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Bug 1185636 - Part 3 - Refactor ArcToBezier so that its implementation can be more easily reused. r=jmuizelaar

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This commit is contained in:
Lee Salzman 2015-07-27 12:12:22 -04:00
parent 2b9080a2e1
commit a6317fea31
1 changed files with 102 additions and 53 deletions
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155
gfx/2d/PathHelpers.h
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@ -13,6 +13,80 @@
namespace mozilla {
namespace gfx {
// Kappa constant for 90-degree angle
const Float kKappaFactor = 0.55191497064665766025f;
// 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.
inline Float ComputeKappaFactor(Float aAngle)
{
return (4.0f / 3.0f) * tanf(aAngle / 4.0f);
}
/**
* Draws a partial arc <= 90 degrees given exact start and end points.
* Assumes that it is continuing from an already specified start point.
*/
template <typename T>
inline void PartialArcToBezier(T* aSink,
const Size& aRadius,
const Point& aStartPoint, const Point& aEndPoint,
const Point& aStartOffset, const Point& aEndOffset,
Float aKappaFactor = kKappaFactor)
{
Float kappaX = aKappaFactor * aRadius.width;
Float kappaY = aKappaFactor * aRadius.height;
Point cp1 =
aStartPoint + Point(-aStartOffset.y * kappaX, aStartOffset.x * kappaY);
Point cp2 =
aEndPoint + Point(aEndOffset.y * kappaX, -aEndOffset.x * kappaY);
aSink->BezierTo(cp1, cp2, aEndPoint);
}
/**
* Draws an acute arc (<= 90 degrees) given exact start and end points.
* Specialized version avoiding kappa calculation.
*/
template <typename T>
inline void AcuteArcToBezier(T* aSink,
const Point& aOrigin, const Size& aRadius,
const Point& aStartPoint, const Point& aEndPoint,
Float aKappaFactor = kKappaFactor)
{
aSink->LineTo(aStartPoint);
if (!aRadius.IsEmpty()) {
Point startOffset = aStartPoint - aOrigin;
startOffset.x /= aRadius.width;
startOffset.y /= aRadius.height;
Point endOffset = aEndPoint - aOrigin;
endOffset.x /= aRadius.width;
endOffset.y /= aRadius.height;
PartialArcToBezier(aSink, aRadius,
aStartPoint, aEndPoint,
startOffset, endOffset,
aKappaFactor);
} else if (aEndPoint != aStartPoint) {
aSink->LineTo(aEndPoint);
}
}
/**
* Draws an acute arc (<= 90 degrees) given exact start and end points.
*/
template <typename T>
inline void AcuteArcToBezier(T* aSink,
const Point& aOrigin, const Size& aRadius,
const Point& aStartPoint, const Point& aEndPoint,
Float aStartAngle, Float aEndAngle)
{
AcuteArcToBezier(aSink, aOrigin, aRadius, aStartPoint, aEndPoint,
ComputeKappaFactor(aEndAngle - aStartAngle));
}
template <typename T>
void ArcToBezier(T* aSink, const Point &aOrigin, const Size &aRadius,
float aStartAngle, float aEndAngle, bool aAntiClockwise)
@ -35,39 +109,30 @@ void ArcToBezier(T* aSink, const Point &aOrigin, const Size &aRadius,
}
Float currentStartAngle = aStartAngle;
Point currentStartPoint(aOrigin.x + cosf(aStartAngle) * aRadius.width,
aOrigin.y + sinf(aStartAngle) * aRadius.height);
Point currentStartOffset(cosf(aStartAngle), sinf(aStartAngle));
Point currentStartPoint(aOrigin.x + currentStartOffset.x * aRadius.width,
aOrigin.y + currentStartOffset.y * 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 =
