STAR TESSELLATION HOW TO
STAR TESSELLATION PATCH
STAR TESSELLATION CODE

Quads are not broadly supported as a basic primitive by modern graphics APIs, so some formats such as glTF don’t currently allow them to be encoded.

STAR TESSELLATION PATCH

When authoring meshes intended for tessellation, it is important to ensure that your asset pipeline does not automatically triangulate your patch geometry.

Some types of modeling are based on subdivision of quads, such as Catmull–Clark subdivision surfaces, which are common in computer-aided design and animated film. Ultimately, tessellation always produces triangles, but you can select between these patch types based on the natural topology of your base geometry. Metal supports two patch types: triangle and quad (short for quadrilateral). With tessellation, you can overcome some of the limitations of vertex attribute storage by generating additional geometry on the GPU at runtime. An example of a highly tessellated planar mesh displaced by a heightmap, resulting in a terrain-like surface Once the geometry is subdivided, you can use techniques like displacement mapping to reposition the refined vertices, creating more detail across the surface, including along silhouette edges. Tessellation allows you to refine your geometry on the fly, without requiring you to allocate additional memory to hold the resulting vertices. Instancing is best used when the repetition of meshes won’t be noticeable, as when rendering debris, foliage, or crowds. Normal mapping does not refine the silhouette edge the mesh, so the effect is not always convincing, but it is a great way to reduce the number of vertices in a mesh.Īnother technique that allows you to get more mileage out of less geometry is instancing, which draws the same mesh multiple times without duplicating the vertex data in memory. One possible approach is to decimate (reduce) the geometry of the mesh while producing a texture map whose texels store fine-grained surface normals.

There are many techniques that can be used to reduce the memory footprint of geometry. If you’ve used Metal to render 3D meshes composed of triangles, you may have encountered a situation where the mesh you wanted to draw was too large to fit into memory. The tessellated triangles then pass through the remainder of the graphics pipeline (vertex shader, rasterizer, etc.) on their way to the framebuffer. The number of triangles generated by a patch is controlled by configuring a fixed-function stage of the pipeline called the tessellator. A patch is a triangular or quadrilateral domain that can be subdivided by the GPU to produce triangles. Conversely, when tessellating, our draw calls are denominated in patches. With ordinary draw calls, we render primitives such as triangles, lines, or points. Tessellation is a form of geometry amplification: programmatically turning geometry into more geometry. Polyhedrons subdivided with Metal tessellation A Brief Introduction to Tessellation

STAR TESSELLATION HOW TO

It consists of a Mac app written in Swift that shows how to dynamically subdivide a cube and icosahedron, optionally smoothing the resulting shapes into approximate spheres.

STAR TESSELLATION CODE

The source code for this article is available here. This article discusses the fundamentals of tessellation and how to do it in Metal future articles will showcase specific use cases. Tessellation is a powerful technique for generating geometry dynamically with many use cases from CAD/CAM to game development and beyond. In this article we will take a look at how to do tessellation on the GPU with Metal.

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