A question regarding the video chip

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Bitybity
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A question regarding the video chip

Post by Bitybity » Fri Oct 12, 2012 1:55 am

Hi, everyone.
First of all, I must thank all of you for your answers in other questions =)

I have another question: Could you tell me, how I can use the 3D chip from the Sega CD? I have no a minimal idea about this.

Thanks for your help, and excuse my bad english.

Chilly Willy
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Post by Chilly Willy » Mon Oct 15, 2012 6:37 pm

It's not 3D, but could be used to help with 3D. Start by reading the SCD manuals.
:D

djcouchycouch
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Post by djcouchycouch » Mon Oct 15, 2012 6:40 pm

Chilly Willy wrote:It's not 3D, but could be used to help with 3D. Start by reading the SCD manuals.
:D
Like here? http://www.retrodev.com/segacd.html
and here? http://www.retrodev.com/scdgfx.txt

Bitybity
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Post by Bitybity » Mon Oct 15, 2012 9:06 pm

Argh, I'm hard. I can't understand the guide D:. All of what I know, is it needs a lot of Word RAM, and in Sonic CD, for using this chip, the code is run in RAM.

Chilly Willy
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Post by Chilly Willy » Mon Oct 15, 2012 10:13 pm

djcouchycouch wrote:
Chilly Willy wrote:It's not 3D, but could be used to help with 3D. Start by reading the SCD manuals.
:D
Like here? http://www.retrodev.com/segacd.html
and here? http://www.retrodev.com/scdgfx.txt
No - like here: http://www.romhacking.net/documents/278/

And there are no real examples of using the graphics ASIC, even from SEGA. Well, not any that have surfaced. I mean to do some examples eventually, but it's down the todo list a ways.

slobu
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Post by slobu » Tue Oct 16, 2012 3:07 pm

That document references something called "Full Graphics Function" Is that a special pixel based video mode? Or, is it just faking it by writing to tiles?

Chilly Willy
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Post by Chilly Willy » Tue Oct 16, 2012 4:46 pm

slobu wrote:That document references something called "Full Graphics Function" Is that a special pixel based video mode? Or, is it just faking it by writing to tiles?
It's a byte expansion/contraction mode. It allows you to read/write the word ram in bitmap format on the SCD side, while reading it in tile format on the MD side. Note that you read/write bytes on the SCD side, but the top four bits are ignored on writes, and read as 0. It's just a mode to make bitmaps easy to handle on the SCD while presenting the result to the MD side in the tile format the VDP needs.

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