The docs for slideshow's (dc ...) call didn't mention the use of the 'a' and 'd' arguments. I inferred based on the following docs that these referred to ascent and descent, and assumed based on the following docs that these were added to the height passed to the procedure. Let me know if I should/shouldn't push the commit below:
John
oiseau:~/plt/collects/scribblings/slideshow clements$ git show 72edb8c
commit 72edb8c861ecb5ccfb90ade8d83ae86a6289bc13
Author: John Clements <cleme...@racket-lang.org>
Date: Sat Jan 28 15:11:18 2012 -0500
added docs for a&d args of slideshow's dc procedure
diff --git a/collects/scribblings/slideshow/picts.scrbl
b/collects/scribblings/slideshow/picts.scrbl
index f3ded67..726c361 100644
--- a/collects/scribblings/slideshow/picts.scrbl
+++ b/collects/scribblings/slideshow/picts.scrbl
@@ -131,7 +131,14 @@ When the rendering procedure is called, the current pen
and brush will
be solid and in the pict's color (and linewidth), and the scale and
offset of the dc will be set. The text mode will be transparent, but
the font and text colors are not guaranteed to be anything in
-particular.}
+particular.
+
+In the three-argument
+case, the ascent and descent are @math{0} for the resulting pict's
+bounding box; in the five-argument case, the height is computed by
+adding the given ascent and descent.
+
+}
@defproc*[([(blank [size real? 0]) pict?]
[(blank [w real?] [h real?]) pict?]
oiseau:~/plt/collects/scribblings/slideshow clements$
smime.p7s
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