Chapter 3 - July 2nd, 2013

Proof of concept

It was time to test the split screen scrolling idea for myself by creating a short routine to gauge the suitabilty of the technique for this project. I knew it could be done, the trick has been used before.


Back in the late 1990's, a game featuring a full 360 degree 3D environment was thought to be impossible on our humble 1.89 Mhz Color Computer 3 when John Kowalski unleashed his Gloom 3D demo to the unsuspecting Color Computer community. It blew everyone's mind.


But could a complete game utilizing a 3D environment be too much to ask?


John and I spoke at length about the algorithym and he helped me understand his 3D technique. I stepped up to the challenge and decided to create a complete game based on John's engine. In 1999, I released my game Gate Crasher utilizing John's Gloom 3D engine (with reduced graphics resolution to obtain the extra speed required for the remaining game elements).


Utilizing John's 3D algorithym, I created Gate Crasher.



John is truly a genius. Locked up in his head are ideas for pushing the boundaries of what the Color Computer was thought to be possible. Some of his ideas appeared in some of his other demos.


One of those demos was a game he had started but never finished called Moon Patrol based on the arcade game of the same name. Here he showed a graphical effect called parallax scrolling which featured several bands on the screen, scrolling independantly and at different speeds.




Split screen and 1 byte scrolling made it's debut on the CoCo in John Kowalski's unfinished game Moon Patrol.



Some of these effects have been done before on Commodore and Atari systems but never on the Color Computer utilizing hardware tricks. While I understood how it was done on these other systems, it was John who made it clear to me how a similar effect could be done on the Color Computer 3.


Now, over 10 years later, I have finally commited to putting those ideas together and build a game from them. Below is a screenshot of the test routine I used to try out the split screen scrolling technique. Later I will try out the 1 byte scroll.





Here, I first filled the screen with a striped pattern to make it easier to see what areas of the screen were being moved and how smoothly. The very top of the screen and bottom of the screen was held stationary while 2 bands in between were made to scroll in opposite directions. The rest is just a matter of synchronising to the horizontal interrupts and changing the Horizontal Offset register appropriately at the right times.


You can see the results for yourself. Download the  disk image here:   SCROLL TEST



Now we have proof-of-concept and it prepares me for the next stage of development.





Copyright 2013 by Nickolas Marentes