Add drawBitmapLattice() API

include/core/SkCanvas.h

Index: include/core/SkCanvas.h
diff --git a/include/core/SkCanvas.h b/include/core/SkCanvas.h
index b6d0cc704af73c917b56ac7392d7a96ddacf58a1..87ca0e4d8b6042942a90261a24306e14b0dc873d 100644
--- a/include/core/SkCanvas.h
+++ b/include/core/SkCanvas.h
@@ -912,7 +912,7 @@ public:
                         SrcRectConstraint = kStrict_SrcRectConstraint);
 
     /**
-     *  Draw the bitmap stretched differentially to fit into dst.
+     *  Draw the bitmap stretched or shrunk differentially to fit into dst.
      *  center is a rect within the bitmap, and logically divides the bitmap
      *  into 9 sections (3x3). For example, if the middle pixel of a [5x5]
      *  bitmap is the "center", then the center-rect should be [2, 2, 3, 3].
@@ -928,6 +928,45 @@ public:
     void drawBitmapNine(const SkBitmap& bitmap, const SkIRect& center, const SkRect& dst,
                         const SkPaint* paint = NULL);
 
+    /**
+     *  Specifies coordinates to divide a bitmap into (xCount*yCount) patches.
+     */
+    struct NinePatchDivs {
+        // An array of x-coordinates that divide the bitmap vertically.
+        // These must be unique, increasing, and in the set [0, width].
+        // Does not have ownership.
+        uint32_t* fXDivs;

[reed1, 2016/05/19 18:21:01]

I would make all of these int instead of uint32_t, mostly just to make the
general skia style.

+
+        // The number of fXDivs.
+        uint32_t  fXCount;
+
+        // An array of y-coordinates that divide the bitmap horiztonally.
+        // These must be unique, increasing, and in the set [0, height].
+        // Does not have ownership.
+        uint32_t* fYDivs;
+
+        // The number of fYDivs.
+        uint32_t  fYCount;
+    };
+
+    /**
+     *  Draw the bitmap stretched or shrunk differentially to fit into dst.
+     *
+     *  Moving horizontally across the bitmap alternating patches will be "scalable"
+     *  (in the x-dimension) to fit into dst or must be left "fixed".  The first patch

[f(malita), 2016/05/19 19:24:20]

The last patch is also fixed, right?

[msarett, 2016/05/19 19:30:58]

In the Android implementation, it really depends on the number of patches, since
they just alternate between "fixed" and "scalable".

In practical use cases, I think it is almost always:
First and last patch are both fixed
OR
First non-empty patch is scalable and last patch is also scalable

[f(malita), 2016/05/19 19:36:11]

Ah, that makes sense (I didn't parse the "alternating" bit off the bat).

+     *  is treated as "fixed", but it's possible to specify an empty first patch by
+     *  making divs.fXDivs[0] = 0.
+     *
+     *  The scale factor for all "scalable" patches will be the same, and may be greater
+     *  than or less than 1 (meaning we can stretch or shrink).  If the number of
+     *  "fixed" pixels is greater than the width of the dst, we will collapse all of
+     *  the "scalable" regions and appropriately downscale the "fixed" regions.
+     *
+     *  The same interpretation also applies the y-dimension.
+     */
+    void drawBitmapNine(const SkBitmap& bitmap, const NinePatchDivs& divs, const SkRect& dst,
+                        const SkPaint* paint = nullptr);
+
     /** Draw the text, with origin at (x,y), using the specified paint.
         The origin is interpreted based on the Align setting in the paint.
         @param text The text to be drawn