Elmar Krieger

Born 1974 in Graz, Austria. First games designed and programmed on the Amstrad CPC: Cyborgs (1990), Zap't'Balls (1991), Zap't'Balls - Advanced Edition (1992). The latter brought a contract with Titus Interactive to convert forthcoming PC platform titles to the Amstrad CPC: Super Cauldron (1992) and Prehistorik II (1993). Since at that time games were 100% Assembly code and Nintendo's GameBoy had a CPU rather similar to the Amstrad's Zilog Z80A, a GameBoy version of Prehistorik II followed - called Prehistorik Man (1993). The final game project was StuntRaceFX, a technology demo showing 3D vector graphics and texture mapping on the GameBoy, in the spirit of the SuperNES/SuperFX game (1994). Since then working on www.YASARA.org , a program for research on biomolecules.

Main motivation for writing games was the fun to squeeze unexpected visual effects out of the 8bit CPUs with 64KB of addressable memory and 1 MIPS that ruled these days. Some details follow for those who also liked this kind of Sisyphus jobs:

• The Amstrad CPC could not display hardware sprites. Zap't'Balls disabled the interrupts, put the stack pointer into the video ram and pushed the pixels, using one 'drawing' program per sprite to reach smooth movements at 50 frames per second.

• Super Cauldron had to fit into 64KB and couldn't use page-flipping to avoid flickering. It therefore tracked the position of the cathode ray on screen and cleared/redrew the sprites that were somewhere else.

• Prehistorik II had a special mode for the 'new' Amstrad CPC+ that supported hardware sprites. Unfortunately not enough, so their screen coordinates had to be changed in sync with the cathode ray to make them appear multiple times and add a parallax scrolling front layer. The background layer was created with a drawing program that created an Assembly program that changed the background colour quickly.

• Prehistorik Man was a fight against the limited hardware sprites of the GameBoy: If more than 10 of the maximally 40 sprites (each 8x16 pixels tall) were shown in one pixel line, they simply disappeared. Also sprites did not overlap correctly, the ones with the lower X-coordinate had the higher priority. Prehistorik Man identified sprites likely to cause incorrect graphics and replaced them with software sprites copied into the video ram. It also ported an Amstrad CPC trick to draw big scrolling messages.

• StuntRaceFX changed the colors and the displayed portion of the screen in each pixel line while the GameBoy's 'virtual cathode ray' drew the image. This allowed to compose moving 3D graphics with texture mapping from a single static image combined with hardware sprites. Additional complex vector graphics were precalculated and uncompressed on the fly using an MPEG-like system developed by Mark Piffer.