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Comment by Scali | Hacker News Reader

Well, I would argue that a 'conventional' video codec would not work nearly as well on a stock Amiga 500 as this polygon approach does. The closest thing to full-motion video on the platform was probably what they used on the CDTV (same hardware as an Amiga 500, but with CD-ROM). It used the CDXL format: https://en.wikipedia.org/wiki/CDXL.

In short, you got 160x100 video at 12 fps. It was uncompressed data, because the system was too slow to decompress in realtime. So the Amiga really wasn't powerful enough for 'conventional' codecs to begin with. Especially 9 Fingers gets pretty detailed video at the full resolution and certainly more than 12 fps. And the whole thing fits on just two floppies, so the storage is quite efficient as well. Imagine what you could do with a CD-ROM.

The successor to the CDTV, the CD32, got a hardware MPEG decoder, despite having a much faster CPU and chipset than the original Amiga the CDTV was based on.

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I had a CDTV and a CD32, but I never knew the details about CDXL format, thank you! I just checked and it looks like ffmpeg supports it, bless. It looks like the simplest possible video encoding format you could imagine.

Yes, the reason I was doing it like that on the PC was for the same reason you mention -- using polygons probably is faster because you cut out a lot of math and branches (as long as the polys are large enough) and just drop down to blitting huge swathes of solid color into the frame buffer.

On a PC it is different, because you need to render the polygons in software. On an Amiga you basically draw lines into each bitplane, and then do a single area fill at the end, all with the blitter. The area fill won't have to be stored, as this is done for each frame. Which means you only need to store the lines, and those can be stored directly as preprocessed register values for the blitter. So you can basically just stream the data directly from floppy and fire it off into the blitter.

But as I say, on early PCs you couldn't draw ANYTHING quickly into video memory. Which is also why for the 8088 MPH demo I developed a polygon renderer that calculated the differences with the previous frame, and then only drew that. This allowed a much higher framerate than clearing the stream and redrawing all polys. Similar to how the XDC encoder here encodes the differences.

On the Amiga the CPU isn't fast enough to draw entire screens either, but it has the chipset with the blitter, DMA transfers and whatnot to help it.

That is an interesting difference with the 8088+CGA platform by the way. The Amiga has no problem displaying entire screens of uncompressed data. CGA however is so bandwidth-limited that you simply can't update an entire screen at acceptable framerates, so the lossy compression that is used with XDC is a requirement to improve the framerate to FMV-like levels, it is not primarily required for data reduction on disk.

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