Re: GR_UnixPangoGraphics::_scaleCharacterMetrics unit confusion

On Sat, Jan 31, 2009 at 5:59 AM, John Wehle <john@feith.com> wrote:
>> Another possibility for your problem is that m_iDeviceResolution is
>> not set correctly.
>
> It looks reasonable.
>
>> In all my builds I always see a device resolution of 96.
>
> The existing debug statements said:
>
> DEBUG: GR_UnixPangoGraphics::graphicsAllocator
> DEBUG: Initializing UnixPangoGraphics 8954000
> DEBUG: cursor set to 1 gdk 68
> DEBUG: @@@@@@@@@@@@@ retrieved DPI 96 @@@@@@@@@@@@@@@@@
>
> And the statement I added to tdu said:
>
> Zoom 114 DeviceRes 96 Res 1440
>

OK this is all fine

<snip>

>>> 1) I believe RI.m_pGlyphs->glyphs[i].geometry.width is PangoGlyphUnit,
>>> not layout units.
>>
>> It starts out that way but it must end up in device units, ie the
>> actual pixel position on the screen.
>
> Okay I'm even more confused. What I see in the code is:
>
> pango_shape fills out m_pGlyphs based on the chosen font
>
> _scaleCharacterMetrics is intended to fill m_pScaledGlyphs
> based on m_pGlyphs and the current zoom
>
> m_pScaledGlyphs is passed to pango_xft_render to draw the
> actual glyphs
>
> My pango documentation indicates that pango_shape fills in
> glyphs with geometry information based on PANGO_SCALE (1024)
> of a device unit. The documentation also indicates that
> pango_xft_render expects the geometry of the glyphs to be
> based on PANGO_SCALE (1024) of a device unit (i.e. the same
> units as pango_shape).
>
> 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.

> 2) What am I missing in the pango documentation regarding the
> units used by the glyph parameter to pango_xft_render?
>
> I do see that the x and y offsets passed to pango_xft_render for
> where to start are in pixels, however that's separate from the
> glyph information.
>
>> The _tduX() method does what you want but in addition takes into
>> account rounding unit adjustments when doing a horizontal scroll, (in
>> case the width of the page is bigger that your frame).
>
> I understand this when dealing with the x offset of the glyph. I don't
> understand how anything regarding the scroll affects the glyph width.
> Can you give me an example?
>

Not easily, but this a red-herring in any case. The effect of _tduX is
make sure all the text lines up to within the nearest
pixel. You describe a situation where something is fundamentally broken.

Could you tell me which version of abiword, and gtk you are using? All
this works perfectly on current linux distros.

I wonder if perhaps you're regularly hitting an irregular code
pathway? To tell, look at the method:

 GR_UnixPangoGraphics::renderChars(GR_RenderInfo & ri)

Change:

        xxx_UT_DEBUGMSG(("Pango renderChars: xoff %d yoff %d\n",
                                         RI.m_xoff, RI.m_yoff));
        to

        UT_DEBUGMSG(("Pango renderChars: xoff %d yoff %d\n",
                                         RI.m_xoff, RI.m_yoff));
        
If you're hitting the preferred code pathway, you should see that
debug message on every character draw.

If you're hitting the other pathway, you'll see the debugmsg:

                UT_DEBUGMSG(("Drawing glyph subset from %d to %d (offsets %d, %d)\n",
                                         iGlyphsStart, iGlyphsEnd,
                                         iOffsetStart, iOffsetEnd));

Which do you see?

Thanks!

Martin

> -- John
> -------------------------------------------------------------------------
> | Feith Systems | Voice: 1-215-646-8000 | Email: john@feith.com |
> | John Wehle | Fax: 1-215-540-5495 | |
> -------------------------------------------------------------------------
>
>
Received on Sat Jan 31 02:26:01 2009