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MrSparkle27

OpenGL Optimizing the triangulation

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Hi! I implemented the Cutting-Ear-Algorithm to triangulate any convex or concave polygon. The result is pretty good but sometimes there are some very thin triangles due to how the algorithm works. Is it recommended to optimize the triangulation or doesn't it really matters when rendering with DirectX or OpenGL? Which would be the best way to optimize the triangulation? Currently I try to compare the bounding circles of all adjoining triangles. If a triangule is completely in a bounding circle of another triangle I swap the segment between both triangles. This works pretty good but is much slower than the triangulation itself, and I'm still not sure if it's really worth it. Christian

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This is the result so far, it creates a nice triangulation but it's still very slow at the moment. As you can see the long, thin triangles are replaced. I'm not sure if this is really appropriate.

Before optimization:


After optimization:


[Edited by - MrSparkle27 on July 28, 2008 2:20:53 PM]

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Do you want to do this real-time? If not, there will of course be no harm in trying to reduce the amount of triangles while preserving the shape. But if you are doing it real-time, it will be hard to cut out a few extra triangles and render it faster than it will be to just render it all.

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Nope, I don't want to reduce the number of triangles. I just want to optimize the shape of the triangles.

The Cutting Ear algorithm can produce very thin triangles but I'm not sure if this could affect the output when rendering the mesh with DirectX or OpenGL.

In a 3d modelling program like 3ds max, it's always best to optimize the triangulation of the meshes to avoid ugly artefacts during rendering.

My question is wether it is recommended to optimize the triangulation or just waste of time.

Thanks,
Christian

PS: How can I include images to my postings?

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As long as you do flat-shading, it is probably no gain in optimizing it. But as soon as you do any pr. vertex normal stuff, I believe long narrow triangles will give you artifacts.

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Yes, you may be right. I also thought about texture coordinates. I guess the interpolation of the uv coordinates along the long edges can result in really ugly distortion of the textures. Maybe it's really worth to implement a mesh optimizer though.

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This smells like a classic case of optimising before you need to. Have you benchmarked the original method? Have you actually seen artifacts caused by the first? If not, no need to optimise.

Also, if you intend to do this at run time, it's more likely that you don't need to retessellate each frame, just cache the geometry somewhere. Do you intend to have this work with shapes that have holes?

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Hi! Thank you for your comment. No, I haven't actually seen some artefacts, but I know that most 3d applications have problems with unoptimized triangles, especially when interpolating texture coordinates along the edges of these long, thin triangles. I don't want to optimize the triangles every frames but every time the mesh has been changed by the user.

Currently I implemented a very simple algorithm for testing issues, but it's still very slow. Basically it works by testing all adjoining triangles if it's possible to swap the diagonal in order to minimize the length of the sides of both triangles. It produces a nice triangle net but still has some performance issues I want to overcome at some time. If anyone knows an algorithm that is already existing, please let me know.

Christian

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If you are interested in doing great quad meshes, here is a paper that looks interesting : http://www.graphics.rwth-aachen.de/uploads/media/spm08.pdf

About triangle, you should take a look at that paper : http://www.graphics.rwth-aachen.de/uploads/media/automatic_restoration.pdf
I haven't read it but it looks interesting !

EDIT : this one too : http://cit.zesoi.fer.hr/downloadPaper.php?paper=270

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