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Bug 1187210 - limit ArcToBezier sweeps while taking care of floating-point inaccuracy. r=eihrul

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This commit is contained in:
Lee Salzman 2015-07-25 02:45:02 -04:00
parent 040bd5a1d4
commit cc40b36469
1 changed files with 21 additions and 33 deletions
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54
gfx/2d/PathHelpers.h
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@ -17,63 +17,50 @@ template <typename T>
void ArcToBezier(T* aSink, const Point &aOrigin, const Size &aRadius,
float aStartAngle, float aEndAngle, bool aAntiClockwise)
{
Point startPoint(aOrigin.x + cosf(aStartAngle) * aRadius.width,
aOrigin.y + sinf(aStartAngle) * aRadius.height);
Float sweepDirection = aAntiClockwise ? -1.0f : 1.0f;
aSink->LineTo(startPoint);
// Calculate the total arc we're going to sweep.
Float arcSweepLeft = (aEndAngle - aStartAngle) * sweepDirection;
// Clockwise we always sweep from the smaller to the larger angle, ccw
// it's vice versa.
if (!aAntiClockwise && (aEndAngle < aStartAngle)) {
Float correction = Float(ceil((aStartAngle - aEndAngle) / (2.0f * M_PI)));
aEndAngle += float(correction * 2.0f * M_PI);
} else if (aAntiClockwise && (aStartAngle < aEndAngle)) {
Float correction = (Float)ceil((aEndAngle - aStartAngle) / (2.0f * M_PI));
aStartAngle += float(correction * 2.0f * M_PI);
if (arcSweepLeft < 0) {
// Rerverse sweep is modulo'd into range rather than clamped.
arcSweepLeft = Float(2.0f * M_PI) + fmodf(arcSweepLeft, Float(2.0f * M_PI));
// Recalculate the start angle to land closer to end angle.
aStartAngle = aEndAngle - arcSweepLeft * sweepDirection;
} else if (arcSweepLeft > Float(2.0f * M_PI)) {
// Sweeping more than 2 * pi is a full circle.
arcSweepLeft = Float(2.0f * M_PI);
}
// Sweeping more than 2 * pi is a full circle.
if (!aAntiClockwise && (aEndAngle - aStartAngle > 2 * M_PI)) {
aEndAngle = float(aStartAngle + 2.0f * M_PI);
} else if (aAntiClockwise && (aStartAngle - aEndAngle > 2.0f * M_PI)) {
aEndAngle = float(aStartAngle - 2.0f * M_PI);
}
// Calculate the total arc we're going to sweep.
Float arcSweepLeft = fabs(aEndAngle - aStartAngle);
Float sweepDirection = aAntiClockwise ? -1.0f : 1.0f;
Float currentStartAngle = aStartAngle;
Point currentStartPoint(aOrigin.x + cosf(aStartAngle) * aRadius.width,
aOrigin.y + sinf(aStartAngle) * aRadius.height);
aSink->LineTo(currentStartPoint);
while (arcSweepLeft > 0) {
// We guarantee here the current point is the start point of the next
// curve segment.
Float currentEndAngle;
Float currentEndAngle =
currentStartAngle + std::min(arcSweepLeft, Float(M_PI / 2.0f)) * sweepDirection;
if (arcSweepLeft > M_PI / 2.0f) {
currentEndAngle = Float(currentStartAngle + M_PI / 2.0f * sweepDirection);
} else {
currentEndAngle = currentStartAngle + arcSweepLeft * sweepDirection;
}
Point currentStartPoint(aOrigin.x + cosf(currentStartAngle) * aRadius.width,
aOrigin.y + sinf(currentStartAngle) * aRadius.height);
Point currentEndPoint(aOrigin.x + cosf(currentEndAngle) * aRadius.width,
aOrigin.y + sinf(currentEndAngle) * aRadius.height);
// Calculate kappa constant for partial curve. The sign of angle in the
// tangent will actually ensure this is negative for a counter clockwise
// sweep, so changing signs later isn't needed.
Float kappaFactor = (4.0f / 3.0f) * tan((currentEndAngle - currentStartAngle) / 4.0f);
Float kappaFactor = (4.0f / 3.0f) * tanf((currentEndAngle - currentStartAngle) / 4.0f);
Float kappaX = kappaFactor * aRadius.width;
Float kappaY = kappaFactor * aRadius.height;
Point tangentStart(-sin(currentStartAngle), cos(currentStartAngle));
Point tangentStart(-sinf(currentStartAngle), cosf(currentStartAngle));
Point cp1 = currentStartPoint;
cp1 += Point(tangentStart.x * kappaX, tangentStart.y * kappaY);
Point revTangentEnd(sin(currentEndAngle), -cos(currentEndAngle));
Point revTangentEnd(sinf(currentEndAngle), -cosf(currentEndAngle));
Point cp2 = currentEndPoint;
cp2 += Point(revTangentEnd.x * kappaX, revTangentEnd.y * kappaY);
@ -81,6 +68,7 @@ void ArcToBezier(T* aSink, const Point &aOrigin, const Size &aRadius,
arcSweepLeft -= Float(M_PI / 2.0f);
currentStartAngle = currentEndAngle;
currentStartPoint = currentEndPoint;
}
}