**Update** This post is somehow outdated and I just lost this small demo. Sorry for that.

Hello there, next post!

Here no relationship with ray tracing; on the contrary, it is all about rasterization and tesselation.

First, some screen shots of the demo provided with this post:

Hello there, next post!

Here no relationship with ray tracing; on the contrary, it is all about rasterization and tesselation.

First, some screen shots of the demo provided with this post:

A close up on the tesselated surface in wireframe mode (10,000,000 triangles). About 200 millions triangles per second are displayed on my low-end 8400GS (Here the frame rate is lower due to the wireframe mode slow on Nvidia)

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A simple procedural displacement is applied on the tesselated mesh

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This technique actually relies on several techniques developed by Tamy Boubekeur.
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A simple procedural displacement is applied on the tesselated mesh

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- Patch Tesselation

The first thing to do is to tesselate the input mesh. To achieve this, we simply replace each triangle by a patch, i.e. a set of barycentric coordinate triangles. Then, instead of displaying each triangle, we replace each of them by an instanciated patch. In the demo, we therefore create two vertex streams. The first one contains all the data for each triangle and another one simply contains the barycentric coordinates of the triangles of a patch. Then, the instanciation ability of Direct3D allows us to repeat the patch along the surface of the object. For more details about the technique, may one refer to the Graphics Hardware '05 article by Tamy here. However, in this article, no Direct3D instanciation is used.

So, why is this method good? Actually, if the patches are large enough (i.e. if the tesselation rate is high), the pre-transform and post-transform caches used by the GPUs become more and more efficient so that we directly get the maximum theoretical performance of the rasterizers. For example, the frame rate does not change when you use 64 times more triangles. In fact, we can expect the same level of performance for the GPUs which will support tesselation units.without the need to use any hand-coded patches. In my 8400GS, I got 200 millions triangles per second but we may easily expect 1 billion triangles per second on DirectX11 GPUs.

By the way, I use in the demo a simple optimization of the patch using the very good and simple indexation optimizer, "Tipsify" (you may find the reference here). This reorders the patch indexation in linear time using only triangle / point adjacency while maintaining a very good level of performance (and this is much simpler and much faster that stripification algorithms like TriStrip or NvStrip).

So, why is this method good? Actually, if the patches are large enough (i.e. if the tesselation rate is high), the pre-transform and post-transform caches used by the GPUs become more and more efficient so that we directly get the maximum theoretical performance of the rasterizers. For example, the frame rate does not change when you use 64 times more triangles. In fact, we can expect the same level of performance for the GPUs which will support tesselation units.without the need to use any hand-coded patches. In my 8400GS, I got 200 millions triangles per second but we may easily expect 1 billion triangles per second on DirectX11 GPUs.

By the way, I use in the demo a simple optimization of the patch using the very good and simple indexation optimizer, "Tipsify" (you may find the reference here). This reorders the patch indexation in linear time using only triangle / point adjacency while maintaining a very good level of performance (and this is much simpler and much faster that stripification algorithms like TriStrip or NvStrip).

- Approximation of Subdivision Surfaces

The tesselation algorithm via the Direct3D instanciation is the core system to provide many triangles. However, the way triangles are generated (via tesselated patches) does not seem appropriate to the evaluation of subdivision surfaces since they are complex recursive algorithms. (By the way, one may find excellent references and details on subdivision surfaces in the awesomo tutorial located here). In the article, QAS (located here), Tamy proposes to replace the recursive evaluation of the subdivision surface by an analytical approximation. The principle is pretty simple: first, project the triangles vertices and the middle of every edge on the limit surface (i.e. the subdivision surface) and compute a quadratic Bezier triangle which fits these 6 points (the vertices and the edge middle points). This leads to a pretty fast and nice approximation of subdivsion surfaces.

Enjoy!

- About Adaptive Tesselation

- Some Details about Asset Production

- The Demo

Enjoy!