[Coco] Next arcade port to CoCo 3

John Kowalski sock at axess.com
Mon Apr 9 23:03:13 EDT 2007

Jim wrote:
>Mark McDougall <msmcdoug at iinet.net.au> wrote:
>The biggest problem I see is scrolling large areas of the screen as the 
>player moves up and down in the elevator - something done in hardware on the 
>machine itself.
>Would the horizontal scrolling of 'Mappy" likewise be out of reach?

The scrolling in Elevator Action can be visualized to be similar to looking
at the spinning wheels in a slot machine.  The video hardware is able to
split the screen into vertical stripes that can each be slid up or down

A good visible example of this is in the game's title screen, where each
letter of the word ELEVATOR is seen moving up and down indepenently.  The
game isn't actually drawing anything, nor are they sprites - they're
actually part of the background.   The CoCo simply does not have any
hardware effect equivalent to this.  The fact that the game *also* has
non-scrolling areas at the top and bottom of the screen just complicates the
problem even further.

Mappy, on the other hand, scrolls horizontally.  The CoCo 3 does have
horizontal scrolling in hardware, although not as smooth as the arcade game's.
A bit more tricky is that Mappy *also* has non-scrolling portions of the
screen at the top and bottom, but in Mappy's case, some creative programming
to update the GIME's horizontal scroll registers at exactly the right times
during the video raster could simulate the same effect that Mappy does hardware.

So, Mappy - Tricky but possible.

Elevator Action - No. (Unless a horrible, horrible frame rate is acceptable.)

                                         John Kowalski (Sock Master)

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