High Dynamic Range Lighting Performance
High Dynamic Range (HDR) lighting is an attempt to replicate in software the exact way in which the human eye sees and comprehends lights. In real life, humans can see a very distinct difference between different lighting amounts in the low light ranges (ex: walking through your house in the dark) but see blurring and distortion when lights are extremely bright (ex: walking towards a car with bright lights on). In game though, today’s monitors do not have the ability to display lights of that magnitude and thus we have today only a portion of the lighting environments we can see.
Far Cry’s 1.3 patch gives the user the option to enabled HDR lighting in the game using the “/r_hdrrendering 7” tag in the console. You must have either a GeForce 6 series card or one of these new 7800 GTX cards for it to work, and you must also disable any AA in the control panel or game menus. Here are a pair of screen shots of the Regulator level showing HDR enabled vs HDR disabled.
HDR Disabled – Click to Enlarge
HDR Enabled – Click to Enlarge
While it may simply appear that everything is brighter in the second image, in fact we are simply seeing a greater contrast between darks and lights. Unfortunately, HDR lighting is extremely computer intensive and it takes a lot of horsepower to do it. Here are some benchmarks comparing the 7800 GTX and 6800 Ultra cards in SLI mode in Far Cry v1.3 performance.
You can see that compared to the 6800 Ultra cards running in SLI mode, the 7800 GTX is a massive improvement in HDR gaming performance. A single 7800 GTX is about 2.28x faster than the pair of 6800 Ultra cards. Unfortunately though, the 7800 GTX cards don’t see a very big gain working in SLI mode.
ATI has planned HDR support in their upcoming R520 core and have demoed it running on several occassions. Hopefully they can at least match the HDR performance NVIDIA is showing here so we can begin to see more games taking advantage of this improved lighting technique.