12/3/2023 0 Comments Triangle tessellation 128x128The number of vertices per patch can be defined on the application-level using: A patch primitive is a general-purpose primitive, where every n vertices is a new patch primitive. Tessellation stages operate on patches, a primitive type denoted by the constant GL_PATCHES. The Tessellation Evaluation Shader (TES) takes the tessellated patch and computes the vertex values for each generated vertex. The tessellation primitive generator takes the input patch and subdivides it based on values computed by the TCS or provided as defaults. The TCS is optional default tessellation values can be used if no TCS is provided. Without this protection, gaps and breaks in what are supposed to be contiguous patches can occur. So if you have two adjacent patches that need to have different levels of tessellation, the TCS invocations for the different patches need to use their tessellation controls to ensure that the shared edge(s) between the patches use the same level of tessellation. Therefore, the TCS is primarily responsible for ensuring continuity across patches. The Tessellation Control Shader (TCS) determines how much tessellation to do (it can also adjust the actual patch data, as well as feed additional patch data to later stages). Each stage of the tessellation pipeline performs part of this process. Generally, the process of tessellation involves subdividing a patch of some type, then computing new vertex values (position, color, texture coordinates, etc.) for each of the vertices generated by this process. They are described below, in the order they are processed. Two of the stages are programmable between them is a fixed function stage. The tessellation process is divided into three stages which form an optional part of Vertex Processing in the rendering pipeline. It's not going to interactively change your model, and you can't use the history once you've cut this thing into triangles - but maybe it's a start.Note: This describes the OpenGL 4.0 feature, not the old gluTess* tessellation functionality. Change the tessellation of the NURBS object, then duplicate the polygon and do the same thing. So this is the basis of the construction - leave this polygon alone, duplicate it, then extract half the faces to get two equilateral triangles made up of equilateral triangles. If you go back to your NURBS surface, you can adjust the "Number U" and "Number V" in the Tessellation attributes, and your polygon surface will change with it because of the historical connection between the two. You'll get a polygon parallelogram consisting of 18 equilateral triangular faces. In the options box, check "Match Render Tessellation" and click "apply". Select the surface, go to "Modify -> Convert Nurbs to Polygons" and select the options box. If your triangles are not equilateral, go to the Edit Nurbs menu and reverse either the U or the V direction of the surface, and the tessellation will change. When you do this, you should see 18 equilateral triangles. NOTE: The Tessellation Display is not supported in Viewport 2.0 you'll see something but it will be WRONG! Switch your hardware renderer to the Legacy Viewport. Under the "Primary Tessellation Attributes", make sure that the Mode U and Mode V are set to "Per Span # of Isoparms", and set the number to the same in both U and V (my illustration uses 3). In the Attribute Editor for this surface, open up the "Tesselation" rollout, and check the box marked "Enable Advanced Tessellation". I duplicated the curve, moved it 5 units in X and lofted the two curves together. There are a few ways to do this - I created an EP curve by snapping one EP at the center of the grid, then snapping another 5 units up on the Y axis then I rotated that curve 30 degrees in Z. This is essentially two equilateral triangles in one surface. Not sure if this will help you - but try this - (it's a little kludgy and not really ready for prime-time, but interesting - and maybe you can derive a script from it).Ĭreate an equilateral parallelogram in NURBS with an angles of 60 and 120 degrees on opposite corners. You can get this kind of triangular tessellation in NURBS geometry, but the geometry has to be four-sided.
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