GIG reference manual

the lights menu

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Section contents

• Introduction
• Buttons
  • one window
  • flat shaded
  • file
  • get light
  • save light
  • get light tag
  • get solid tag
  • previous
  • next
  • spot coi
  • spot angle
  • spot to tag
  • spot to meter
  • fix event
  • light meter
  • meter to sol
  • local light
  • move
  • add ambient
  • add light
  • add spotlight
  • copy to sol
  • delete
  • cancel
  • cancel all
• Data input boxes
  • tag
  • color
  • color text box
  • x, y and z
  • quadratic/constant/linear
  • no shadow/shadow/soft shadow
  • radius
  • rel. intensity/abs. intensity
  • frame
• Spotlight data input boxes
  • coi
  • angle
  • foc
• submenu
  • color submenu

Introduction
In the lights menu, light sources can be added locally or globally using local light, add light, add ambient, and add spotlight.
Lights can be deleted using delete, cancel and cancel all.
Lights can be saved and restored using save light and get light.
Lights can be copied to the positions of a number of single solids using copy to sol.
Lights can be selected using get light tag, previous and next. Lights can be animated using fix event.
A light meter can be used to measure the relative light intensity of a light
source at a certain position.
Lights can be global (shining on every object in the scene) or local (shining only on the part of the tree to which they are assigned).
Normally lights are global. Local lights can be added using the local light button or using cut, copy, and paste in the view tree menu with edit lights.
Lights have the following properties:

• a 3D position which can be edited using move, x, y, z
  
• a color which can be edited using the color submenu
  
• a tag for easy access
  
• an on/off toggle for shadow casting
  
• a toggle for the intensity loss over distance (quadratic, linear, or constant)
• a radius for creating soft shadows by simulating a light source with a real size (defined by that radius) during shadow calculation when rendering
• an intensity which can be shown in two different ways:
  • As the absolute intensity of the light source. This is the real intensity at the position of the light source and is therefore not of much use because we are normally only interested in the intensity of a light source on a certain object. In the case of quadratic or linear light sources, the intensity of light from a light source falling on an object depends on the distance between the light source and the object, so it is always less than the intensity at the light source itself (the absolute intensity).
    For constant light sources the absolute intensity is always the same as the intensity of light from a light source falling on an object.
  • As the relative intensity of the light source, this is the intensity of light measured at the position of the light meter. This is very useful for measuring the light intensity received by objects in the scene, Place the light meter at the object of which the light intensity received from the current light source is to be measured. The relative intensity box will then show the light intensity at that position in space. Remember that the relative intensity shown depends on the position of the light meter and has no relation with any object in the scene by itself!

Spotlights have the following additional properties:

• a coi which the spot light aims
  
• an angle which determines the size of the spot
  
• a focus which determines the softness of the edge of the spotlight. (0.0 is a hard edge, 1.0 is a soft edge)
  Ambient lights have only these properties:
  
• color
  
• intensity