diff -r 000000000000 -r 6474c204b198 gfx/skia/trunk/src/core/SkLineClipper.cpp
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/gfx/skia/trunk/src/core/SkLineClipper.cpp	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,283 @@
+
+/*
+ * Copyright 2011 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+#include "SkLineClipper.h"
+
+template <typename T> T pin_unsorted(T value, T limit0, T limit1) {
+    if (limit1 < limit0) {
+        SkTSwap(limit0, limit1);
+    }
+    // now the limits are sorted
+    SkASSERT(limit0 <= limit1);
+
+    if (value < limit0) {
+        value = limit0;
+    } else if (value > limit1) {
+        value = limit1;
+    }
+    return value;
+}
+
+// return X coordinate of intersection with horizontal line at Y
+static SkScalar sect_with_horizontal(const SkPoint src[2], SkScalar Y) {
+    SkScalar dy = src[1].fY - src[0].fY;
+    if (SkScalarNearlyZero(dy)) {
+        return SkScalarAve(src[0].fX, src[1].fX);
+    } else {
+        // need the extra precision so we don't compute a value that exceeds
+        // our original limits
+        double X0 = src[0].fX;
+        double Y0 = src[0].fY;
+        double X1 = src[1].fX;
+        double Y1 = src[1].fY;
+        double result = X0 + ((double)Y - Y0) * (X1 - X0) / (Y1 - Y0);
+
+        // The computed X value might still exceed [X0..X1] due to quantum flux
+        // when the doubles were added and subtracted, so we have to pin the
+        // answer :(
+        return (float)pin_unsorted(result, X0, X1);
+    }
+}
+
+// return Y coordinate of intersection with vertical line at X
+static SkScalar sect_with_vertical(const SkPoint src[2], SkScalar X) {
+    SkScalar dx = src[1].fX - src[0].fX;
+    if (SkScalarNearlyZero(dx)) {
+        return SkScalarAve(src[0].fY, src[1].fY);
+    } else {
+        // need the extra precision so we don't compute a value that exceeds
+        // our original limits
+        double X0 = src[0].fX;
+        double Y0 = src[0].fY;
+        double X1 = src[1].fX;
+        double Y1 = src[1].fY;
+        double result = Y0 + ((double)X - X0) * (Y1 - Y0) / (X1 - X0);
+        return (float)result;
+    }
+}
+
+///////////////////////////////////////////////////////////////////////////////
+
+static inline bool nestedLT(SkScalar a, SkScalar b, SkScalar dim) {
+    return a <= b && (a < b || dim > 0);
+}
+
+// returns true if outer contains inner, even if inner is empty.
+// note: outer.contains(inner) always returns false if inner is empty.
+static inline bool containsNoEmptyCheck(const SkRect& outer,
+                                        const SkRect& inner) {
+    return  outer.fLeft <= inner.fLeft && outer.fTop <= inner.fTop &&
+            outer.fRight >= inner.fRight && outer.fBottom >= inner.fBottom;
+}
+
+bool SkLineClipper::IntersectLine(const SkPoint src[2], const SkRect& clip,
+                                  SkPoint dst[2]) {
+    SkRect bounds;
+
+    bounds.set(src, 2);
+    if (containsNoEmptyCheck(clip, bounds)) {
+        if (src != dst) {
+            memcpy(dst, src, 2 * sizeof(SkPoint));
+        }
+        return true;
+    }
+    // check for no overlap, and only permit coincident edges if the line
+    // and the edge are colinear
+    if (nestedLT(bounds.fRight, clip.fLeft, bounds.width()) ||
+        nestedLT(clip.fRight, bounds.fLeft, bounds.width()) ||
+        nestedLT(bounds.fBottom, clip.fTop, bounds.height()) ||
+        nestedLT(clip.fBottom, bounds.fTop, bounds.height())) {
+        return false;
+    }
+
+    int index0, index1;
+
+    if (src[0].fY < src[1].fY) {
+        index0 = 0;
+        index1 = 1;
+    } else {
+        index0 = 1;
+        index1 = 0;
+    }
+
+    SkPoint tmp[2];
+    memcpy(tmp, src, sizeof(tmp));
+
+    // now compute Y intersections
+    if (tmp[index0].fY < clip.fTop) {
+        tmp[index0].set(sect_with_horizontal(src, clip.fTop), clip.fTop);
+    }
+    if (tmp[index1].fY > clip.fBottom) {
+        tmp[index1].set(sect_with_horizontal(src, clip.fBottom), clip.fBottom);
+    }
+
+    if (tmp[0].fX < tmp[1].fX) {
+        index0 = 0;
+        index1 = 1;
+    } else {
+        index0 = 1;
+        index1 = 0;
+    }
+
+    // check for quick-reject in X again, now that we may have been chopped
+    if ((tmp[index1].fX <= clip.fLeft || tmp[index0].fX >= clip.fRight) &&
+        tmp[index0].fX < tmp[index1].fX) {
+        // only reject if we have a non-zero width
+        return false;
+    }
+
+    if (tmp[index0].fX < clip.fLeft) {
+        tmp[index0].set(clip.fLeft, sect_with_vertical(src, clip.fLeft));
+    }
+    if (tmp[index1].fX > clip.fRight) {
+        tmp[index1].set(clip.fRight, sect_with_vertical(src, clip.fRight));
+    }
+#ifdef SK_DEBUG
+    bounds.set(tmp, 2);
+    SkASSERT(containsNoEmptyCheck(clip, bounds));
+#endif
+    memcpy(dst, tmp, sizeof(tmp));
+    return true;
+}
+
+#ifdef SK_DEBUG
+// return value between the two limits, where the limits are either ascending
+// or descending.
