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Fog

Adding fog to your world has more than one purpose. Besides trying to give the player the impression of actual fog, it can be used to obscure objects in the distance and have them gradually become clearer as the player gets closer. This is beneficial both in allowing you to reduce the number of geometry on the screen at one time (thus improving performance) and in preventing objects from suddenly popping into the view frustum.

There is more than one way to impement fog, but because OpenGL has a built in solution we will simply use that.

OpenGL Fog

OpenGL's built-in fog support works by blending each pixel with the color of the fog, using a blend factor dependent on the distance from the viewer, the density of the god and the currently selected fog mode.

To use fog, you must first enable it:

GL.Enable(EnableCaps.Fog);

Fog has several paramaters associated with it, which you can control with calls to GL.Fog

void GL.Fog(FogParameter, int);
void GL.Fog(FogParameter, float);
void GL.Fog(FogParameter, float[])

The values of the GL.Fog(FogParameter) enumeration are:

  • FogMode This parameter specifies which blend equasion to use when caluclating fog. By default it's Exp. It can be set to:
    • (int)FogMode.Linear
    • (int)FogMode.Exp
    • (int FogMode.Exp2
  • FogDensity This parameter is a single value, representing the density of the fog. The default value is 1.0
  • FogStart A single float, representing how far from the near plane the fog should start
  • FogEnd A single float, representing how far from the near plane the fog should end
  • FogIndex Specifies the color index to be used in 8-bit color mode
    • Don't bother, we don't use this!
  • FogColor This specifies the color to be used for fog. It's an array, RGBA
  • FogCoordSrc We don't touch this. It specifies the depth term of the fog blend equation. This is an extension, and is not always available.

That's all there is to fog. Because modern computers can handle far planes that are insanley far away (1000 to 5000) we tend to not use fog to hide things, we only tend to use it as an environmental effect when appropriate.

Because you will likeley not need to use fog (I've NEVER used it) we're not going to do an exercise on it. Just know that you have to first enable it, then you can set paramaters if the default fog doesn't look good.