🚀 go-pugleaf

I am pleased to find out that buffered graphics are possible with GEM (in
fact even with the subset of GEM available from OSS Personal Pascal).

The XBIOS recognizes two screen bitmaps, the logical buffer and the physical 
buffer.

All GEM graphics output goes to the logical buffer.  The physical buffer
is the bitmap which is visible on the screen.  When the logical and
physical buffers are the same (i.e. have the same address) graphics output
is immediately visible on the screen.  As graphics commands are given one
can watch the screen change.  By default, the physical and logical screen
buffers are the same.

However, by using a different logical buffer one can send graphics
output to the logical buffer without it being visible on the display
screen.  Later, the contents of the logical buffer can be "blasted" to
the display screen.

This technique is useful when one needs to make a complex drawing and have it 
blasted to the screen after it's been completely formed, rather than 
have the user watch as it is slowly drawn.  Even if it still takes the same
amount of time to draw the image, it will tend to appear faster to a user.

Finally, I could furnish examples in OSS Personal Pascal if there is any
interest.




Eric Terrell (att!druhi!terrell)