Roof Z-Fighting

[lbuttery]

Any ideas why I'm getting Z-fighting for my roofs ???

Lew

[Tommy Blair]

Not really. I don't think I've had that problem with roofs. Sorry. I think this is the second time I've seen a thread on this today.

[lbuttery]

second time I've seen a thread on this today.
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Tommy:

I did also and my reply was that maybe the house height was out of sync with the roof ???


I checked mine and rebuilt the roof and it's still there ???

Lew

[Allen42acj]

Lew
What version are you using?
Can you post the plan or send it to me?
I had that before and fixed but don't remember how.

[lbuttery]

Allen:

Why my version



It's gone now ???


thanks anyways


Lew

[Allen42acj]

Maybe that's how I had fixed..

[Doug Park]

OpenGL uses a class of algorithms that employ what is known as a Z buffer. The Z buffer is a finite number of layers that represent all the distances from the front clipping plane to the back clipping plane of the model.

Think of it as the thin slices of meat that you get at the deli or slices of bread.

Since there are a fixed number of slices (32K for most video cards) proper tuning of the thickness of each slice is important. Normally we calculate a front and back clipping plane that works well. However, when you move the camera very far away from the model as in the above case occasionally that calculation doesn't work real well.

Moving the front clipping plane further away from the eye point of the camera will put more slices into the area where your model is and should correct the z-fighting. Normally the front clipping plane will be about 24" out. Setting it to about 10' or so in your example should correct the issue.

[lbuttery]

Doug:

thanks for the clarification

Lew

[sherpa_jones]

Can someone clarify for me what Z-fighting is? I'm sure it has nothing to do with the UFC, but that is all I am certain of.

[Allen42acj]

Hi Rod
I believe it is when you see two materials in the same place..
Might have something to do with UFOs

[RMorrison]

I've also been able to correct this by thickening the roof material in the Roof Surface area under the Options tab in the Roof DBX.

[lbuttery]

Richard:

I'm curious why the default roof material wouldn't be "thick" enough ???

Is this something CA needs to address ???


Lew

[Doug Park]

We create the materials with real world thicknesses. So they are by definition thick enough. There are a finite number of slices available and so when the model space gets large enough surfaces are to machine precision in the same place. When this happens computationally one surface or the other will compute to be in front depending on the pixel location.

This results in some pixels of the surface behind bleeding through. That result is called z-fighting.

There are several things that can be done to deal with this.

One is as I suggested, moving the front clipping plane forward. Another would be to remove the surfaces that are obscured. For example, we could have a mode where we only display the outside and inside surfaces of a wall or roof. However, it is usually better to draw everything for typical models.

There are 65K slices on most video cards. I know I said 32K above, but I was thinking about the size of a signed 16 bit value rather than the unsigned value. This means that if surfaces are 1/16 of an inch apart you could stack 65K faces 1/16" apart resulting in something like 341 ft in model space. For most wall and roof materials the distance apart is more like 1/2" which means you would have 2730 ft of model space to work in.

There are clearly some things we will need to deal with in the long run to deal with city sized models, but for now simple solutions like moving the front clipping plane forward are much easier to deal with.