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Old 09 May 2017, 17:08   #25
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Join Date: Dec 2015
Location: Poland
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Originally Posted by pandy71 View Post
DMA limitations can be (IMHO) partially overworked by using less bitplanes and drive BPLxDAT by Copper/CPU (useful for 4 bpl lowres to efficiently double number of color registers, perhaps can be useful also for 2 and 3 bpl hires - this probably will require software like this on Atari ST and carefully cycled color LUT updates).

PNG with max compression (without optimization) - 12 bit per pixel (over 600 colors, OCS bitwise - 4 bit per component) vs 16 color (4 bit per pixel).
ok, so lets clarify few things.
Atari ST has 8MHz while Amiga has only 7.19. This means each raster line in Atari ST has more cycles to be used - mainly in off screen area, thats why the border is larger.
Atari ST register change using CPU takes as much cycles as done it by Copper, the difference in approach lies elsewhere.
Atari ST Hires is using only 2 bitplanes so 4 colors total, and you can change single color every 16 pixel plus all total 4 colors change every line. You can also precache those 4 colors.
On Amiga considering hires you can have following modes:
1. 2 Bitplane 4 colors and single color change every 16 hires pixels plus all total 4 colors change every line. You can also precache those 4 colors.
2. 3 Bitplane 8 colors and single color change every 32 hires pixels plus all total 8 colors change every line. You can also precache those 8 colors.
3. 4 Bitplane 16 colors - you can not change any color within the line but you can change total 14 colors every line as long as you wont use Overscan.

IMHO the in most cases best results can be seen on option 3, but actual result can vary from picture to picture. On those page you brought the examples where wiselly chosen and represent easy targets, but if you would look at the girl you would see plenty of limitations this mode 1 brings.

Because Atari ST has smaller picture most popular are Overscanned Lowres 416x272x52cc/line, which if you would put 2 monitors side by side looks like middleres compared to Amiga.
In this mode you can have 4 Bitplane 16 colors and single color change every 8 pixels plus all total 16 colors change every line.

Bottom line Amiga can do everything what ST can, while ST programmers are doing everything so we would falsely think ST can also do everything what Amiga can ;-)

Last edited by Trachu; 09 May 2017 at 18:11.
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