[cairo] Font interface problem
dmon at xs4all.nl
Tue Mar 9 16:45:44 PST 2004
> -----Original Message-----
> From: cairo-admin at cairographics.org
> [mailto:cairo-admin at cairographics.org] On Behalf Of Bill Spitzak
> Sent: dinsdag 9 maart 2004 23:43
> To: Maarten Breddels; 'Carl Worth'
> Cc: cairo at cairographics.org
> Subject: Re: [cairo] Font interface problem
> On Tuesday 09 March 2004 01:21 pm, Maarten Breddels wrote:
> > And, do you agree that fonts drawn with:
> > cairo_scale(2,2)
> > cairo_scale_font(2)
> > Are '4' (whatever units) high, but it's a font of height 2, linearly
> > scaled 2 times in x in y.
> > While:
> > cairo_scale(1,1)
> > cairo_scale_font(4)
> > Is a font of height 4, and isn't scaled.
> > It matters(not that much though) because ttf(truetype fonts) are
> > transformed (not necessarily linear) at different sizes to keep them
> > readable. Currently they are both drawn as 4 units high,
> not scaled in
> > any way.
> I think fonts should be drawn identically for a given
> transform, no matter
> what portion of that transform is in the CTM and what part is
> in the font
Are you sure, this would make things like zooming impossible. I know I'm
splitting hairs here, and it's convenient if it works like you are
describing here, but it is limiting cairo. I don't wanna make a big deal
out if, but I might be worth discussing about.
> There should be seperate arguments to the font selector
> interface to indicate
> "draw as though you are N points tall". This is much more
> similar to setting
> the weight or other attributes of the font than to scaling.
> There could be a "simple" font choosing interface that takes
> a "size" and
> sets the font matrix to that size and also sets the "draw as
> though you are N
> points tall" to the same value (or that value*96/72 to turn
> Cairo units into
> points on the assumption that the CTM is the default matrix).
> But internally
> this should be seperated as fast as possible.
Yes, good idea, sth like cairo_set_font_size(12), and you should get 12
point high font, only depending on your 'pixels_per_inch'. It could also
look at the CTM to make a matching font matrix.
> PLEASE don't make the mistake of specifying the size of the
> font in "points"
> or any unit other than the CTM units. This makes it
> impossible to produce
> predictable graphics unless I go in and retrieve exactly how
> you map pionts
> to font matricies and then calculate the inverse, a total
> waste of time on
> everybody's part. If I want to take advantage of a font
> renderer that draws
> differently depending on the points, you should use a fixed
> and predictable
> way of turning the size into "points" (such as assumming that
> the CTM is
> 1/96), or let me independently specify this "points" value,
> since I know the
> "point size" much better than Cairo does (I may be trying to
> actually draw a
> reduced-size image of the paper, for instance).
Ofcourse, when the font matrix scales 40x40, and CTM is set to the
identity matrix, the font should be 40 pixels high on a raster display,
instead of 40 'points', whatever that size may be.
Btw, cairo_gstate_t has a pixels_per_inch member, so that will define
the size of the font(pixelheight=pixels_per_inch*pointsize/72).
Greetings from .nl, Maarten
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