diff -r 000000000000 -r 6474c204b198 gfx/skia/trunk/src/core/SkDeviceLooper.cpp
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/gfx/skia/trunk/src/core/SkDeviceLooper.cpp	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,131 @@
+/*
+ * Copyright 2013 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "SkDeviceLooper.h"
+
+SkDeviceLooper::SkDeviceLooper(const SkBitmap& base,
+                               const SkRasterClip& rc,
+                               const SkIRect& bounds, bool aa)
+: fBaseBitmap(base)
+, fBaseRC(rc)
+, fDelta(aa ? kAA_Delta : kBW_Delta)
+{
+    // sentinels that next() has not yet been called, and so our mapper functions
+    // should not be called either.
+    fCurrBitmap = NULL;
+    fCurrRC = NULL;
+
+    if (!rc.isEmpty()) {
+        // clip must be contained by the bitmap
+        SkASSERT(SkIRect::MakeWH(base.width(), base.height()).contains(rc.getBounds()));
+    }
+
+    if (rc.isEmpty() || !fClippedBounds.intersect(bounds, rc.getBounds())) {
+        fState = kDone_State;
+    } else if (this->fitsInDelta(fClippedBounds)) {
+        fState = kSimple_State;
+    } else {
+        // back up by 1 DX, so that next() will put us in a correct starting
+        // position.
+        fCurrOffset.set(fClippedBounds.left() - fDelta,
+                        fClippedBounds.top());
+        fState = kComplex_State;
+    }
+}
+
+SkDeviceLooper::~SkDeviceLooper() {
+}
+
+void SkDeviceLooper::mapRect(SkRect* dst, const SkRect& src) const {
+    SkASSERT(kDone_State != fState);
+    SkASSERT(fCurrBitmap);
+    SkASSERT(fCurrRC);
+
+    *dst = src;
+    dst->offset(SkIntToScalar(-fCurrOffset.fX),
+                SkIntToScalar(-fCurrOffset.fY));
+}
+
+void SkDeviceLooper::mapMatrix(SkMatrix* dst, const SkMatrix& src) const {
+    SkASSERT(kDone_State != fState);
+    SkASSERT(fCurrBitmap);
+    SkASSERT(fCurrRC);
+
+    *dst = src;
+    dst->postTranslate(SkIntToScalar(-fCurrOffset.fX),
+                       SkIntToScalar(-fCurrOffset.fY));
+}
+
+bool SkDeviceLooper::computeCurrBitmapAndClip() {
+    SkASSERT(kComplex_State == fState);
+
+    SkIRect r = SkIRect::MakeXYWH(fCurrOffset.x(), fCurrOffset.y(),
+                                  fDelta, fDelta);
+    if (!fBaseBitmap.extractSubset(&fSubsetBitmap, r)) {
+        fSubsetRC.setEmpty();
+    } else {
+        fSubsetBitmap.lockPixels();
+        fBaseRC.translate(-r.left(), -r.top(), &fSubsetRC);
+        (void)fSubsetRC.op(SkIRect::MakeWH(fDelta, fDelta),
+                           SkRegion::kIntersect_Op);
+    }
+
+    fCurrBitmap = &fSubsetBitmap;
+    fCurrRC = &fSubsetRC;
+    return !fCurrRC->isEmpty();
+}
+
+static bool next_tile(const SkIRect& boundary, int delta, SkIPoint* offset) {
+    // can we move to the right?
+    if (offset->x() + delta < boundary.right()) {
+        offset->fX += delta;
+        return true;
+    }
+
+    // reset to the left, but move down a row
+    offset->fX = boundary.left();
+    if (offset->y() + delta < boundary.bottom()) {
+        offset->fY += delta;
+        return true;
+    }
+
+    // offset is now outside of boundary, so we're done
+    return false;
+}
+
+bool SkDeviceLooper::next() {
+    switch (fState) {
+        case kDone_State:
+            // in theory, we should not get called here, since we must have
+            // previously returned false, but we check anyway.
+            break;
+
+        case kSimple_State:
+            // first time for simple
+            if (NULL == fCurrBitmap) {
+                fCurrBitmap = &fBaseBitmap;
+                fCurrRC = &fBaseRC;
+                fCurrOffset.set(0, 0);
+                return true;
+            }
+            // 2nd time for simple, we are done
+            break;
+
+        case kComplex_State:
+            // need to propogate fCurrOffset through clippedbounds
+            // left to right, until we wrap around and move down
+
+            while (next_tile(fClippedBounds, fDelta, &fCurrOffset)) {
+                if (this->computeCurrBitmapAndClip()) {
+                    return true;
+                }
+            }
+            break;
+    }
+    fState = kDone_State;
+    return false;
+}