Parhelia RGBA format.... questions...

[Panajev2001a]

Matrox talks about 10 bits RAMDAC and 10 bits per color component...

R:G:B -> 10:10:10 but with a 32 bits framebuffer we only have 2 bits for alpha... wouldn't make sense having a 30 bits framebuffer and a 38 bits back-buffer ?

 

[ERP]

As I think has been mentioned here before destination alpha isn't used much. It has some potential, but many current implementations reduce it's usefulness.
As long as you can still choose to use 8 8 8 8, I don't see an issue.
I do question whether 10 bit frame buffers is really a big step forwards, It might reduce some accumulation artifacts, but I'd really like to see 16 bits per color or preferably 32 bit fp, since these are more useful for vector storage. It might also be possible to use some sort of format with a shared exponent which might be enough, say 11, 11, 11, 7 where the 7 is a shared 7 bit exponent.

 

[Panajev2001a]

I heard that thing about destination alpha too that's why I said 30 bits front buffer and 38 bits backbuffer... is this a stupid idea or worth something ?

 

[ERP]

I heard that thing about destination alpha too that's why I said 30 bits front buffer and 38 bits backbuffer... is this a stupid idea or worth something ?

Destination Alpha is meaningless in the front buffer, so it's save some memory. You could even go to a 24 bit front buffer without loosing very much. Most cards don't do this though, since they don't posess the logic to address 24 bit chunks of memory directly. As a result in D3D you end up with front buffer formats like R8G8B8X8, where the X values are just undefined garbage.

 

[3dcgi]

Most hardware can't address 38 bit chunks of memory very easily that's why you always see everything as 32 bits, 64 bits, etc.

 

[Humus]

Destination Alpha is meaningless in the front buffer, so it's save some memory. You could even go to a 24 bit front buffer without loosing very much. Most cards don't do this though, since they don't posess the logic to address 24 bit chunks of memory directly. As a result in D3D you end up with front buffer formats like R8G8B8X8, where the X values are just undefined garbage.

Meaningless? I think that's going a little too far. Sure, it's not the most used, but it sure has it's uses. For instance I've used it for volumetric fogging.

 

[pcchen]

Well, it's meaningful in back buffer, not front buffer
I also have used destination alpha to store dynamic light luminance for multi-pass rendering.

 

[Humus]

Aaah, the front buffer, was thinking frame buffer.
Yeah, in the front buffer it's meaningless.