[ft] putting text in a box

[Dave Calkins]

Given an input text string, a font family, and a pointsize, I'd like to 
draw a filled rectangle background and then draw the text on top of that.

The key is I want the rectangle background to be just large enough to 
contain all the text.

The trouble I'm having is that when I render the text (I'm using 
FreeTypeGL to render in OpenGL), the output position is used to place 
the *baseline* of the text.  I seem to be able to accurately compute the 
overall bounding box of the text, however, I'm having trouble accurately 
figuring out the descender for my string.

And this accuracy is a function of which font I choose.

It seems like the bounding box calculation is always correct.  The 
problem is that the descender I'm querying is for the font face in 
general which I assume accounts for every glyph in the font.

However, if I'm trying to render a particular text string, I only want 
the largest descender for the glyphs in that string.

Any suggestions on computing the descenders for individual glyphs?

I took a look at the glyph metrics from FreeType, but these didn't seem 
to help.  For example, I found a case where "E" seemed to report a 
descender (comparing height and vertBearingY).

Any advice on how to properly place a text string exactly into a rectangle?