Depoends on the type you use. OpenEXR (ILM's version) requires FP16 blending and as such can only be done on NV40/G70/R5xx hardware.
However there are other forms of HDR out there, and they have been supported on older cards like Cleeve mentioned. FXs can support the older syle of HDR, just not very well (like 1/4 speed of equivalent R9xxx series card), even the NV40s had trouble.
I though only newer cards have this feature, or 'supports' HDR? Is HDR software based?
That the OpenEXR method of HDR, HL2 actually supports both methods, as does SplinterCell3. HDR can be done in software but at a terrible performance hit (except on a server). Remember also that HDR is a lighting support method it is also applied to 2D photos. If you were to do the effect from FartCry in software you could expect to see framerates in the seconds per frame, not frames per second. Also effect can be mimiced with software/hardware workarounds. While it's not supported in FartCry you technically could achieve the same lighting effect with an R3xx/4xx series card with multiples passes (would require 3 to match the same levels (actually at FP24), however that would be a drastic performance hit, where an X850XT would likely perform as fast as a GF6600GT or worse for the same segment (rememebr that's considering that this is a game that usually has higher framerates on the X8xx series to start with). In order to make that work properly would require a fair amount of additional work from the developer, not worth really it in that case.
HDR is a tricky issue, and there's far more BS out there than fact, but really the main thing to remember is that it's up to the developer to decide what they will support.
Technically both the X1800 and GF7800s can support higher than FP16 HDR, but no one is going to go to that step because that would shut-out the GF6xxxs.
IMO the best solution for gamers is that of SplinterCell and HL2 where you have a choice, however the best solution for developers is probably sticking to a single format, which is likely to be OpenEXR for the foreseable future.
- You need a licence to buy a gun, but they'll sell anyone a stamp <i>(or internët account)</i> ! - <A HREF="http://www.redgreen.com/" target="_new"><font color=green>RED </font color=green> <font color=red> GREEN</font color=red></A> GA to SK