NVIDIA’s GeForce GF100 Under the Microscope

by Michael "SKYMTL" Hoenig     |     January 17, 2010

The Future of Games: Attaining Geometric Realism

Today’s GPUs are interesting beasts that have been tailor-made for their associated APIs but when adding advanced rendering techniques they are quickly brought to their knees. Basically, DX9 and DX10 were all about pixel shading horsepower over all else and current GPUs excel in this department but DX11 is another matter altogether. It adds features such as tessellation which doesn’t necessarily increase the amount of shading horsepower needed but adds new options for geometric realism.

One of the main issues with past generations is that while there was serious headway made when it came to increasing shading power, the same couldn’t be said for geometry performance. NVIDIA gave an interesting example by stating that the GT200 had about 150 times the amount of peak shading performance as their FX5800 but less than three times the amount of geometry performance.

So let’s take a look at what it takes for geometric realism.

If you look at the picture above from Far Cry 2, it’s apparent that the textures and shadows are extremely detailed as is befitting for today’s higher-end DX9 and DX10 architecture. However, upon closer inspection there are several things about the scene that could be done a bit better through increased geometric detail. Surfaces like the gun holster and the woman’s shoulder that should be mapped smoothly look slightly jagged while characters normally have their hair covered...or their hair just looks like a helmet. The problem lies in the fact that a large amount of geometric detail is needed to accurately model these items and current GPUs don’t have the horsepower to do that. As such, developers’ hands are tied even if they wanted to add higher levels of detail.

Non tessellated images on left, DX11 tessellation on right

So what kind of tools do developers have at their fingertips in order to increase the level of geometric detail while not overly impacting performance? To begin with, DX11 offers several paths which can be used for heightened yet efficient rendering of geometric detail while offering several similarities with past APIs to decrease the learning curve.

Notably, tessellation can increase geometric detail as you can see in the images above while adding new three-dimensionality to objects. If you are fortunate enough to have a card capable of using the Unigine program in DX11 mode, you will be able to see how displacement mapping combined with tessellation allows for some structural occlusion and increased detail levels. As such, shadows can become a reflection of the geometry and can move around dynamically as the light source moves.

While software tessellation on the CPU is possible, the information still has to be shipped over the PCI-E bus before making its way to the GPU. This is an inefficient and time-consuming process that will slow a system down to a crawl in fairly short order. DX11 on the other hand offers computational efficiency by moving all of the operations onto the GPU itself.

Another tool in the DX11 developers’ bag is a truly dynamic level of detail (LoD) that increases the detail as you approach a given object. Dynamic LoD saves on resources since the system isn’t forced to render several high-detail objects within a scene at the same time and gives priority to objects closer to the viewer.

Certain compute aspects of DX11 can also be added to tessellated scenes to give a sense of realistic movement without the need for vast CPU resources. This is where DirectCompute comes into the equation since it allows animations (among other things) to be done directly on the GPU in concert with rendering. Both hair and water were infinitely hard to render within past APIs but the images you see above were rendered in real-time on GF100 hardware through the use of tessellation, DirectCompute and selective geometry shading.

Even though developers are a huge part of the process, the real trick is to make an architecture that allows all of these operations to be done efficiently and without the resource-hogging overhead of today’s GPUs and APIs. As we get further into the technological aspects of the GF100 architecture, you will begin to see how NVIDIA has made effective use of the tools within DX11 and have an architecture built from the ground up for this API.

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