> 
> On 22 Sep 2012, at 01:33, Graham Cox <graham....@bigpond.com> wrote:


> You might investigate an alternative (and much easier) solution.
> 
> NSLayoutManager adopts the NSGlyphStorage protocol. That protocol declares a 
> method, -layoutOptions, and one of the flags it can return is 
> NSShowInvisibleGlyphs. Simply returning that flag may be all you need to do.
> 
> In fact I think this is set for you when you call 
> -setShowsInvisibleCharacters:YES
> 
> I guess the difference is that it's all or nothing, which might be not the 
> desired result.
Works just for space characters, not other whitespace characters.
Plus there is no attribute control so it isn't possible to colourise the 
invisible character glyph as I currently do.
> 
> 
> 
> Another approach is to override 
> -showCGGlyphs:positions:count:font:matrix:attributes:inContext: which is the 
> primitive drawing method. All of the positioning and context flippedness has 
> been handled by this point, so you can usually just go ahead and draw the 
> characters. Inserting some other glyph at this point for the tab should be 
> straightforward.
> 
Good idea.
I will investigate this one.
However Kyle's idea of modifying the glyph stream may be better.
It means that there is no second guessing required when it comes to positioning 
the substituted glyph.
However, I don't know as yet whether I will be able to specify the required 
font colour. We shall see.

Thanks for the advice Graham.

Regards

Jonathan Mitchell
Mugginsoft LLP



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