bilerp between 4 colors. Just a
thought.

+
+    /**
+     * Function that evaluates the coons patch interpolation.
+     * data refers to the pointer of the PatchData struct in which the tessellation data is set.
+     * divisions defines the number of steps in which the SkPatch is going to be subdivided per
+     * axis.
+     */
+    bool getVertexData(SkPatch::PatchData* data, int divisions);
+
+    void getTopPoints(SkPoint points[4]) {
+        points[0] = fCtrlPoints[kTopP0_CubicCtrlPts];
+        points[1] = fCtrlPoints[kTopP1_CubicCtrlPts];
+        points[2] = fCtrlPoints[kTopP2_CubicCtrlPts];
+        points[3] = fCtrlPoints[kTopP3_CubicCtrlPts];
+    }
+    
+    const void getBottomPoints(SkPoint points[4]) {
+        points[0] = fCtrlPoints[kBottomP0_CubicCtrlPts];
+        points[1] = fCtrlPoints[kBottomP1_CubicCtrlPts];
+        points[2] = fCtrlPoints[kBottomP2_CubicCtrlPts];
+        points[3] = fCtrlPoints[kBottomP3_CubicCtrlPts];
+    }
+
+    const void getLeftPoints(SkPoint points[4]) {
+        points[0] = fCtrlPoints[kLeftP0_CubicCtrlPts];
+        points[1] = fCtrlPoints[kLeftP1_CubicCtrlPts];
+        points[2] = fCtrlPoints[kLeftP2_CubicCtrlPts];
+        points[3] = fCtrlPoints[kLeftP3_CubicCtrlPts];
+    }
+
+    const void getRightPoints(SkPoint points[4]) {
+        points[0] = fCtrlPoints[kRightP0_CubicCtrlPts];
+        points[1] = fCtrlPoints[kRightP1_CubicCtrlPts];
+        points[2] = fCtrlPoints[kRightP2_CubicCtrlPts];
+        points[3] = fCtrlPoints[kRightP3_CubicCtrlPts];
+    }
+    
+private:
+    SkPoint fCtrlPoints[12];
+    SkPMColor fCornerColors[4];
+};
+
+#endif