Texture/model flickering in distance (3D)

Question

Ok, in my XNA project i've added simple shader + model loading code, anything works. I created a very simple low-detailed model in 3Ds Max. Exported and imported to XNA with FBX format.

The problem is: if i move my simple camera to some distance from this model, one of its components starts to flicker. I tried another model and there is the same situation, some of components start to flicker and only if i get to some distance from model.

This flickering (or blinking or ..) appears only with textured objects (probably), and looks like: in each frame random parts/pixels of model (or not so random) replaced with object which is behind a model or its component... :(

UPDATE: Now i know - problem is in my model (i checked some other models). I dont understand why but Plane object gives that flickering. Maybe the problem is not in Plane object.

Answer 1

This is only an educated guess but: Your far-plane is too far away, or your near-plane is too close, or both.

A perspective camera gives you a viewable area that looks like this:

Your Z-buffer (depth buffer) covers the range between the near and the far planes. A typical Z-buffer might have 24-bits of precision, giving you 2 ²⁴ possible values. The further apart your near and far planes are, the greater the world-space distance each possible value must covers. In other words: your Z buffer is less accurate.

What you are seeing is known as " Z-fighting " . This is where the Z-buffer is not accurate enough to differentiate between the depths of two given pixels. So you end up with pixels that should have been rejected as being "behind" what was already rendered, drawn instead.

(Alternately your model has some coplanar or nearly coplanar triangles - that is triangles who's surfaces are too close together. Same issue: Not enough precision in the Z-buffer to differentiate between the two surfaces.)

You may also wish to enable backface-culling ( RasterizerState.CullCounterClockwise ), if it is not already enabled. This culls triangles facing away from the camera, removing one possible source of Z-fighting.

Answer 2

I have seen this happen before on models where there are two or more surfaces overlapping in the same plane, one surface is inside the other but in the same plane - so the system can not tell which surface is in front of the other and usually ends up with a mash-up of both surfaces.

It looks like you have a smaller rectangular surface intersecting with a larger rectangular surface that makes up the lower base shape of your model. Probably from another object inside the box? Or from a object subtraction error that left two rectangles inside each other on that surface maybe? Either way modify the model so there are no longer two surfaces with in each other.