Re: GR_UnixPangoGraphics::_scaleCharacterMetrics unit confusion

(Without commenting on your analysis, as I *suck* at font rendering
issues)

Thanks a lot John, for taking the time to investigate this. It is very
much appreciated.

Cheers,
  Marc

On Tue, 2009-02-03 at 02:58 -0500, John Wehle wrote:
> >> 1) _tduX is looks like it works in layout units which appears
> >> to be 1440. How can it take something in pango units when
> >> it expects layout units?
> >>
> >
> > This absolutely correct. _tduX converts a layout unit to a device unit.
>
> Which still leaves the oddity that _scaleCharacterMetrics is feeding
> it pango units * not * layout units so my question still stands.
>
> Further browsing of the code reveals:
>
> m_pGlyphs is filled in by pango_shape using a font loaded using
> the layout context so the geometry is layout pixels pango units.
>
> m_pScaledGlyphs is used by pango_xft_render using a font loaded
> using the output device context so the geometry is device pixels
> pango units.
>
> which is why _scaleCharacterMetrics can get away with using tdu.
>
> Now there does seem to be the flawed belief that the results from
> pango_shape can be safely used with pango_xft_render when a different
> font (i.e. pango_context_load_font) is being used with each function
> which can cause gibberish to be displayed. I've logged an analysis
> of the gibberish problem in bugzilla.abiword.com as bug id 11946.
>
> > Could you tell me which version of abiword, and gtk you are using?
>
> abiword 2.6.6
>
> glib-2.18.4
> pango-1.22.4 (also tried pango-1.20.5)
> gtk+-2.12.12
>
> X11R7.3
>
> > All this works perfectly on current linux distros.
>
> That's part of what makes this interesting, though it certainly
> doesn't eliminate the possibility of a bug in the code.
>
> > I wonder if perhaps you're regularly hitting an irregular code
> > pathway? To tell, look at the method:
> >
> > GR_UnixPangoGraphics::renderChars(GR_RenderInfo & ri)
>
> DEBUG: GR_UnixPangoGraphics::setFont: times new roman
> DEBUG: GR_UnixPangoGraphics::renderChars length 3
> DEBUG: Pango renderChars: xoff 1768 yoff 1768
> DEBUG: Doing XFT Render now.
>
> > If you're hitting the preferred code pathway, you should see that
> > debug message on every character draw.
>
> I do.
>
> I've logged an analysis of the smudging problem in bugzilla.gnome.org
> as bug id 570182.
>
> -- John
> -------------------------------------------------------------------------
> | Feith Systems | Voice: 1-215-646-8000 | Email: john@feith.com |
> | John Wehle | Fax: 1-215-540-5495 | |
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>
Received on Tue Feb 3 23:31:01 2009