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Bug 1026596. Add ellipse to bezier helper and use it from SVG. r=bas

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This is faster and more accurate. Specifically, the old code
would produce non-monontic segments which was causing rasterization
differences with skia
This commit is contained in:
Jeff Muizelaar 2014-06-26 16:42:12 -04:00
parent 50ce2cab91
commit 8ae670ea14
2 changed files with 46 additions and 1 deletions
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2
content/svg/content/src/SVGEllipseElement.cpp
View File

@ -125,7 +125,7 @@ SVGEllipseElement::BuildPath()
RefPtr<PathBuilder> pathBuilder = CreatePathBuilder();
ArcToBezier(pathBuilder.get(), Point(x, y), Size(rx, ry), 0, Float(2*M_PI), false);
EllipseToBezier(pathBuilder.get(), Point(x, y), Size(rx, ry));
return pathBuilder->Finish();
}

45
gfx/2d/PathHelpers.h
View File

@ -83,6 +83,51 @@ void ArcToBezier(T* aSink, const Point &aOrigin, const Size &aRadius,
}
}
/* This is basically the ArcToBezier with the parameters for drawing a circle
* inlined which vastly simplifies it and avoids a bunch of transcedental function
* calls which should make it faster. */
template <typename T>
void EllipseToBezier(T* aSink, const Point &aOrigin, const Size &aRadius)
{
Point startPoint(aOrigin.x + aRadius.width,
aOrigin.y);
aSink->LineTo(startPoint);
// 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;
}
}
/**
* Appends a path represending a rounded rectangle to the path being built by
* aPathBuilder.