[cairo] Cairo, pango and Win32.. incorrect font rendering

Peter Clifton pcjc2 at cam.ac.uk
Mon Jan 18 12:51:27 PST 2010

On Mon, 2010-01-18 at 15:36 -0500, Behdad Esfahbod wrote:
> On 01/18/2010 03:28 PM, Peter Clifton wrote:
> > 
> > Is the pango_cairo_context_set_resolution affecting the choice of fonts
> > being offered by the system?
> The resolution set there is used to convert from font size in points to font
> size in cairo user units.  A number in the tens of thousands doesn't make
> sense to me.

No - it isn't obvious where that number has come from. My win32-debug-fu
is pretty low unfortunately - I can't really think how best to
instrument or debug the issue.

Where is the calculation which comes up with the font-size it should ask
Windows for?

> > I still can't figure out why this odd behaviour (which similar might
> > also have been noted on MacOS X) isn't manifesting for me under Wine, my
> > XP box, nor anyone's Linux installs.
> > 
> > It is certainly mis-behaving on at least two people's machines - and I
> > know at least one of those is also XP.
> The bug probably only manifests itself if you use pangocairo with the win32
> font backend, not freetype font backend.

That much I guessed, but the fact that the _same build_ of the software
works on some machines, yet fails on others rather perplexes me. Those
testing who it has failed for claim not to have any other cruft / GTK
apps in their system paths.

Perhaps it is an issue of which fonts are installed? It could, of
course.. be a red-herring, and the manifestation of some memory
corruption - however it does consistently seem to be a problem with text
on the gschem canvas.

My reporters don't seem to have any difference with Cleartype redering
switched on / off.

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