From: Ian Hickson <ian@hixie.ch>

Date: Fri, 1 Feb 2008 00:35:06 +0000 (UTC)

Message-ID: <Pine.LNX.4.62.0802010012230.3212@hixie.dreamhostps.com>

Date: Fri, 1 Feb 2008 00:35:06 +0000 (UTC)

Message-ID: <Pine.LNX.4.62.0802010012230.3212@hixie.dreamhostps.com>

On Tue, 3 Jul 2007, Philip Taylor wrote: > > For the 'arc' function: > > What if startAngle = endAngle? Now defined as zero length arc. > What if endAngle > 2? + startAngle? (The endAngle = 2? + startAngle case > isn't interesting since floating-point imprecision means it will never > occur.) According to the spec, nothing special happens. The points are defined as being on the circle, so 3pi = 1pi, as far as where the point is. Clarified, though. > So, for FF/Safari: When startAngle -> endAngle is in the opposite > direction to the (anti)clockwise flag, the two angles are treated modulo > 2? and the arc is drawn between them in the appropriate direction. When > it's the same direction as the (anti)clockwise flag, Safari extends the > path all the way from startAngle to endAngle (going round the whole > circle multiple times if necessary), and Firefox does the same except it > skips all but the first full going-round-the-whole-circle bit (so it > goes round 1 <= n < 2 times, if abs(startAngle-endAngle) > 2?). > > It seems sensible to adopt either Firefox's or Safari's approach (which > differ only in the amount of overdraw). It's probably easier to use > Firefox's, so then Safari would just have to mod the angles a little > before drawing them, because I can't see any other reason to choose one > approach over the other, and I can't see any reason to choose a totally > different approach. Well, having the arc overlap itself seems dumb... :-) > Talking about arcs is confusing when the arc is more than a full > circle and wraps around itself and isn't really a mathematical arc any > more, so I think it's necessary to not define the operation in terms > of arcs. That's another reason not to do this. :-) -- Ian Hickson U+1047E )\._.,--....,'``. fL http://ln.hixie.ch/ U+263A /, _.. \ _\ ;`._ ,. Things that are impossible just take longer. `._.-(,_..'--(,_..'`-.;.'Received on Thursday, 31 January 2008 16:35:06 UTC

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