PTDS (formerly PED81C) - pseudo-native, no C2P chunky screens for AGA

This video shows the Amiga AGA chipset combining 3 full screen 8-bit layers (or playfields, if you prefer) using various 8-bit alpha values.



LAYERS

Background:
* PTDQ system
* 320x200 dots
* max 256 colors

Middleground:
* PTDS system
* 160x200 logical dots, 319x200 physical dots
* max 16 non-transparent colors
* each base color can have an arbitrary 8-bit alpha (actually used: 0 for complete transparency, 128 for dark colors, 255 for bright colors)
* "native" chunky dots (i.e. each byte in the layer buffer corresponds to a dot)
* triple buffer

Foreground:
* PTDQ system
* 320x200 dots
* max 81 non-transparent colors
* each base color can have an arbitrary 8-bit alpha (actually used: 0 for complete transparency, 192 for see-through graphics, 255 for solid graphics)


NOTES

* The color model is RGBW for all the layers, but each layer could use a color model of its own without making any difference performance-wise.
* If the middleground had used PTDQ, its size would have been 320x200 dots and its maximum number of non-transparent colors would have been 81. However, that would have required the PTDQ C2P conversion.
* If the middleground did not use 100% transparent dots, its maximum number of colors would have been 81.
* If the foreground did not use 100% transparent dots, its maximum number of colors would have been 256.
* The display size is actually 319x200 dots to hide the leftmost column of dots, as PTDS requires a 1-dot shift to the right for the even bitplanes.
* The ball is rendered by scaling and flipping in real time a 128x128 chunky bitmap.
* The ball is wiped by means of both CPU and Blitter. The logic that handles the geometry still needs to be refined in order to provide a massive speedup.
* For convenience, the video has been recorded with WinUAE.
* On a stock Amiga 1200, the demo runs at 50 fps except when the ball covers most of the screen (in that case, the frame rate drops proportionally to the size of the ball); the slowdowns will be greatly reduced once the wiping is optimized.
* On an accelerated Amiga, the demo runs at steady 50 fps.
* YouTube's encoding reduced the saturation of colors.


CREDITS

The graphics have been obtained by processing the following pictures:
* boing ball: from OBLIGEMENT / http://obligement.free.fr/gfx4/boingb ... tree_amigacorporation.png
* Earth: from https://cronianverse.fandom.com/wiki/Earth
* plate: from Freepik / https://www.freepik.com/premium-ai-ima ... -background_277147660.htm
* porthole: by winwood1, from Wallpapers.com / https://wallpapers.com/png/round-porth ... 024-zmsra0nm6gp8hvuv.html