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Nixus Minimax

Posts 416
12 Nov 2018 09:05


BTW, one very nice thing with modes that effectively only have 6 bitplanes is that you can keep all the data inside the registers during c2p. That makes c2p much faster. That is one reason why effects with some chunky mode main effect and some 2d overlays are so popular in many demos. They look cool and they are much easier on the CPU for c2p.



Renee Cousins
(Apollo Team Member)
Posts 139
13 Nov 2018 00:14


Michael Borrmann wrote:

    The problem I especially see here is, that while you avoid that effect for BOBs by using four different RGBG rotations on your BOBs, the scrolling tiles won't.
   
    If you don't want to scroll by 4 pixels, which would look very jerky, you would need four different versions of each tile as well, and blit these each and every frame into the screen buffer.
   
    Which is not an option on a system below a 68040 config, I guess.
   
    This mode could work and look interesting on non scrolling games, though.

Scrolling in all directions is no different than regular screen modes. The RGBG pattern is not fixed and would scroll right along with all the other planes.


Renee Cousins
(Apollo Team Member)
Posts 139
13 Nov 2018 00:17


Nixus Minimax wrote:

  I would have thought that you'd also have to DMA the two control bitplanes and thus use 6 and 8 bitplanes, respectively, for HAM6 and HAM8. Is there a dirty little trick like disabling DMA and writing a fixed value to the DMA registers for the control bitplanes?

Yar. You write $7200 to BPLCON0 and you get Agnus fetching DMA for four bit planes while Denise assumes all six are active.

It's super handy that the two bit planes which are not fetched are also the control planes for HAM. So you can get RGBG in there by simply writing manually to the to DAT registers. If you want to be really fancy, use the COPPER to switch then every scan line to alternate the red and blue changes.

Sadly this trick does not work on AGA.


Renee Cousins
(Apollo Team Member)
Posts 139
13 Nov 2018 00:19


Nixus Minimax wrote:

BTW, one very nice thing with modes that effectively only have 6 bitplanes is that you can keep all the data inside the registers during c2p. That makes c2p much faster. That is one reason why effects with some chunky mode main effect and some 2d overlays are so popular in many demos. They look cool and they are much easier on the CPU for c2p.
 

Its even faster with 4-bits!

And even faster-faster when you don't have to C2P at all.


Michael Borrmann

Posts 133
13 Nov 2018 06:06


Renee Cousins wrote:

  Scrolling in all directions is no different than regular screen modes. The RGBG pattern is not fixed and would scroll right along with all the other planes.

Then this sentence was a red hering by you:


In AMOS, open a 320x200 screen and create a custom copper list for it writing $7A00 into BPLCON0 (7-bitplane mode, HAM enabled) and then use the COPPER to write BPL5DAT and BPL6DAT with the RGBG patterns described above before each scan line.

If you use the copper for that, it would be static, if you not use 4 different copper lists.

By omitting this, your approach makes a lot more sense, I concur..




Fano Il Primo

Posts 2
28 Jan 2019 14:31


The Neo Geo used cartridges and as had happened in the End Of Life of the SNES (SuperFX permitted rudimental 3D on SNES!) they used custom chips a lot... it is for this that Neo Geo games could easily cost 600$ there is a lot of the console hardware in them!

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