Re: Drawing glyph bounding box on rendered text?

[Alex Kerr <alex phonething com>]

Hi August,

Yes I saw that thanks, but the issue was it was hard to discern what the 
actual API calls were, given that I don't do Python and correlate those 
with the C APIs listed in the Pango manual, the Python wrappers seem to 
match up exactly with the C API functions.

Also I'm after bounding boxes around glyphs, which I think the code did 
not seem to do (I can do boxes around runs and lines in C, that seems to 
be easy).

Thanks,
Alex

On 09/05/2011 22:13, august wrote:
> 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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