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Avoid floating point exceptions in rasterizeLine. 

Task-number: QTBUG-16757

Change-Id: I3ef988f1e039c12529d62197d85a62f201e4ae12
Reviewed-by: Lars Knoll <lars.knoll@digia.com>
bb10
Gunnar Sletta 2013-06-11 11:09:34 +02:00 committed by The Qt Project
parent 425af59f53
commit 85b4f0d2d3
1 changed files with 45 additions and 16 deletions
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61
src/gui/painting/qrasterizer.cpp
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@ -734,6 +734,35 @@ static inline QPointF snapTo26Dot6Grid(const QPointF &p)
qFloorF(p.y() * 64) * (1 / qreal(64)));
}
/*
The rasterize line function relies on some div by zero which should
result in +/-inf values. However, when floating point exceptions are
enabled, this will cause crashes, so we return high numbers instead.
As the returned value is used in further arithmetic, returning
FLT_MAX/DBL_MAX will also cause values, so instead return a value
that is well outside the int-range.
*/
static inline qreal qSafeDivide(qreal x, qreal y)
{
if (y == 0)
return x > 0 ? 1e20 : -1e20;
return x / y;
}
/* Conversion to int fails if the value is too large to fit into INT_MAX or
too small to fit into INT_MIN, so we need this slightly safer conversion
when floating point exceptions are enabled
*/
static inline int qSafeFloatToQ16Dot16(qreal x)
{
qreal tmp = x * 65536.;
if (tmp > qreal(INT_MAX))
return INT_MAX;
else if (tmp < qreal(INT_MIN))
return -INT_MAX;
return int(tmp);
}
void QRasterizer::rasterizeLine(const QPointF &a, const QPointF &b, qreal width, bool squareCap)
{
if (a == b || width == 0 || d->clipRect.isEmpty())
@ -946,23 +975,23 @@ void QRasterizer::rasterizeLine(const QPointF &a, const QPointF &b, qreal width,
const QPointF bottomLeftEdge = bottom - left;
const QPointF bottomRightEdge = bottom - right;
const qreal topLeftSlope = topLeftEdge.x() / topLeftEdge.y();
const qreal bottomLeftSlope = bottomLeftEdge.x() / bottomLeftEdge.y();
const qreal topLeftSlope = qSafeDivide(topLeftEdge.x(), topLeftEdge.y());
const qreal bottomLeftSlope = qSafeDivide(bottomLeftEdge.x(), bottomLeftEdge.y());
const qreal topRightSlope = topRightEdge.x() / topRightEdge.y();
const qreal bottomRightSlope = bottomRightEdge.x() / bottomRightEdge.y();
const qreal topRightSlope = qSafeDivide(topRightEdge.x(), topRightEdge.y());
const qreal bottomRightSlope = qSafeDivide(bottomRightEdge.x(), bottomRightEdge.y());
const Q16Dot16 topLeftSlopeFP = FloatToQ16Dot16(topLeftSlope);
const Q16Dot16 topRightSlopeFP = FloatToQ16Dot16(topRightSlope);
const Q16Dot16 topLeftSlopeFP = qSafeFloatToQ16Dot16(topLeftSlope);
const Q16Dot16 topRightSlopeFP = qSafeFloatToQ16Dot16(topRightSlope);
const Q16Dot16 bottomLeftSlopeFP = FloatToQ16Dot16(bottomLeftSlope);
const Q16Dot16 bottomRightSlopeFP = FloatToQ16Dot16(bottomRightSlope);
const Q16Dot16 bottomLeftSlopeFP = qSafeFloatToQ16Dot16(bottomLeftSlope);
const Q16Dot16 bottomRightSlopeFP = qSafeFloatToQ16Dot16(bottomRightSlope);
const Q16Dot16 invTopLeftSlopeFP = FloatToQ16Dot16(1 / topLeftSlope);
const Q16Dot16 invTopRightSlopeFP = FloatToQ16Dot16(1 / topRightSlope);
const Q16Dot16 invTopLeftSlopeFP = qSafeFloatToQ16Dot16(qSafeDivide(1, topLeftSlope));
const Q16Dot16 invTopRightSlopeFP = qSafeFloatToQ16Dot16(qSafeDivide(1, topRightSlope));
const Q16Dot16 invBottomLeftSlopeFP = FloatToQ16Dot16(1 / bottomLeftSlope);
const Q16Dot16 invBottomRightSlopeFP = FloatToQ16Dot16(1 / bottomRightSlope);
const Q16Dot16 invBottomLeftSlopeFP = qSafeFloatToQ16Dot16(qSafeDivide(1, bottomLeftSlope));
const Q16Dot16 invBottomRightSlopeFP = qSafeFloatToQ16Dot16(qSafeDivide(1, bottomRightSlope));
if (d->antialiased) {
const Q16Dot16 iTopFP = IntToQ16Dot16(int(topBound));
@ -1137,10 +1166,10 @@ void QRasterizer::rasterizeLine(const QPointF &a, const QPointF &b, qreal width,
int iBottom = bottom.y() < 0.5f? -1 : int(bottom.y() - 0.5f);
int iMiddle = qMin(iLeft, iRight);
Q16Dot16 leftIntersectAf = FloatToQ16Dot16(top.x() + 0.5f + (iTop + 0.5f - top.y()) * topLeftSlope);
Q16Dot16 leftIntersectBf = FloatToQ16Dot16(left.x() + 0.5f + (iLeft + 1.5f - left.y()) * bottomLeftSlope);
Q16Dot16 rightIntersectAf = FloatToQ16Dot16(top.x() - 0.5f + (iTop + 0.5f - top.y()) * topRightSlope);
Q16Dot16 rightIntersectBf = FloatToQ16Dot16(right.x() - 0.5f + (iRight + 1.5f - right.y()) * bottomRightSlope);
Q16Dot16 leftIntersectAf = qSafeFloatToQ16Dot16(top.x() + 0.5f + (iTop + 0.5f - top.y()) * topLeftSlope);
Q16Dot16 leftIntersectBf = qSafeFloatToQ16Dot16(left.x() + 0.5f + (iLeft + 1.5f - left.y()) * bottomLeftSlope);
Q16Dot16 rightIntersectAf = qSafeFloatToQ16Dot16(top.x() - 0.5f + (iTop + 0.5f - top.y()) * topRightSlope);
Q16Dot16 rightIntersectBf = qSafeFloatToQ16Dot16(right.x() - 0.5f + (iRight + 1.5f - right.y()) * bottomRightSlope);
int ny;
int y = iTop;