+static bool is_between_unsorted(SkScalar value,
+                                SkScalar limit0, SkScalar limit1) {
+    if (limit0 < limit1) {
+        return limit0 <= value && value <= limit1;
+    } else {
+        return limit1 <= value && value <= limit0;
+    }
+}
+#endif
+
+#ifdef SK_DEBUG
+// This is an example of why we need to pin the result computed in
+// sect_with_horizontal. If we didn't explicitly pin, is_between_unsorted would
+// fail.
+//
+static void sect_with_horizontal_test_for_pin_results() {
+    const SkPoint pts[] = {
+        { -540000,    -720000 },
+        { -9.10000017e-05f, 9.99999996e-13f }
+    };
+    float x = sect_with_horizontal(pts, 0);
+    SkASSERT(is_between_unsorted(x, pts[0].fX, pts[1].fX));
+}
+#endif
+
+int SkLineClipper::ClipLine(const SkPoint pts[], const SkRect& clip,
+                            SkPoint lines[]) {
+#ifdef SK_DEBUG
+    {
+        static bool gOnce;
+        if (!gOnce) {
+            sect_with_horizontal_test_for_pin_results();
+            gOnce = true;
+        }
+    }
+#endif
+
+    int index0, index1;
+
+    if (pts[0].fY < pts[1].fY) {
+        index0 = 0;
+        index1 = 1;
+    } else {
+        index0 = 1;
+        index1 = 0;
+    }
+
+    // Check if we're completely clipped out in Y (above or below
+
+    if (pts[index1].fY <= clip.fTop) {  // we're above the clip
+        return 0;
+    }
+    if (pts[index0].fY >= clip.fBottom) {  // we're below the clip
+        return 0;
+    }
+
+    // Chop in Y to produce a single segment, stored in tmp[0..1]
+
+    SkPoint tmp[2];
+    memcpy(tmp, pts, sizeof(tmp));
+
+    // now compute intersections
+    if (pts[index0].fY < clip.fTop) {
+        tmp[index0].set(sect_with_horizontal(pts, clip.fTop), clip.fTop);
+        SkASSERT(is_between_unsorted(tmp[index0].fX, pts[0].fX, pts[1].fX));
+    }
+    if (tmp[index1].fY > clip.fBottom) {
+        tmp[index1].set(sect_with_horizontal(pts, clip.fBottom), clip.fBottom);
+        SkASSERT(is_between_unsorted(tmp[index1].fX, pts[0].fX, pts[1].fX));
+    }
+
+    // Chop it into 1..3 segments that are wholly within the clip in X.
+
+    // temp storage for up to 3 segments
+    SkPoint resultStorage[kMaxPoints];
+    SkPoint* result;    // points to our results, either tmp or resultStorage
+    int lineCount = 1;
+    bool reverse;
+
+    if (pts[0].fX < pts[1].fX) {
+        index0 = 0;
+        index1 = 1;
+        reverse = false;
+    } else {
+        index0 = 1;
+        index1 = 0;
+        reverse = true;
+    }
+
+    if (tmp[index1].fX <= clip.fLeft) {  // wholly to the left
+        tmp[0].fX = tmp[1].fX = clip.fLeft;
+        result = tmp;
+        reverse = false;
+    } else if (tmp[index0].fX >= clip.fRight) {    // wholly to the right
+        tmp[0].fX = tmp[1].fX = clip.fRight;
+        result = tmp;
+        reverse = false;
+    } else {
+        result = resultStorage;
+        SkPoint* r = result;
+
+        if (tmp[index0].fX < clip.fLeft) {
+            r->set(clip.fLeft, tmp[index0].fY);
+            r += 1;
+            r->set(clip.fLeft, sect_with_vertical(tmp, clip.fLeft));
+            SkASSERT(is_between_unsorted(r->fY, tmp[0].fY, tmp[1].fY));
+        } else {
+            *r = tmp[index0];
+        }
+        r += 1;
+
+        if (tmp[index1].fX > clip.fRight) {
+            r->set(clip.fRight, sect_with_vertical(tmp, clip.fRight));
+            SkASSERT(is_between_unsorted(r->fY, tmp[0].fY, tmp[1].fY));
+            r += 1;
+            r->set(clip.fRight, tmp[index1].fY);
+        } else {
+            *r = tmp[index1];
+        }
+
+        lineCount = SkToInt(r - result);
+    }
+
+    // Now copy the results into the caller's lines[] parameter
+    if (reverse) {
+        // copy the pts in reverse order to maintain winding order
+        for (int i = 0; i <= lineCount; i++) {
+            lines[lineCount - i] = result[i];
+        }
+    } else {
+        memcpy(lines, result, (lineCount + 1) * sizeof(SkPoint));
+    }
+    return lineCount;
+}