EndpointToCenterArcParams bug

[thenewvu]

Hello,

This article led me here.

I found a bug in:

fuselibs/Source/Fuse.Drawing.Surface/SurfaceUtil.uno

Lines 138 to 148 in 8fb40bb

	//(F.6.5.6)
	double delta = svgAngle(
	(x1p - cxp)/rX, (y1p - cyp)/rY,
	(-x1p - cxp)/rX, (-y1p-cyp)/rY);
	delta = Math.Mod(delta, Math.PIf * 2 );
	if (!flagS)
	delta -= 2 * Math.PIf;
	r_ = float2((float)rX,(float)rY);
	c = float2((float)cx,(float)cy);
	angles = float2((float)theta, (float)delta);

According to the spec (the bold text):

where Δθ is fixed in the range −360° < Δθ < 360° such that:

if fS = 0, then Δθ < 0,

else if fS = 1, then Δθ > 0.

In other words, if fS = 0 and the right side of (eq. 5.6) is greater than 0, then subtract 360°, whereas if fS = 1 and the right side of (eq. 5.6) is less than 0, then add 360°. In all other cases leave it as is.

... the code should be:

    //(F.6.5.6)
    double delta = svgAngle(
        (x1p - cxp)/rX, (y1p - cyp)/rY,
        (-x1p - cxp)/rX, (-y1p-cyp)/rY);
    delta = Math.Mod(delta, Math.PIf * 2 );
    if (flagS && delta < 0)
    {
        delta += 2 * Math.PIf;
    }
    else if (!flagS && delta > 0)
    {
        delta -= 2 * Math.PIf;
    }