World Lights and Fog
The Directional Light
The directional light in the world is the light source that shines in a particular direction. It is used to approximate the light coming from an extremely distant light source, such as the sun. Generally speaking, polygons facing the directional light source will appear brighter than polygons facing away from it, although this does depend on the surface properties set for a particular polygon. Both the color and the direction of the directional light source can be adjusted.
To change the color of the directional light source, you can either enter a new RGB value directly into the Red, Green, and Blue component fields, or you can click on the Picker... button to bring up a color picking dialog where you can interactively change the color. To disable the directional light source, simply set its color to black (i.e. set the red, green, and blue components to zero).
The direction of the light source is determined by the X, Y, and Z components of a vector. If you are not familiar with vectors this may be a little difficult to visualize at first. Simply put, the three components of the vector adjust to what degree the light points in each of three directions. The X component determines how much the light faces in the east/west direction, with positive values facing west. Similarly, the Z component determines how much the light faces in the north/south direction, with positive values facing north. Finally, the Y component determines how much the light faces in the up/down direction, with positive values facing up. Since directional lights typially shine "down" from "above", the Y component will usually be negative. Making the Y component positive will create a light that appears to shine up from below.
For example, the following settings will create a directional light source that shines down at a 45 degree angle from the southwest corner of the sky:
The Ambient Light
The ambient light is a light source that shines on all polygons equally from all directions. The exact degree to which the ambient light shines on a particular polygon is determined by that polygon's ambient surface property. Since the ambient light is directionless by definition, only the color of the ambient light can be adjusted.
To change the color of the ambient light source, you can either enter a new RGB value directly into the RGB component fields, or you can click on the Picker... button to bring up a color picking dialog where you can interactively change the color. To disable the ambient light source, simply set its color to black (i.e. set the red, green, and blue components to zero).
Fog is a rendering effect that causes objects to become less and less visible as they recede into the distance, until ultimately they become invisible. It is sometimes used to hide the fact that you can't see objects beyond a certain distance anyway.
When enabled, fog has two parameters: the distance from the camera at which fog begins (the "minimum" distance) and the distance from the camera at which the fog effect reaches 100% (the "maximum" distance). Any objects that are beyond the maximum fog distance from the viewer are completely obscured and cannot be seen.
Fog also has a "color" in the sense that as objects get further from the viewer they all begin to approach a uniform color. Fog in Active Worlds uses the current backdrop color as set in the World Features dialog.
Usually the fog effect works best if there is no backdrop image in the world (as set from the World Features dialog), so if you want to turn fog on in your world, be sure to remove the backdrop image as well. However there may be cases where subtle combinations of both fog and a backdrop image can be used to achieve certain effects.