Does mist help?

I’ll get right to the point.
First of all, does the game engine only render what is being seen by the camera and if so does mist help with frame rate?

I’ll also get right to the right.
The game engine renders all that the objects in the active scene. The only thing mist does is make it look pretty. If anything, mist would make it render a bit slower.

The gameengine renders all objects that are in contact with the camera frustum. An automatic culling prevents all objects outside of the rustum to be rendered. This is only for render not physic and logic. The frustum is defined by the camera paremeters (start,end, lens).
-> Mist has no influence on the object culling.

Pixels outside of the frustum are rendered (computed) but not displayed as they do not fit into the Z-Buffer. This has the effect that faces to near to the camera are cut and you can look inside an object. Faces to far away from the camera are cut as well and you can see the background of the scene.
-> Mist reduses the cutting of the far away faces. It provides a “smooth” transition to the end of the frustum by blending the background color over the pixels depending on the distance.

There shouldn’t be a big difference on the performance when mist is on or off.

I thought that frustum was just there to frustrate you.

The problem with mist is that it makes all your Add-rendered objects reveal their actual geometry when viewed from a distance. That is, if you have a lamppost that has a plane around it supplying glow, at a distance you will see a square over the post.

Yeah I hate that, guess you have to take the bad with the good.

I started using only alpha maps to get past this. It does’nt look quite as good but it gets the job done.

Why does this happen, anyway?

yea, a couple of quick alphas on a stationary camera does a nice job sometimes .