currentStartAngle + std::min(arcSweepLeft, Float(M_PI / 2.0f)) * sweepDirection;
Point currentEndPoint(aOrigin.x + cosf(currentEndAngle) * aRadius.width,
aOrigin.y + sinf(currentEndAngle) * aRadius.height);
Point currentEndOffset(cosf(currentEndAngle), sinf(currentEndAngle));
Point currentEndPoint(aOrigin.x + currentEndOffset.x * aRadius.width,
aOrigin.y + currentEndOffset.y * 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) * tanf((currentEndAngle - currentStartAngle) / 4.0f);
Float kappaX = kappaFactor * aRadius.width;
Float kappaY = kappaFactor * aRadius.height;
Point tangentStart(-sinf(currentStartAngle), cosf(currentStartAngle));
Point cp1 = currentStartPoint;
cp1 += Point(tangentStart.x * kappaX, tangentStart.y * kappaY);
Point revTangentEnd(sinf(currentEndAngle), -cosf(currentEndAngle));
Point cp2 = currentEndPoint;
cp2 += Point(revTangentEnd.x * kappaX, revTangentEnd.y * kappaY);
aSink->BezierTo(cp1, cp2, currentEndPoint);
PartialArcToBezier(aSink, aRadius,
currentStartPoint, currentEndPoint,
currentStartOffset, currentEndOffset,
ComputeKappaFactor(currentEndAngle - currentStartAngle));
// We guarantee here the current point is the start point of the next
// curve segment.
arcSweepLeft -= Float(M_PI / 2.0f);
currentStartAngle = currentEndAngle;
currentStartOffset = currentEndOffset;
currentStartPoint = currentEndPoint;
}
}
@ -78,42 +143,26 @@ void ArcToBezier(T* aSink, const Point &aOrigin, const Size &aRadius,
template <typename T>
void EllipseToBezier(T* aSink, const Point &aOrigin, const Size &aRadius)
{
Point startPoint(aOrigin.x + aRadius.width,
aOrigin.y);
Point currentStartOffset(1, 0);
Point currentStartPoint(aOrigin.x + aRadius.width, aOrigin.y);
aSink->LineTo(startPoint);
aSink->LineTo(currentStartPoint);
// 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((M_PI/2.0f) / 4.0f);
Float kappaX = kappaFactor * aRadius.width;
Float kappaY = kappaFactor * aRadius.height;
Float cosStartAngle = 1;
Float sinStartAngle = 0;
for (int i = 0; i < 4; i++) {
// We guarantee here the current point is the start point of the next
// curve segment.
Point currentStartPoint(aOrigin.x + cosStartAngle * aRadius.width,
aOrigin.y + sinStartAngle * aRadius.height);
Point currentEndPoint(aOrigin.x + -sinStartAngle * aRadius.width,
aOrigin.y + cosStartAngle * aRadius.height);
Point tangentStart(-sinStartAngle, cosStartAngle);
Point cp1 = currentStartPoint;
cp1 += Point(tangentStart.x * kappaX, tangentStart.y * kappaY);
Point revTangentEnd(cosStartAngle, sinStartAngle);
Point cp2 = currentEndPoint;
cp2 += Point(revTangentEnd.x * kappaX, revTangentEnd.y * kappaY);
aSink->BezierTo(cp1, cp2, currentEndPoint);
// cos(x+pi/2) == -sin(x)
// sin(x+pi/2) == cos(x)
Float tmp = cosStartAngle;
cosStartAngle = -sinStartAngle;
sinStartAngle = tmp;
Point currentEndOffset(-currentStartOffset.y, currentStartOffset.x);
Point currentEndPoint(aOrigin.x + currentEndOffset.x * aRadius.width,
aOrigin.y + currentEndOffset.y * aRadius.height);
PartialArcToBezier(aSink, aRadius,
currentStartPoint, currentEndPoint,
currentStartOffset, currentEndOffset);
// We guarantee here the current point is the start point of the next
// curve segment.
currentStartOffset = currentEndOffset;
currentStartPoint = currentEndPoint;
}
}