a little tech help please (vdp related)

[Coolgame]

i plan on making a new game, but to be honest i dont know what to to decide on, maybe a 3d fighter.

im doing a little saturn 3d modeling right now (i'll post up some of my work you'll be please) and is

trying to get the hang of vertice animation.

but that's not the point (i was just letting you know where im at right now, but to the question)

I have a question that been eating me for a while and i cant really find a clear answer,

though i think i know the answer i'll ask you all to be sure.

can the vdp1 character address command table CMDSRCA (you know the one that you have to write the address

divide by 8H in) read/access pixel data store in other areas of memory, like the main ram and/or cart vram.

im not taking about the scu's dma transfer command but access by the vdp1 itself to other rams other

then it's own vram.

in other words if i was to write a adress in the character address command table CMDSRCA like the main ram

or vram cart (1mb-4mb) will the vdp 1 read/access that data?

i read that the vdp2 can access the sh2, main ram and scu.

please help

 

[Chilly Willy]

Neither VDP can access anything other than VRAM. You can use either SH2 or the SCU to transfer data to the VRAM for them to use, but they cannot access any other memory region in the Saturn - well, VDP1 writes the frame buffer, but other than that and the VRAM, it cannot access anything else.

 

[antime]

As an additional note, since the chips can only access local memory that also means the addresses you put into the registers and tables are local addresses, ie. VDP1 VRAM starts at address 0x0 and not 0x5c00000 where it resides in the global address map.

 

[Coolgame]

i kind of figure it couldn't, but what i want to do is find a way to scale picture data from one source like the

vram cart to the vdp1, being how the vdp1 read and ignore data base on scale setting, i was hoping it could read

from another ram source other then it's own to save me the hard task of doing so by software code programming.

does anybody have any suggestin to scaling pixel data outside of the vdp1's vram without the help of the vdp1?

it'll come in handing with dealing with level of detail with changing camera zoom of close and far away

and large number of polygons on screen.

 

[antime]

If you really want to use VDP1 then you'd first have to transfer the source image to VDP1 VRAM, use VDP1 to scale it to the desired size and then read back the result from the framebuffer. However this is pretty much guaranteed to be a lot slower (not to mention more complicated) than doing it purely in software. Using software also lets you use much higher-quality scaling algorithms.

If your intention is to use texture mipmaps then I would suggest precalculating them offline.

 

[Coolgame]

thanks everybody you be a great help.