Re: Drawing glyph bounding box on rendered text?

[august <august alien mur at>]

Behdad posted a python application that draws lines around clusters,
runs, and lines:

	http://mail.gnome.org/archives/gtk-i18n-list/2011-April/msg00007.html

Maybe you haven't seen that yet and can help.

best -august.

> Hi all,
> 
> I'm trying to accurately draw a rectangle around each glyph (not
> character) in rendered text. I'm very close but things aren't quite
> lining up correctly. I've attached an image showing this, but if the
> mailing list filters it, you can also see it here:
> http://www.phonething.com/test.png
> Green box shows line extents, red boxes should show bounding box for
> each glyph.
> 
> As you can see, widths and X starting positions of the boxes are off
> slightly. (So is height, but I suppose I could lock that to the
> bottom of the line extents?)
> 
> Relevant code that drew that is:
> 
> double pango_to_ink = (1.0 / ((double) PANGO_SCALE)); // utility
> 
> [ create surface, context, layout, then do pango_layout_set_text() ]
> 
> [ for each line in layout use pango_layout_iter_get_line() : ]
> 
> pango_layout_iter_get_line_extents(pIter, &line_r, NULL);
> pangolineX = pango_to_ink * ((double) line_r.x);  // start position
> of this line of the layout
> pangolineY = pango_to_ink * ((double) line_r.y);
> 
> [ get each run in current line: ]
> 
> for (i = 0; i < pRun->glyphs->num_glyphs; i++) // loop through
> glyphs in current run
>      {
> 
>      pango_font_get_glyph_extents(font, glyphID, NULL, &glyphbox);
> // Just to get glyph height as it's not in the geometry
> 
>      glyphX = pangolineX + pango_to_ink * ((double)
> pRun->glyphs->glyphs[i].geometry.x_offset);
>      glyphY = pangolineY + pango_to_ink * ((double)
> pRun->glyphs->glyphs[i].geometry.y_offset);
>      glyphW = pango_to_ink * ((double)
> pRun->glyphs->glyphs[i].geometry.width);
>      glyphH = pango_to_ink * ((double) glyphbox.height);
> 
>       cairo_rectangle(context, glyphX, glyphY, glyphW, glyphH - glyphY);
>       cairo_stroke(context);
> 
>       }
> ....
> 
> Where am I going wrong in getting the glyph bounding boxes
> accurately? (this needs to also work for Indic, Hebrew, Arabic,
> Chinese and so on)
> It doesn't matter if the box has empty space, i.e. incorporates the
> distance between glyphs, though knowing the actual glyph bounding
> box AND the space separating it from the next glyph
> would be ideal.
> 
> Thanks and regards,
> Alex
> 


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