SkPatchGrid interface (after SkPatch/SkPicture rebase).

src/effects/gradients/SkMeshGradient.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 SkMeshGradient_DEFINED
+#define SkMeshGradient_DEFINED
+
+#include "SkPatch.h"
+#include "SkCanvas.h"
+
+/**
+ * Class that represents a Mesh Gradient. A mesh gradient is an array of coons patches, adjacent 
+ * patches share their corners and a color is specified at each one of them. The colors are 
+ * bilinearly interpolated across the patch.
+ *
+ * This implementation defines a bidimensional array of patches. There are 3 arrays to store the 
+ * control points of the patches to avoid storing repeated data since there are several points
+ * shared between adjacent patches. 
+ *
+ * The array fCornerPts stores the corner control points of the patches.
+ * The array fHrzPts holds the intermidiate control points of the top and bottom curves of a patch.
+ * The array fVrtPts holds the intermidiate control points of the left and right curves of a patch.
+ * The array fCornerColors holds the corner colors in the same format as fCornerPts.
+ * The array fExists holds bools to determine if there is an existing patch at a certain location of

[egdaniel, 2014/08/07 17:58:55]

Can remove the comments about fExists

[dandov, 2014/08/07 18:11:46]

Done.

+ * the grid. 
+ *
+ *   fExists              fCornerPts               fHrzPts                  fVrtPts
+ *   -------            --------------       -------------------         --------------
+ *  | 1 | 1 |          | C0 | C1 | C2 |     | H0 | H1 | H2 | H3 |       | V0 | V1 | V2 |
+ *   -------            --------------       ------------------         ---------------
+ *  | 1 | 1 |          | C3 | C4 | C5 |     | H4 | H5 | H6 | H7 |       | V4 | V5 | V6 |
+ *   -------            --------------       -------------------         --------------
+ *                     | C6 | C7 | C8 |     | H8 | H9 | H10| H11|       | V6 | V7 | V8 |
+ *                      --------------       -------------------         --------------
+ *                                                                      | V9 | V10| V11|
+ *                                                                       --------------
+ *
+ * With the above configuration we would have a 2x2 grid of patches:
+ *               H0     H1 H2   H3
+ *              /        \/      \
+ *              C0-------C1-------C2
+ *             /|        |        |\
+ *           v0 |        v1       | v2
+ *           v3 |        V4       | v5
+ *             \|        |        |/
+ *              C3-H4-H5-C4-H6-H7-C5
+ *             /|        |        |\
+ *           v6 |        v7       | v8
+ *           v9 |        v10      | v11
+ *             \|        |        |/
+ *              C6-------C7-------C8
+ *               \      / \      /
+ *                H8   H9  H10  H11
+ *
+ * When trying to get a patch at a certain position it justs builds it with the corresponding 
+ * points.
+ * When adding a patch it tries to add the points at their corresponding position trying to comply
+ * with the adjacent points or overwriting them.
+ * 
+ * Based the idea on the SVG2 spec: 
+ * <meshGradient x="100" y="100">
+ *      <meshRow>
+ *          <meshPatch>
+ *              <stop .../>
+ *              Up to four stops in first patch. See details below.
+ *          </meshPatch>
+ *          <meshPatch>
+ *              Any number of meshPatches in row.
+ *          </meshPatch>
+ *      </meshRow>
+ *      <meshRow>
+ *          Any number of meshRows, each with the same number of meshPatches as in the first row.
+ *      </meshRow>
+ </meshGradient>
+ */
+class SkMeshGradient {
+    
+public:
+    SkMeshGradient(int rows, int cols);
+    SkMeshGradient(int rows, int cols, const SkPoint* corners, const SkPoint* hrzCtrlPts,
+                   const SkPoint* vrtCtrlPts, const SkColor* colors);
+    
+    ~SkMeshGradient();
+    
+    /**
+     * Add a patch at location (x,y). The function returns false if none of the new patch's control
+     * points are set, which may be because (x,y) are out of range or because the patch already
+     * exists at the given location and overwrite was set to false.

[egdaniel, 2014/08/07 17:58:55]

what is overwrite here?

[dandov, 2014/08/07 18:11:46]

Forgot to fix some of the comments. Overwrite was a flag to keep values of
adjacent patches instead of directly overwriting them, but now that is gone. 

+     * If overwrite is true then the patch is always set and overwrites the values of adjacent
+     * patches. If it is set to false and the location is empty the function just set the control
+     * that are "empty" meaning that it does not overwrite values of adjacent patches.
+     */
+    bool addPatch(int x, int y, const SkPatch& patch);
+    bool addPatch(int x, int y, const SkPoint ctrlPts[12], const SkColor colors[4]);
+    
+    /**
+     * Get patch at location (x,y). If the patch is not NULL it sets patch's
+     * control points and colors to the corresponding values.
+     */
+    void getPatchAt(int x, int y, SkPatch* patch) const;
+    
+    /**
+     * Resizes the mesh gradient to contain the given rows and cols of patches.
+     * The function copies the values of the previous patches that are still within the new ranges.
+     */
+    void resize(int rows, int cols);

[egdaniel, 2014/08/07 17:58:55]

Do you have a plan to use this function? My gut instinct tells me we would know
the size of the mesh at start and wouldn't need to change it ever

[dandov, 2014/08/07 18:11:46]

I was thinking for a similar case as Illustrator's editor in which you click
inside the mesh and it gets subdivided at that point, maybe a subdivide function
that subdivides the mesh at a point by creating 4 patches based on the previous
corners and the new point? or just remove the function?

+    
+    /**
+     * Resets the mesh gradient to contain rows and cols of patches. The main difference between
+     * this and resize is that resize keeps the previous values of control points and colors and
+     * this doesn't.
+     */
+    void reset(int rows, int cols, const SkPoint* corners, const SkPoint* hrzCtrlPts,
+               const SkPoint* vrtCtrlPts, const SkColor* colors);
+    
+    /**
+     * Draws the mesh gradient.
+     */
+    void draw(SkCanvas* canvas, SkPaint& paint);
+    
+    /**
+     * Get the dimensions of the grid of patches.
+     */
+    SkISize getDimensions() const {
+        return SkISize::Make(fCols, fRows);
+    }
+    
+private:
+    int fRows, fCols;
+    SkPoint* fCornerPts;
+    SkColor* fCornerColors;
+    SkPoint* fHrzCtrlPts;
+    SkPoint* fVrtCtrlPts;
+};
+
+
+#endif