Re: Cocoa and PICT
Re: Cocoa and PICT
- Subject: Re: Cocoa and PICT
- From: Alastair Houghton <email@hidden>
- Date: Fri, 10 Aug 2007 23:35:00 +0100
On 10 Aug 2007, at 22:57, Scott Thompson wrote:
On Aug 10, 2007, at 4:25 PM, Alastair Houghton wrote:
On 10 Aug 2007, at 14:51, glenn andreas wrote:
There's even support for smoothing polygons using picture
comments, which might be handy for simulating bezier paths.
Quickdraw pic comment based smooth polygons are cubics, and
bezier paths are quadratic curves, and converting from one to the
other is non-trivial (for any sort of decent quality).
I think you got that the wrong way round. QuickDraw PolySmooth
picture comment uses quadratic curves; NSBezierPath provides a
cubic primitive. (Plainly you knew what you meant, since
converting quadratic curves to cubics is easy... it's the other
way that requires piecewise approximation.)
Kind regards,
Alastair.
Well, if we're going to pick on Glenn :-)
:-) For the record, I just wanted the list archives to be clear. I
know Glenn meant to write it the right way around.
It's also the case that the cubic and quadratic curves are both
Bezier curves. So the more accurate statement might be that
"QuickDraw's pic comment based smooth polygons are quadratic bezier
curves" while "NSBezierPath are based on cubic bezier curves".
Sure.
It's interesting to note, however, that the Core Graphics library
that lies underneath NSBezierPath has direct support for quadratic
bezier curves. See CGContextAddQuadCurveToPoint
Yes, not surprisingly given that Quartz can be used to render text,
and TrueType fonts use quadratic Béziers.
In Tiger It's not too hard to put some Quartz 2D calls in the midst
of your NSBezierPath-and-friends drawing so if you REALLY wanted to
parse the PICT comments and draw quadratic curves, you could
probably do it without too much trouble.
I think the point was that the conversion was going the other way...
i.e. taking something Quartz-ish (like an NSBezierPath or a CGPath)
and turning it into a PICT description. Which, of course, requires
approximation.
Kind regards,
Alastair.
--
http://alastairs-place.net
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