Re: advancementForGlyph problem
Re: advancementForGlyph problem
- Subject: Re: advancementForGlyph problem
- From: Graham Cox <email@hidden>
- Date: Fri, 30 Apr 2010 23:20:19 +1000
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.
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.
--Graham
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