<u>HDR Rendering with the NVIDIA GeForce 6800Ultra:
Certainly from our perspective, the most interesting addition to CryEngine is the High Dynamic Range rendering function that is supported by the GeForce 6 series. This is a massive leap forwards on the image quality front - everything just looks so much more realistic. The feature is basically used to simulate human eye's reaction to light by using a greater range of brightness to emulate what we see in reality. In reality, if you were to move from a building outside in to a bright sunny day, your eyes have to adjust to the difference in light volume. Initially, this difference can be blinding, at least, until your eyes have adjusted to the change of lighting - this particular method of HDR goes to great lengths to simulate this, and we feel that it does a pretty good job of it.
There are other methods for achieving High Dynamic Range rendering, which have support for ATI's boards; these include the rthdribl
demo, as well as ATI's own HDR demos. The method used inside Far Cry 1.3 is the OpenEXR method
. This uses FP16 frame buffer (a 16-bit floating point), which is only supported by NVIDIA's GeForce 6 series - the GeForce 6 series supports both FP16 and FP32. At present, ATI use a 24-bit floating point precision that does not support floating-point blending, filtering or colour buffers, which means that ATI's boards are not compatible with OpenEXR's HDR method.
To make use of Far Cry's HDR feature, you must have a GeForce 6 series graphics board, and Anti-Aliasing must be disabled. This feature is not compatible with Anti-Aliasing at the moment, as both floating-point blending (the technique used to create the HDR effect) and Anti-Aliasing are processed in the last stage of the pixel output engine (also known as a ROP) in order to function correctly.
If you are feeling adventurous, and are interested in testing this feature out on your GeForce 6 series' graphics card, we recommend that you lower the resolution before turning HDR on, as this feature has a serious performance hit - we found that 1024x768 gave the best results. Toggle the console and type 'r_hdrrendering X
', where X is an integer between 1 and 11 - there are 11 different HDR effects in Far Cry. Ubisoft indicated that 'r_hdrrendering 7' provides the best image quality, we agree with them, but we also found a slightly less performance taxing setting of 'r_hdrrendering 3', which still provides some very realistic lighting effects.
Image Quality - HDR '0' vs. HDR '7':
We see here that in darker environments with a light source, HDR rendering makes the scene generally lighter - this is a result of the bloom created by the light source; certainly in the second screenshot. There is a great improvement on the tiles in 'Cooler' and 'Archive' levels - the reflections from the light source are nothing short of impressive.
The moonlight reflects very well off the surface of the water too, which gives a more realistic feel to the surroundings. This is displayed in the screenshot from the 'Regulator' level. In lighter levels such as 'Fort', the scene is darker and there is a much more textured look to the vegetation and surrounding scenery. The water in 'Fort' is also more realistic, much like the moonlight, the sunlight has some positive effects on the reflective properties of the water.
We have used the same manual run through that we have used throughout this article, taken from the start of the 'Factory' level. It shows some good lighting effects, as can be seen in the first and second screenshots of our image quality comparison above. We have left the game details set to their maximum selectable setting, as shown on the first page. Everything is set to 'Very High' with the exception of Water Quality, which was set to 'Ultra High'. We have used 8x Anisotropic Filtering, and AA was disabled, as discussed above. Finally, we used 1024x768 for our testing resolution, as this provided the 'best playable' results.
We expected the performance hit to be quite large, but we were not expecting it to be hit in this fashion - the deficit is massive! At the moment, we are unsure whether this performance deficit is really worth the extra quality that we are experiencing here, but it is well-worth checking out, as it is an interesting effect to behold. I actually went through and completed the game again with HDR enabled, as you just have to see it, to realise how good the effect really is - screenshots just don't do it justice, so you will have to take our word for it.
More Image Quality... HDR '3' vs. HDR '7':
Some of you may find 'r_hdrrendering 7
' a little choppy in places, so we also ran several tests using 'r_hdrrendering 3
' for comparison purposes. We did not see massive improvements in average frame rate (a mere three frames per second), but we did see a five frames per second increase in the minimum frame rate, bringing it up to the levels of performance without HDR enabled.
A lot of the scenes look very similar, with the exception of some rather massive differences in the vegetation on the 'Fort' level. The grass appears to be very burnt, almost like someone has used a giant magnifying glass to singe every blade of grass. You can also see this, albeit not quite so apparent, in the first screenshot, which is taken from a part of the 'Factory' level that we have used for our manual run through.