Stay Frosty for the Atari VCS

Last update: updated links to AtariAge.

On October 29, 2007 I was invited to take part in the 5th annual AtariAge Holiday Cart. The plan for this years cart was to have a number of "mini games" with a slick menu to tie the games together. I contacted my nephew, Justin, for some game ideas and he suggested "You're Frosty collecting stuff" and "You're Rudolf, running away from the other reindeer because they're taunting you". I then started perusing the private Holiday Cart forum and came upon these mockups by Nathan Strum:

Night	Morning
Day	Melting Snowman

One of the challenges with the Holiday Cart is the short turnaround time. My first game, Medieval Mayhem, took about 9 months to complete. Stay Frosty was done in 2.

One of the major differences in programming the VCS vs. modern hardware is the VCS only has 128 bytes of RAM which isn't enough to hold a screen. As such the CPU has to feed TIA, the display chip, with data in real-time to generate the display. This leads to some tradeoffs as there are only 76 cycles of CPU time per scan line. The first tradeoff was the elimination of the carrot nose and the melt trail.

Next to go was 3 fireballs per line. The TIA has hardware to have up to 3 copies of a sprite shown on a scanline, but those copies are linked in what they show, plus they move in lock-step. In order for each fireball to melt by itself the decision was made to "flicker" the sprite so we could have 2 independant fireballs in each zone. Fire naturally flickers, so this was a minor tradeoff.

Once that was resolved the next tradeoff was to slightly narrow the platform area which saved 2 TIA updates per scanline. This tradeoff bought back 18 bytes of some much needed RAM, plus it restored enough CPU time to bring back the melt trail.

Stay Frosty ended up utilizing 12K out of the Holiday Cart's 64K. In that 12K I managed to squeeze in 32 levels. In order to make them all fit I ended up reusing earlier levels later on in the game by adding platform movement.

The levels in the game were designed by myself, Nathan Strum and David Vazquez (who did graphics, animation, label and game manual artwork for Medieval Mayhem). The graphics in Stay Frosty were all done by Nathan Strum.

The screenshots were all generated by Stella, which has a minor flaw in that it doesn't correctly generate the stars hat appear in the night level. As such, I've included a screenshot taken with sdlMESS below. There's also a screenshot of Stay Frosty's select screen from the Holiday Cart, which is also known as Stella's Stocking.

Stars as show in MESS

Game selection screen in Stella's Stocking

Below are some time-lapse screenshots taken during the development of Stay Frosty.

© 2008 Darrell Spice Jr.