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Avoid overflowing coverage in rasterizer

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A single examined pixel might have sampled corners outside the logical
constraints, that needs to be ignore.

Pick-to: 6.4 6.3 6.2
Fixes: QTBUG-92485
Change-Id: I105fd42d3388a48f3bb03c00d640832e8e99477c
Reviewed-by: Eirik Aavitsland <eirik.aavitsland@qt.io>
This commit is contained in:
Allan Sandfeld Jensen 2022-06-25 11:59:20 +02:00
parent 3709bc3699
commit aefb5c5a56
1 changed files with 8 additions and 11 deletions
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19
src/gui/painting/qrasterizer.cpp
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@ -1064,28 +1064,26 @@ void QRasterizer::rasterizeLine(const QPointF &a, const QPointF &b, qreal width,
while (x <= leftMax) { while (x <= leftMax) {
QScFixed excluded = 0; QScFixed excluded = 0;
if (yFP <= iLeftFP) if (yFP <= iLeftFP && rowBottomLeft > rowTop)
excluded += intersectPixelFP(x, rowTop, rowBottomLeft, excluded += intersectPixelFP(x, rowTop, rowBottomLeft,
bottomLeftIntersectAf, topLeftIntersectAf, bottomLeftIntersectAf, topLeftIntersectAf,
topLeftSlopeFP, invTopLeftSlopeFP); topLeftSlopeFP, invTopLeftSlopeFP);
if (yFP >= iLeftFP) if (yFP >= iLeftFP && rowBottom > rowTopLeft)
excluded += intersectPixelFP(x, rowTopLeft, rowBottom, excluded += intersectPixelFP(x, rowTopLeft, rowBottom,
topLeftIntersectBf, bottomLeftIntersectBf, topLeftIntersectBf, bottomLeftIntersectBf,
bottomLeftSlopeFP, invBottomLeftSlopeFP); bottomLeftSlopeFP, invBottomLeftSlopeFP);
if (x >= rightMin) { if (x >= rightMin) {
if (yFP <= iRightFP) if (yFP <= iRightFP && rowBottomRight > rowTop)
excluded += (rowBottomRight - rowTop) - intersectPixelFP(x, rowTop, rowBottomRight, excluded += (rowBottomRight - rowTop) - intersectPixelFP(x, rowTop, rowBottomRight,
topRightIntersectAf, bottomRightIntersectAf, topRightIntersectAf, bottomRightIntersectAf,
topRightSlopeFP, invTopRightSlopeFP); topRightSlopeFP, invTopRightSlopeFP);
if (yFP >= iRightFP) if (yFP >= iRightFP && rowBottom > rowTopRight)
excluded += (rowBottom - rowTopRight) - intersectPixelFP(x, rowTopRight, rowBottom, excluded += (rowBottom - rowTopRight) - intersectPixelFP(x, rowTopRight, rowBottom,
bottomRightIntersectBf, topRightIntersectBf, bottomRightIntersectBf, topRightIntersectBf,
bottomRightSlopeFP, invBottomRightSlopeFP); bottomRightSlopeFP, invBottomRightSlopeFP);
} }
if (excluded > QScFixedFactor)
excluded = excluded % QScFixedFactor;
Q_ASSERT(excluded >= 0 && excluded <= rowHeight);
QScFixed coverage = rowHeight - excluded; QScFixed coverage = rowHeight - excluded;
buffer.addSpan(x, 1, QScFixedToInt(yFP), buffer.addSpan(x, 1, QScFixedToInt(yFP),
QScFixedToInt(255 * coverage)); QScFixedToInt(255 * coverage));
@ -1098,17 +1096,16 @@ void QRasterizer::rasterizeLine(const QPointF &a, const QPointF &b, qreal width,
} }
while (x <= rightMax) { while (x <= rightMax) {
QScFixed excluded = 0; QScFixed excluded = 0;
if (yFP <= iRightFP) if (yFP <= iRightFP && rowBottomRight > rowTop)
excluded += (rowBottomRight - rowTop) - intersectPixelFP(x, rowTop, rowBottomRight, excluded += (rowBottomRight - rowTop) - intersectPixelFP(x, rowTop, rowBottomRight,
topRightIntersectAf, bottomRightIntersectAf, topRightIntersectAf, bottomRightIntersectAf,
topRightSlopeFP, invTopRightSlopeFP); topRightSlopeFP, invTopRightSlopeFP);
if (yFP >= iRightFP) if (yFP >= iRightFP && rowBottom > rowTopRight)
excluded += (rowBottom - rowTopRight) - intersectPixelFP(x, rowTopRight, rowBottom, excluded += (rowBottom - rowTopRight) - intersectPixelFP(x, rowTopRight, rowBottom,
bottomRightIntersectBf, topRightIntersectBf, bottomRightIntersectBf, topRightIntersectBf,
bottomRightSlopeFP, invBottomRightSlopeFP); bottomRightSlopeFP, invBottomRightSlopeFP);
if (excluded > QScFixedFactor)
excluded = excluded % QScFixedFactor;
Q_ASSERT(excluded >= 0 && excluded <= rowHeight);
QScFixed coverage = rowHeight - excluded; QScFixed coverage = rowHeight - excluded;
buffer.addSpan(x, 1, QScFixedToInt(yFP), buffer.addSpan(x, 1, QScFixedToInt(yFP),
QScFixedToInt(255 * coverage)); QScFixedToInt(255 * coverage));