Ellipse tool problem?

[elle]

I think there is a problem with the Ellipse tool in Type 3.2. I'm trying to draw a circle using the Ellipse tool but it doesn't end up very round. This is especially apparent when rotating the circle or rotating something around the circle that's touching the circle.

I'm working in TrueType mode, but the cause of the problem is harder to explain in that mode. If I "Convert to PS Curves", create a new glyph, then draw a 1999 unit diameter circle centered around the origin, I obtain 4 nodes with the following locations and control points:

Loc (1000,0) CP1 (0,551) CP2 (0,-551) West
Loc (0,1000) CP1 (-500,0) CP2 (500,0) North
Loc (-1000,0) CP1 (0,-551) CP2 (0,551) East
Loc (0,-1000) CP1 (500,0) CP2 (-500,0) South

According to:

www.spaceroots.org/documents/ellipse/elliptical-arc.pdf

All of the control vectors should be 552 units long but they aren't.

When I create a circle in regular TrueType mode, the extra nodes appear to be generated by bisecting the segments of the 4 node cubic circle. Since the 4 node cubic circle is itself flawed, the extra nodes do not end up on the radius of an actual circle (even within rounding error). The control vectors are various lengths and sometimes aren't even colinear.

Is there a work-around or fix for this?

Thanks,

elle

[Allan Murray]

Thank you for spotting this, and it will be looked into at the next update. Even though it is actually impossible to create a perfect circle with beziers, the control points should be of equal distance from their respective nodes.

In the mean time, the only work around is to manually adjust the control point positions after creating the circle.

[elle]

Thanks Allan

I tried your suggestion.

After chasing my tail for 30 minutes, I realized that I had to first move all of the derived nodes into position, before adjusting the lengths of the control arms. Since the curves in TrueType mode are only pseudo-cubic, it's only possible to adjust the control arms on every second node independently.

Unfortunately, after making all of the adjustments, the results are still a bit wobbly looking. I don't know whether it's due to rounding issues or something else, but the control arms on the internodes that didn't have their control control arms adjusted, aren't colinear or symmetric.

I would find this problem on the last glyph of a font. I have a pile of glyphs to fix, and I'm not sure that I like the fix. Yes, a total bad hair day. I may just start over and see if I can't get a CFF font to work.

elle

[Allan Murray]

I would suggest that you create the cirlce as a PostScript glyph and make adjustments, because you will have far fewer nodes. Then convert to TrueType.

An update with a fix for this will be within the next few weeks.

[elle]

Thanks once more Allan,

I did some experimenting and decided that PS fonts still seem to be second class citizens in Windows, so a CFF font wasn't an option.

I took your advice and created a couple of glyphs using cubic curves, but I still had some problems after converting the cubics to quadratics. Some of the control points were shifting with respect to others when I manipulated the curves. It must have been something that I was doing, because I couldn't reproduce the problem at will.

While converting the cubics to quadratics, I discovered "TT Points" on the View menu. (Some how I missed that when I read the manual.) But gosh, it's so much easier doing precise work with quadratic B-splines than it is with the pseudo-cubics. I set up a simple spreadsheet to calculate the B-spline control polygon coordinates, and I was able to adjust the control points with that.

[Allan Murray]

This has been corrected in version 3.2.024 (Windows).