RE: Metapost - text alignment

It would be an excellent idea to implement draw_text_line.
You should then be able to drop draw_text entirely and have 
draw_string call draw_text_line like in diagdkrenderer.

OK, I've taken more of a look. From my reading of DiaRenderer.c, 
draw_text calls draw_text_line for each line. This is where the 
metapost output becomes a problem - if I am rendering $A_{BC}$ in 
metapost, centre aligned, then draw_text subtracts half the length
(text_line_get_alignment_adjustment) and tells 
render_metapost.c (via 
either draw_text_line or draw_string) that it's left aligned at the 
aligned_pos - then metapost renders the text in the wrong position 
because the length correction was not really correct.

Am I reading the code correctly? Should I implement draw_text in 
render_metapost.c so that I get to control the text 
positioning in the 
metapost output? I'm in the "let the export renderer control 
the text 
positioning" camp, if that makes more sense? I note that svg export 
also effectively removes the alignment on export.

Unless DIA goes so far as to have some tight integration with 
a TeX renderer, it will never be able to properly calculate 
the size of $A_{BC}$, which makes proper centering impossible.

MetaPost has two commands for positioning text.   or   draw

The label command will do the left right positioning 
correctly, but it is based on the bounding box, not the 
baseline, so it will not get the vertical positioning correct.

The draw command is based on the left hand end of the baseline.
Vertical positioning will be correct, but unless you can 
calculate text width, you won't get horizontal positioning right.

I am of the opinion that draw is the better way to go.  Most 
text will not have special characters or formulas, so I think 
it is most important to get the common case right (rather than 
none of them).  If a user is using lots of special LaTeX 
formatting, then manually adjusting the horizontal positioning 
isn't that big of a deal.


I see your point, especially about the vertical positioning.

However, I'd suggest that at a minimum you would want to know where the
Metapost output will align to in the horizontal dimension?

For $A_{BC}$, if you wanted it to be aligned to the centre of a box, or
a line on a diagram, you want to know how MetaPost will position it.

My experience of Metapost is short. All the diagrams I have done in
Dia->Metapost have had text which is labeling lines, boxes, etc, and it
seemed to work OK in 0.94 and 0.95-1 (ignoring all the font scaling
problems). I could anchor the text, and know that it would then all
appear around the anchor, or to the left or right, depending on how the
alignment was set.

My thoughts for implementation were to obtain the bounding box from Dia
and then pass this to the Metapost label command. My reading of the code
is that for each string the bounding box is available, as are the size
of the ascent and descent. My understanding was that dia used the
baseline to position the text, and so obtaining the descent for each
string would allow me to calculate where to put the bounding box for
MetaPost. This would make the vertical positioning correct for standard

I've read back throught mail list archive, and read your bug report on
the subject. I will test with a UML class diagram.


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