🚀 go-pugleaf

I am trying to use ScrollVPort to do horizontal and vertical scrolling
of a 320x200x4 screen over a 640x400x4 display area.  I have two problems.

One, from watching the Performance Monitor (PM, thanks Dale Luck!), I
have observed that about 50% of the available CPU cycles are consumed
by heavy (x and/or y scroll changes every 16.7 ms) horizontal and vertical
scrolling.  I assume that most of this overhead is ScrollVPort's
twiddling the copper lists.

Two, there is an occasional glitch where, apparently, my pixels that select
color register zero show as white instead of what they should be, black.

The obvious questions are:  1)  Is there a way to scroll around the VPort
with less overhead?  I have Workbench going as well as a couple of other
screens defined.  2) Is there a way to get it to not glitch occasionally?
I notice in ScrollVPort's "BUGS" entry that it's not fast enough to
avoid some visible hashing of display.  Is this what's happening and
again, can I get around it?

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