From ac78863acdef4b428aaf66985b80c76d1be0fdea Mon Sep 17 00:00:00 2001 From: caryclark Date: Thu, 22 Sep 2016 05:15:14 -0700 Subject: fix for conic fuzz A fuzzer generates a conic that hangs when drawn. The quads that approximate the conics move up and down in y, confusing the renderer. This fix ensures that the split conic maintains the same y direction as the original conic. R=reed@google.com BUG=647922 GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2350263003 Review-Url: https://codereview.chromium.org/2350263003 --- src/core/SkGeometry.cpp | 32 ++++++++++++++++++++++++++++++++ 1 file changed, 32 insertions(+) (limited to 'src/core') diff --git a/src/core/SkGeometry.cpp b/src/core/SkGeometry.cpp index a3ebfb38a8..027b65f0f1 100644 --- a/src/core/SkGeometry.cpp +++ b/src/core/SkGeometry.cpp @@ -1153,6 +1153,12 @@ int SkConic::computeQuadPOW2(SkScalar tol) const { return pow2; } +// This was originally developed and tested for pathops: see SkOpTypes.h +// returns true if (a <= b <= c) || (a >= b >= c) +static bool between(SkScalar a, SkScalar b, SkScalar c) { + return (a - b) * (c - b) <= 0; +} + static SkPoint* subdivide(const SkConic& src, SkPoint pts[], int level) { SkASSERT(level >= 0); @@ -1162,6 +1168,32 @@ static SkPoint* subdivide(const SkConic& src, SkPoint pts[], int level) { } else { SkConic dst[2]; src.chop(dst); + const SkScalar startY = src.fPts[0].fY; + const SkScalar endY = src.fPts[2].fY; + if (between(startY, src.fPts[1].fY, endY)) { + // If the input is monotonic and the output is not, the scan converter hangs. + // Ensure that the chopped conics maintain their y-order. + SkScalar midY = dst[0].fPts[2].fY; + if (!between(startY, midY, endY)) { + // If the computed midpoint is outside the ends, move it to the closer one. + SkScalar closerY = SkTAbs(midY - startY) < SkTAbs(midY - endY) ? startY : endY; + dst[0].fPts[2].fY = dst[1].fPts[0].fY = closerY; + } + if (!between(startY, dst[0].fPts[1].fY, dst[0].fPts[2].fY)) { + // If the 1st control is not between the start and end, put it at the start. + // This also reduces the quad to a line. + dst[0].fPts[1].fY = startY; + } + if (!between(dst[1].fPts[0].fY, dst[1].fPts[1].fY, endY)) { + // If the 2nd control is not between the start and end, put it at the end. + // This also reduces the quad to a line. + dst[1].fPts[1].fY = endY; + } + // Verify that all five points are in order. + SkASSERT(between(startY, dst[0].fPts[1].fY, dst[0].fPts[2].fY)); + SkASSERT(between(dst[0].fPts[1].fY, dst[0].fPts[2].fY, dst[1].fPts[1].fY)); + SkASSERT(between(dst[0].fPts[2].fY, dst[1].fPts[1].fY, endY)); + } --level; pts = subdivide(dst[0], pts, level); return subdivide(dst[1], pts, level); -- cgit v1.2.3