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A question regarding the video chip
Posted: Fri Oct 12, 2012 1:55 am
by Bitybity
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.
Posted: Mon Oct 15, 2012 6:37 pm
by Chilly Willy
It's not 3D, but could be used to help with 3D. Start by reading the SCD manuals.
Posted: Mon Oct 15, 2012 6:40 pm
by djcouchycouch
Chilly Willy wrote:It's not 3D, but could be used to help with 3D. Start by reading the SCD manuals.
Like here?
http://www.retrodev.com/segacd.html
and here?
http://www.retrodev.com/scdgfx.txt
Posted: Mon Oct 15, 2012 9:06 pm
by Bitybity
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.
Posted: Mon Oct 15, 2012 10:13 pm
by Chilly Willy
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.
Posted: Tue Oct 16, 2012 3:07 pm
by slobu
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?
Posted: Tue Oct 16, 2012 4:46 pm
by Chilly Willy
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.