I know it's a faq, but: Pixmaps

[katre <katre ruf rice edu>]

I am aware that this question gets asked rather frequently, but I looked at
the mailing-list archives, and they don't go past January, so I guess I'll ask
again.

I have a widget, that shows stuff in a window.  The stuff is kept by the
widget in a backing_pixmap, which gets drawn to the window during expose.
All right, all good, it works well.  For reasons too complex to go into, I
now need to change to having _two_ backing_pixmaps, one with permanent data,
and one with temporary data.  However, i cannot get the second to draw
properly.  No matter what I do, when the second pixmap gets drawn to the
window, the entire window goes black.  I have tried initializing the second
pixmap by drawing a rectangle that fills the entire pixmap with several
colors, including white and "none", (which I don't know for sure would work,
but it didn't crash).  However, nothing seems to work.  So:
1) How do I make a pixmap with a transparent background?
2) What do the fore and background colors in the gc mean when you're drawing
pixmaps, anyway?
and 3) Help!

katre