Software rendering

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Software rendering is only possible without additionnal hardware on CD systems.

As the sprites and fix DRAM is used by the GPU during display, updating of the tiles can only be done during vblank.

The BIOSF_UPLOAD System ROM call can be used to do a DMA or loop based copy of pre-rendered pixel data from RAM to DRAM. Of course, the data needs to be in the correct format for it to be displayed properly:

Demo

Does NOT work on the real NeoGeo CD, screen keeps flashing. Perhaps DMA isn't possible when the video output is enabled

Nebula screenshot

File:Softrender.zip

Plots pixel with varying colors on the fix layer. Source code for AS and ready to burn ISO image included.