GAMGI Interfaces: Light Modify

# Light Modify

- Geometry
- Color
- Attenuation

Change here the geometry for a single light or a list of lights.

To modify a light, click over the graphic area to open a menu and choose a light, or write its identification (name and number) on the Light entry. To modify a list of lights, press the button List (after creating the list of lights with Light->Select). Parameters for empty entries or Local choices remain unchanged.

To change a light name write the new name in the Light entry, followed by the light number (GAMGI needs the number to identify the light). To change the name for a list of lights, press List first and then write the new common name in the Name entry.

### Directional

Directional lights emulate lights very far from the objects they illuminate (as the Sun illuminating the Earth), so: 1) the light beams can be considered as paralel; 2) the attenuation produced by the distances between the objects is negligible, compared to the attenuation produced by the distance from the source (the intensity of the Sun light iluminating the top of a building or a street nearby is approximately the same).

Directional lights are thus determined by the X, Y, Z coordinates of the Direction vector.

### Positional

Positional lights emit from a single point into all directions, with equal intensity. The attenuation in the beam intensity, from the source to the objects might be already significant (the visibility produced by street lights decreases rapidly with distance).

Positional lights are thus determined by the X, Y, Z coordinates of the light Position.

### Spot

Spot lights differ from positional lights because they emit in a given Direction, as in a lamp. The Angle (beam aperture) between this Direction (the spot) and the light outer limit (the cutoff), can vary between almost 0 degrees (as in a laser) and 90 degrees (as in a ceilling light).

A spot light is thus determined by its position, direction and angle.

Direction, Position, Angle and Attenuation entries are automatically enabled or disabled, according to the type of light selected.
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