What is Tessellation?

Learn its effect on gaming graphics

Tessellation isn't the hot new graphics technology it once was—leave that to ray tracing—but it's still one of the most important technologies used in games to make their virtual worlds feel more real and alive. It does that by tiling flat geometric shapes with no overlapping or gaps to add a lot more depth to objects and characters, and make everything feel more 3D and immersive.

It can also make the developmental process easier.

Tessellation and Working With Triangles

Introduced with DirectX11, Tessellation is, by itself, a method for increasing detail in a scene by subdividing the triangle meshes that make up objects and characters in game worlds. Tessellation allows for massive division of those triangles, whereby each halving (or doubling, depending on your perspective) creates ever finer details because the edges are less stark, and models more nuanced.

This alone wouldn't create a drastically improved effect. Perhaps adding a layer of detail to an image that wasn't otherwise there, but artistic texturing alone can do that. Tessellation is special because it's combined with displacement mapping (it's a little different from bump maps). That is, effectively, a texture that can store information about its height—how far it protrudes from its base.

Tessellation games and benchmarks utilize this to create objects and scenery with much greater depth. Although it's typically employed in tandem with other visual techniques, the Unigine Heaven benchmark gives a stark reminder of just how powerful tessellation can be in the right circumstances.

Tessellation in Unigine Heaven

In the above image you can see that the stairs, which were previously a flat ramp with a stair-like texture on it, turns into a 3D representation of a staircase with tessellation applied. This is an extreme case—no game developer would rely exclusively on tessellation for such an important visual feature—but it shows what an impact tessellation can have in the right circumstances.

Why Use Tessellation Graphics?

As much as the tessellation effect in benchmarks like Unigine Heaven is pretty, it's certainly not astoundingly so—especially in 2020. But it's also not unique. There is no reason that such a 3D visual effect couldn't be achieved by creating a model that is of that depth and scale and texturing it appropriately. So why do we use tessellation graphics instead?

The ultimate reason is because it's easier and it's cheaper. Not in terms of dollar cost, but in terms of system resources. It's a lot easier to create a low detail model, with a high quality texture and displacement map applied to it, than it is to create a highly detailed model to go along with the texture. That makes it a lot easier for the developer to create detailed scenes using tessellation

Tesellation Games: What's the Impact?

With Tessellation's ability to have an extreme effect on visuals, even if that's not always realized to the same extent, what effect does it have on games? Will turning on tessellation in your game of choice tank your frame rates?

Not typically. Head to head tests in popular games that utilize tessellation, like GTA V, suggest the impact is minimal, losing only a few frames per second in even the most demanding of instances with heavy tessellation at play. SapphireNation's in-depth analysis shows that effects like HDR and depth of field can have a far greater impact on performance than anything tessellation requires.

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