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Clipping Issues: Impossible To Fix?
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Posts: 41


Tue, Sep 11 2012

This has been one of my biggest problems with NinevehGL, an issue when two polygons are too close together. When this happens, very ugly clipping occurs. In this example screenshot below, the table to the top of the image is one .obj model. The table underneath this one has a tablecloth model positioned and oriented ontop of the table model itself. Both of these models are only comprised of quads, and none of these polygons are intersecting each other. The table cloth's polygons have been modeled in such a way to ensure that the cloth encompasses the table and that no polygons are overlapping. Yet still, the render looks... hideous.

I have tried playing with the contentScaleFactor setting and this only seems to affect antialiasing and texture quality. None of the other global quality settings seem to affect the outcome either.

Here is a screenshot of what I was describing above:

Is there any possible way to overcome this issue / will there be an improved rendering system in further versions of NinevehGL that will resolve this? Everything else about NinevehGL is fantastic, but when it comes down to it Nineveh is supposed to be a rendering engine at heart and it seems if the renders look as bad as this then that should be fixed first and foremost...

Thank you for any input possible,
- Adam Eisfeld
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Posts: 571


Tue, Sep 11 2012

In response to: @adameisfeld

Hello Adam,

Well, this is not a NinevehGL behavior... it's more related to OpenGL behavior. This issue is also known as "Z fighting". To solve that OpenGL offers functions like "glPolygonOffset".

You can use this function without problem, anywhere in NinevehGL.

But it's also true that NinevehGL should offers an easy way to deal with this problem.
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Posts: 41


Tue, Sep 11 2012

In response to: @dineybomfim

Thanks Diney,

In searching for examples of using the glPolygonOffset routine and attempting to incorporate it with no results, I stumbled across a forum post that mentioned setting the camera's near plane to a larger value will fix this issue as long as the polygons aren't coincident (intersecting). As this was my case, I decided to test it out, and set me camera's nearPlane to 0.05. What do you know, it worked! No clipping or z-fighting occurs until the camera is well away from the object, which is fine for my purposes.

I will experiment with different near plane values, but for the time being 0.05 seems to have worked perfectly for my needs.

Thanks again Diney, and keep up the great work on Nineveh. I hope it is still under development as it is an amazingly useful engine and I'm sure I speak for everyone when I say we all are very excited for getting some of the features listed on the road map!

- Adam Eisfeld
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Posts: 571


Wed, Sep 12 2012

In response to: @adameisfeld

Hey Adam,

Sure we still in development! We're a little late, but no big deal.

BTW, yes, there are some workarounds, anyway, this could be a necessary option to dealing with.

Good luck! And keep providing us your nice feedback.
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