Add drawBitmapLattice() API

src/core/SkLatticeIter.cpp

Index: src/core/SkLatticeIter.cpp
diff --git a/src/core/SkLatticeIter.cpp b/src/core/SkLatticeIter.cpp
new file mode 100644
index 0000000000000000000000000000000000000000..24ab3f1cbc29a11af6ded16de3965c93ac76b292
--- /dev/null
+++ b/src/core/SkLatticeIter.cpp
@@ -0,0 +1,230 @@
+/*
+ * Copyright 2015 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "SkLatticeIter.h"
+#include "SkRect.h"
+
+/**
+ *  Divs must be in increasing order with no duplicates.
+ */
+static bool valid_divs(const int* divs, int count, int len) {
+    if (count <= 0) {
+        return false;
+    }
+
+    int prev = -1;
+    for (int i = 0; i < count; i++) {
+        if (prev >= divs[i] || divs[i] > len) {
+            return false;
+        }
+    }
+
+    return true;
+}
+
+bool SkLatticeIter::Valid(int width, int height, const SkCanvas::Lattice& lattice) {
+    return valid_divs(lattice.fXDivs, lattice.fXCount, width) &&
+           valid_divs(lattice.fYDivs, lattice.fYCount, height);
+}
+
+/**
+ *  Count the number of pixels that are in "scalable" patches.
+ */
+static int count_scalable_pixels(const int32_t* divs, int numDivs, bool firstIsScalable,
+                                 int length) {
+    if (0 == numDivs) {
+        return firstIsScalable ? length : 0;
+    }
+
+    int i;
+    int count;
+    if (firstIsScalable) {
+        count = divs[0];
+        i = 1;
+    } else {
+        count = 0;
+        i = 0;
+    }
+
+    for (; i < numDivs; i += 2) {
+        // Alternatively, we could use |top| and |bottom| as variable names, instead of
+        // |left| and |right|.
+        int left = divs[i];
+        int right = (i + 1 < numDivs) ? divs[i + 1] : length;
+        count += right - left;
+    }
+
+    return count;
+}
+
+/**
+ *  Set points for the src and dst rects on subsequent draw calls.
+ */
+static void set_points(float* dst, float* src, const int* divs, int divCount, int srcFixed,
+                       int srcScalable, float dstStart, float dstStop, bool isScalable) {
+
+    float dstLen = dstStop - dstStart;
+    int srcLen = srcFixed + srcScalable;
+    float scale;
+    if (srcFixed <= dstLen) {
+        // This is the "normal" case, where we scale the "scalable" patches and leave
+        // the other patches fixed.
+        scale = (dstLen - ((float) srcFixed)) / ((float) srcScalable);
+    } else {
+        // In this case, we eliminate the "scalable" patches and scale the "fixed" patches.
+        scale = dstLen / ((float) srcFixed);
+    }
+
+    src[0] = 0.0f;
+    dst[0] = dstStart;
+    for (int i = 0; i < divCount; i++) {
+        src[i + 1] = (float) (divs[i]);
+        float srcDelta = src[i + 1] - src[i];
+        float dstDelta;
+        if (srcFixed <= dstLen) {
+            dstDelta = isScalable ? scale * srcDelta : srcDelta;
+        } else {
+            dstDelta = isScalable ? 0.0f : scale * srcDelta;
+        }
+        dst[i + 1] = dst[i] + dstDelta;
+
+        // Alternate between "scalable" and "fixed" patches.
+        isScalable = !isScalable;
+    }
+
+    src[divCount + 1] = (float) srcLen;
+    dst[divCount + 1] = dstStop;
+}
+
+SkLatticeIter::SkLatticeIter(int srcWidth, int srcHeight, const SkCanvas::Lattice& lattice,
+                             const SkRect& dst)
+{
+    const int* xDivs = lattice.fXDivs;
+    int xCount = lattice.fXCount;
+    const int* yDivs = lattice.fYDivs;
+    int yCount = lattice.fYCount;
+
+    // In the x-dimension, the first rectangle always starts at x = 0 and is "scalable".
+    // If xDiv[0] is 0, it indicates that the first rectangle is degenerate, so the
+    // first real rectangle "scalable" in the x-direction.
+    //
+    // The same interpretation applies to the y-dimension.
+    //
+    // As we move left to right across the image, alternating patches will be "fixed" or
+    // "scalable" in the x-direction.  Similarly, as move top to bottom, alternating
+    // patches will be "fixed" or "scalable" in the y-direction.
+    SkASSERT(xCount > 0 && yCount > 0);
+    bool xIsScalable = (0 == xDivs[0]);
+    if (xIsScalable) {
+        // Once we've decided that the first patch is "scalable", we don't need the
+        // xDiv.  It is always implied that we start at zero.
