🚀 go-pugleaf

J. Joshua needs to know the format of a screen image (DEGAS file) so he can
write a program to isplay DEGAS pictures on VGA.  (I'd like a copy when it's
done).  The following is my understanding of the consensus of the Abacus 
internals book and the Compute Machine Language book.  It differs from the way
I read the Compute VDI book's explanation of the screen, but someone said that
that was wrong anyway, in an earlier discussion.
  Each word (16 bit word) is associated with a particular bitplane.  In 4-color
(medium res) mode,all even numbered words belong to bitplane 0, all odd words
belong to bitplane 1.  In 16 color (low res), every 4th word is bitplane 0, 
etc.  The palette entry is formed by taking 1 bit from each bitplane, in
corresponding positions.  In other words, in medium res, the first point gets
a color determined by the first bit of word 0 and the first bit of word 1.  The
next point gets a color determined by the second bit of word zero and the 
second bit of word 1, etc.
  The header of a DEGAS file is, of course, resolution and palette.
  The Abacus book has pictures that make the situation almost understandable.
The book itself is precious, and understandable as long as you remember that
it's translated from German.
                                        Steve J.