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pauljan

OpenGL Seams on adjacent cubes

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Guest Anonymous Poster
I use z-fighting here to mean something slightly different: parts of a polygon edge showing because that edge is exactly at the same position as the edge of a different polygon.

I obviously misinterpret your remark there, you are talking about lines and polygons not being rasterized 100% the same by OpenGL (showing up when the view angle changes). I think this is known API behaviour, I thought I'd read about it somewhere in the OpenGL specs but I can't really find it atm.

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Guest Anonymous Poster
So, is the application drawing a wireframe to highlight the edges? That image seems to have been compressed and perhaps resized so it's hard to tell much specific from it. I'm also a bit confused about those being cubes. It looks like 16 quads, not cubes, to me. If it just quads then I can only wonder what exactly is suppose to be bleeding through.

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Oh, that's me. I thought it might be worth mentioning one thought. That is that it might be anti-aliasing. You might be blending the edges with that grey background. It doesn't look anti-aliased but then I don't know how close that image is to the original.

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Guest Anonymous Poster
Why do people always have to come up with "I call this xxxxx" - why not stick to generally accepted terminology, or just explain themselves properly?

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No, no, in this case there is no wireframe, and there is no aliasing either (except for the JPG artifacts in the image). And they are cubes, not quads. I just placed the camera in such a way you can't really tell (I wanted the seams to show up clearly).

But truely, I am rather sure this is a completely logical and natural phenomenon given the nature of the geometry. You obviously are not convinced, and I wouldn't mind being proved wrong at all :)

Do you want me to whack up a simple test application to test this in and send it to you? I don't know what your programming language of choice is, and I normally work in Delphi, but it should be easy to fire up some old C/C++ compiler, take one of the most basic Nehe examples and throw in a bunch of cubes.

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Oh, and Mr Anonymous poster back there, the answer is "because they don't know any better". I didn't know the term z-fighting was reserved for coplanar primitives only. If you leave that single word out, the following definition applies nicely:

"Z-fighting is a phenomenon in 3D rendering which occurs when two or more coplanar primitives have the similar values in the Z buffer (usually caused by floating point round-off errors), causing random parts of the primitives to be rendered"

Sorry for being a bit ignorant, I am trying to learn :)

(also, blame Wikipedia for the typo, not me)

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