+        xDivs++;
+        xCount--;
+    }
+    bool yIsScalable = (0 == yDivs[0]);
+    if (yIsScalable) {
+        // Once we've decided that the first patch is "scalable", we don't need the
+        // yDiv.  It is always implied that we start at zero.
+        yDivs++;
+        yCount--;
+    }
+
+    // We never need the final xDiv/yDiv if it is equal to the width/height.  This is implied.
+    if (xCount > 0 && srcWidth == xDivs[xCount - 1]) {
+        xCount--;
+    }
+    if (yCount > 0 && srcHeight == yDivs[yCount - 1]) {
+        yCount--;
+    }
+
+    // Count "scalable" and "fixed" pixels in each dimension.
+    int xCountScalable = count_scalable_pixels(xDivs, xCount, xIsScalable, srcWidth);
+    int xCountFixed = srcWidth - xCountScalable;
+    int yCountScalable = count_scalable_pixels(yDivs, yCount, yIsScalable, srcHeight);
+    int yCountFixed = srcHeight - yCountScalable;
+
+    fSrcX.reset(xCount + 2);
+    fDstX.reset(xCount + 2);
+    set_points(fDstX.begin(), fSrcX.begin(), xDivs, xCount, xCountFixed, xCountScalable,
+               dst.fLeft, dst.fRight, xIsScalable);
+
+    fSrcY.reset(yCount + 2);
+    fDstY.reset(yCount + 2);
+    set_points(fDstY.begin(), fSrcY.begin(), yDivs, yCount, yCountFixed, yCountScalable,
+               dst.fTop, dst.fBottom, yIsScalable);
+
+    fCurrX = fCurrY = 0;
+    fDone = false;
+}
+
+bool SkLatticeIter::Valid(int width, int height, const SkIRect& center) {
+    return !center.isEmpty() && SkIRect::MakeWH(width, height).contains(center);
+}
+
+SkLatticeIter::SkLatticeIter(int w, int h, const SkIRect& c, const SkRect& dst) {
+    SkASSERT(SkIRect::MakeWH(w, h).contains(c));
+
+    fSrcX.reset(4);
+    fSrcY.reset(4);
+    fDstX.reset(4);
+    fDstY.reset(4);
+
+    fSrcX[0] = 0;
+    fSrcX[1] = SkIntToScalar(c.fLeft);
+    fSrcX[2] = SkIntToScalar(c.fRight);
+    fSrcX[3] = SkIntToScalar(w);
+
+    fSrcY[0] = 0;
+    fSrcY[1] = SkIntToScalar(c.fTop);
+    fSrcY[2] = SkIntToScalar(c.fBottom);
+    fSrcY[3] = SkIntToScalar(h);
+
+    fDstX[0] = dst.fLeft;
+    fDstX[1] = dst.fLeft + SkIntToScalar(c.fLeft);
+    fDstX[2] = dst.fRight - SkIntToScalar(w - c.fRight);
+    fDstX[3] = dst.fRight;
+
+    fDstY[0] = dst.fTop;
+    fDstY[1] = dst.fTop + SkIntToScalar(c.fTop);
+    fDstY[2] = dst.fBottom - SkIntToScalar(h - c.fBottom);
+    fDstY[3] = dst.fBottom;
+
+    if (fDstX[1] > fDstX[2]) {
+        fDstX[1] = fDstX[0] + (fDstX[3] - fDstX[0]) * c.fLeft / (w - c.width());
+        fDstX[2] = fDstX[1];
+    }
+
+    if (fDstY[1] > fDstY[2]) {
+        fDstY[1] = fDstY[0] + (fDstY[3] - fDstY[0]) * c.fTop / (h - c.height());
+        fDstY[2] = fDstY[1];
+    }
+
+    fCurrX = fCurrY = 0;
+    fDone = false;
+}
+
+bool SkLatticeIter::next(SkRect* src, SkRect* dst) {
+    if (fDone) {
+        return false;
+    }
+
+    const int x = fCurrX;
+    const int y = fCurrY;
+    SkASSERT(x >= 0 && x < fSrcX.count() - 1);
+    SkASSERT(y >= 0 && y < fSrcY.count() - 1);
+
+    src->set(fSrcX[x], fSrcY[y], fSrcX[x + 1], fSrcY[y + 1]);
+    dst->set(fDstX[x], fDstY[y], fDstX[x + 1], fDstY[y + 1]);
+    if (fSrcX.count() - 1 == ++fCurrX) {
+        fCurrX = 0;
+        fCurrY += 1;
+        if (fCurrY >= fSrcY.count() - 1) {
+            fDone = true;
+        }
+    }
+    return true;
+}