On Apr 30, 2010, at 7:20 AM, Graham Cox wrote: > > On 30/04/2010, at 9:08 PM, steven Hooley wrote: > >>> From your later response it seems like your question is really >> regarding drawing strikethroughs and underlines. If so, the strike >> through and underline are not part of the glyph or font - they are >> just a line drawn from the start point of a range of glyphs to the end >> point of a range of glyphs. You cannot draw them piecemeal, a glyph at >> a time, and expect them to perfectly match up without overlap or >> underlap (apologies for making up a word), as the amount that any 2 >> glyphs overlap is particular to those 2 glyhps. ie. The strikethrough >> of an 'A' followed by a 'V' would need to be a different length than >> that of an 'A' followed by a 'j'. > > > Not that this will tell you anything about what Cocoa does, but when I had to > implement underlines and strikethroughs for text-on-path in DrawKit, I did so > by working a line at a time and knocking out any places where descenders > would hit the line. For text-on-path, drawing a line per glyph looks > absolutely terrible, being straight and not curved, and having gaps where the > character curves away from its neighbour. > > I would imagine that for performance reasons as well as aesthetic, Cocoa > draws whole lines for strikethroughs and underlines as well.
If you zoom your screen by Ctrl-Scrollwheel with TextEdit open, you can see that characters (and their strikethrough/underline) appear to be drawn individually when the character is first inserted (you can see the seams in the strikethrough/underline between characters) but then the line appears to get redrawn all at once about a second later and the seams (mostly) disappear. > I did also discover that relying on the values exactly returned by a font > didn't always give similar results to Cocoa's underline positioning - I never > did quite work out its metrics but arrived at certain fudge factors > empirically that gave almost identical results with most fonts. I was able to get correct metrics for glyphs with ATSUI. But since that is now deprecated I'm rewriting my code to use Cocoa text. I wish I could say that the rewrite was easy, but I'm dying a death of 1000 papercuts. David _______________________________________________ Cocoa-dev mailing list ([email protected]) Please do not post admin requests or moderator comments to the list. Contact the moderators at cocoa-dev-admins(at)lists.apple.com Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/cocoa-dev/archive%40mail-archive.com This email sent to [email protected]
