SM 3.0/HDR

FiringSquad: Which aspects of shader model 3.0 are you taking advantage of?

Cevat Yerli: We’re using looping and branching mainly. We’re using the floating point FP16 FP 32 of course. But mainly we’re using the aspect of making sure that more lighting can be accomplished with flow control and branching so we can encode for example 4 lights in one pass, which is speeding up the rendering. Our utilization of 3.0 shader model is essentially tied to performance improvements. So for example we can render, previously with 2.0 we were rendering one light per pass and now we’re rendering up to four lights per pass.

Second aspect is that we’re using geometry instancing which is a big performance gainer, mostly for outdoors but also for indoors. On the outdoors we’re using for example to reduce the draw calls from trees, grass, and other vegetation objects, we’re using the same or similar object meshes in different positions and orientations. They’re rendered in one draw call with different attributes in the vertex shader. That reduces the draw calls.

GeForce 6800 GT 4xAA/8xAF SM2.0

GeForce 6800 GT 4xAA/8xAF SM3.0

X800 XT 4xAA/8xAF

FiringSquad: Are you using dynamic branching for the lighting or static branching?

Cevat Yerli: We’re using static branching. We’re using static because [with dynamic] there were a few performance problems there so we decided to use static branching ultimately to utilize the best features of 3.0. I was telling people previously at the launch event that the 3.0 shader model itself is great and all that but you have to use it [dynamic branching] wisely because it’s a very powerful subset and you can very easily get into a situation where branching is great but it will slow down your technology, and since that’s the case we’re using static branching to still get the performance up with our technology.

FiringSquad: How long did it take to integrate SM 3.0 into Far Cry?

Cevat Yerli: The first version of it was pretty much done in 2 weeks up and running, but overall we spent approximately four weeks with two guys.

FiringSquad: One new feature NVIDIA has added to GeForce 6800 is support for HDR. How does NVIDIA’s solution differ from ATI’s?

Cevat Yerli: It’s more about the FP16 versus FP32 format. We’re using it [FP32] for HDR, which is not supported by ATI. That is to deliver very high image quality. But, I have to tell you HDR isn’t officially going to be part of the 1.2 patch.

FiringSquad: Do you plan on adding high dynamic range lighting (HDR) in the future?

Cevat Yerli: Yes definitely. It’s going to be officially supported in 1.3. Which will be coming out hopefully soon. [laughs] The reason why it’s not enabled now is because there are quality issues we have to check, we have to go back and look at it because it's a content-specific application. The technology works but it requires the content to be adapted to it, otherwise you have overexposure, you have too many objects on the screen glowing and things like that. And while that looks cool on screenshots, when you’re playing that’s not as cool. So we need to tweak it and make sure it matches the content.

FiringSquad: So that’s what you guys are playing with right now, just tweaking it until it looks just right?

Cevat Yerli: Yes but we couldn’t do it in such a short amount of time, so we plan to launch it in the next patch. What will be part of patch 1.2 will be the performance gains.

FiringSquad: So basically your requirement for HDR is FP32?

Cevat Yerli: Yes FP32 blending.