FP blending in R420?
- Thread starter Mintmaster
- Start date
Mintmaster
Veteran
I think that's what everyone calls integer nowadays. The range that the values actually represent is pretty meaningless aside from a scale factor that may need to be done.
I guess FX is somewhat more correct because it means "fixed point", but I always thought of that as an NVidia term. Not only is NVidia's "internal FX12 units" the first time I saw it, but I don't see why I have to be reminded of the GeForceFX, IMO the most poorly executed graphics architecture from either of the big two for many years.
I think the best (though incomplete) solution is just do blending in the final R8G8B8A8 buffer. You won't get HDR effects from things like reflections off transparent windows, and you'll have to use texkill instead of alpha testing, but you'll at least get most of the effect with minimal effort. Tone mapping could be a serious problem, though.
The biggest shortcoming of this solution is that things like propulsion flames or futuristic weapon fire won't be able to get HDR effects applied. One possibility is to just use alpha textures with halos/glows/streaks already applied, as they often do in today's games. The other possibility is to just go Tron 2.0 style for all alpha blended effects, and do a fake HDR using ordinary R8G8B8A8 buffers.
Yes, it is disappointing that ATI skipped FP blending support, but there's still plenty of HDR effects available. It's possible that some of these hacks could increase performance on NV40 as well.
I guess FX is somewhat more correct because it means "fixed point", but I always thought of that as an NVidia term. Not only is NVidia's "internal FX12 units" the first time I saw it, but I don't see why I have to be reminded of the GeForceFX, IMO the most poorly executed graphics architecture from either of the big two for many years.
I think the best (though incomplete) solution is just do blending in the final R8G8B8A8 buffer. You won't get HDR effects from things like reflections off transparent windows, and you'll have to use texkill instead of alpha testing, but you'll at least get most of the effect with minimal effort. Tone mapping could be a serious problem, though.
The biggest shortcoming of this solution is that things like propulsion flames or futuristic weapon fire won't be able to get HDR effects applied. One possibility is to just use alpha textures with halos/glows/streaks already applied, as they often do in today's games. The other possibility is to just go Tron 2.0 style for all alpha blended effects, and do a fake HDR using ordinary R8G8B8A8 buffers.
Yes, it is disappointing that ATI skipped FP blending support, but there's still plenty of HDR effects available. It's possible that some of these hacks could increase performance on NV40 as well.
It sounds to me like you're saying, "If game developers do things the way they've been done for the last couple of years, performance could increase on the NV40." Huh? There's a reason why the move for FP filtering/blending, and it's so that games move forward, not backwards.Mintmaster said:
Joe DeFuria
Legend
Chalnoth said:
Why does NV40 support sport FP16 again?
Joe DeFuria said:
If you're asking why is doesn't support FP32 but only FP16 for FP blending, you already know the answer Joe: Way too much memory bandwidth overhead to be usable this time around.
Full FP32 support on the math side (silicon) of things was probably do-able, but we don't have mem bandwidth in surplus so it was better to come up with a good alternative (FP16) than have nothing at all (FP32). (Forget about the FP16 fiasco from the NV3x with the NV4x me says...)
DaveBaumann said:
Did ATI leaving out fp blending in the R420 have something to do with their use of fp24 instead of fp32/fp16?
I'm assuming since the bandwidth hit for doing fp16 is as high as it is that fp24 would be even larger and possible unacceptable with today's memory.
Mintmaster
Veteran
Chalnoth said:
I have no idea why you just said what you did.
How many games support even close to R300's HDR capabilities in the "last couple of years?". Zero. That's what I'm saying. Plenty can still be done.
You think I'm arguing against the support of FP blending? Have you been paying attention to ANY of my posts in this thread? Don't try to make me look like a blind supporter of ATI, because I'm not.
I'm just saying that if developers choose to put a R3xx HDR path in their game (which would be smart if not downright necessary given the current market share), then NV40 could run it too if FP16-blending was too bandwidth intensive and caused a performance drop that some would deem intolerable. Geez, just look at my intentionally inconclusive statement. There are three qualifiers - "possible", "some", and "could". Obviously taking advantage of NV40's FP blending/filtering in an HDR implementation is the most straightforward, easiest, and most complete solution out there.
