NVIDIA GeForce GTX480 Video Card Review :: Tessellation

03-26-2010 · Category: Hardware - Video Cards

By Benjamin Sun

One of the problems with modern graphics card architectures is that while the pixel pushing and texture pushing power of the latest cards has improved over 150x over the GeForce FX 5800 from 2003, the pure triangle power of the cards has only increased a mere 3x. So while we have pixel and texture fill rates in the billions we have triangle rates of several hundred million at best.

So what is tessellation anyway? Tessellation is the creation of complex geometry by combining a low-polygon model with a mathematical description of a more complex higher polygon model. If you look at a character in a game like Far Cry 2 or Call of Duty Modern Warfare 2 they look faceted due to the use of polygons. As more polygons are used in the models the characters become smoother looking. The problem is the more complex characters take a lot more bandwidth to generate without tessellation. Tessellation allows a game developer to use a simple mesh for an object, tessellate it by subdividing the polygons in the object and adding a displacement map to the object to make it have geometry and detail.

Tessellation saves bandwidth by having the simpler object animated requiring less bandwidth than using the more complex object move through frame by frame. You can also add a displacement map which can generate complex terrain or add complexity to an in-game object or character model by changing the geometry of an object. DirectX 11 tessellation has two programmable stages, Hull Shaders and domain shaders. Hull shaders do the LOD calculations for the subdivision of existing polygons on a simple model. The Tessellators create new geometry from those calculations. Domain shaders evaluate the object created by the tessellation and can apply a displacement map to the objects. One of the cool things with tessellation is you actually create geometry so when a bullet hits a wall, for example you actually create fragments which can interact with the environment.

NVIDIA has released a few demos with the card to show off tessellation. The Island demo shows off the ability of the card to do tessellation by doing realistic physically simulated waves. The demo uses DirectX 11 tessellation and supports both static and dynamic tessellation. The Hair demo is realistically simulated, created and rendered on the GeForce GTX 480 by using the parallel tessellation engines. The hair billows and cascades naturally with accurate physical properties. Realistic hair is usually only seen in demos as the games use hats and caps to hide the hair. The Supersonic Sled demo uses PhysX, DirectX 11 and 3D Vision. There is a scene with 1 million particles when the bridge breaks up. The Raging Rapids demo uses PhysX to show realistic water movement.


NVIDIA GeForce GTX480 Video Card Review Supersonic Sled

Supersonic Sled

NVIDIA GeForce GTX480 Video Card Review Island

Island

NVIDIA GeForce GTX480 Video Card Review Hair

Hair

NVIDIA GeForce GTX480 Video Card Review Raging Rapids

Raging Rapids