[dvipng] incorrect depth/height in dvipng

[Nilton Volpato]

Hi Jan-Åke,

I was trying to use depth/height options with dvipng. I thought that
its output should follow this idea.

## |
# |
#### ### | height
# # # # |
# # # # |
### #### |
# | depth
### |

However the results does not seem to match this model. Look at this example:

\documentclass[10pt,notitlepage]{article}
\usepackage{preview}
\usepackage[margin=0.95in]{geometry}
\pagestyle{empty}
\begin{document}
\noindent \rule[-0.5cm]{2cm}{2cm} foobar
\end{document}

$ latex dvipng_test.tex
[...]
Output written on dvipng_test.dvi (1 page, 228 bytes).
Transcript written on dvipng_test.log.

$ dvipng --height --depth dvipng_test.dvi
This is dvipng 1.9 Copyright 2002-2006 Jan-Ake Larsson
[1 depth=74 height=5]

$ identify dvipng_test1.png
dvipng_test1.png PNG 122x79 122x79+0+0 PseudoClass 15c 8-bit 358b

The output image is 79 pixels high, so, because of
\rule[-0.5cm]{2cm}{2cm}, the depth reported by dvipng should be 79/4
~= 20 and the height should be 3*79/4 ~= 59. But dvipng output doesn't
make sense, except that depth+height=79.

Is dvipng wrong? Is it reporting depth/height following another model?
Or something else?

Thanks,
-- Nilton