misc.txt

download original
(beware -- all obsolete these days, use shaders instead)

- lighting enabled globally via glEnable(GL_LIGHTING) (needed to be
  called only once)

- up to 8 light sources, GL_LIGHT0 ... GL_LIGHT7 (??)

  - enabled separately via glEnabled(GL_LIGHT[0..7])

- 3 kinds of things light properties are applied to:

  - per - light source properties, set via glLight*

    - examples of such properties:

      - ambient, diffuse, specular color of the light

      - position of the light

        - specified as (x,y,z,w)

        - with w=0: directional light (infinitely far away)

        - multiplied with the modelview matrix that's in effect at the
          time of the glLight* call to give the position in eye
          coordinates, which is the one that's saved

          - thus, to get a light that's positioned relative to the
            camera rather than somewhere in the world cosy (i.e.,
            moves with the viewer), set the position immediately after
            glLoadIdentity() of the modelview matrix, before setting
            any object->world or world->camera transformations

      - constant, linear and quadratic attenuation factors

        - ...ultimate intensity of a vertex at distance D from the
          light will be determined as 1/(fC + fL*D + fQ*D^2) (plus
          spot directions...)

      - if the light is a spotlight, rather than one that's shining in
        all directions: spot direction, cone angle ("cutoff angle"),
        spot exponent (attenuation as you get farther away from the
        center line of the cone)

  - per - object light properties ("material properties"), set via
    glMaterial* or glColor* + glColorMaterial

    - ambient, diffuse, specular, emissive color of the material

       - ambient and diffuse normally the same

       - ambient = global backlight affecting all surfaces euqally

       - diffuse = diffuse reflection, i.e. surface color/brightness
         depends on the angle of the surface normal relative to the
         light direction, but not on the viewing direction

       - specular = directed reflection, i.e. light "bounces off" in a
         specific direction (with incoming = outgoing angles), so the
         location of the viewer also determines the seen color

       - ambient and diffuse color should normally be the same

    - specular exponent ("shininess")

      - value between 0.0 and 128.0...

    - seen color caused by lighting is always calculated for the
      vertices of a polygon only and then interpolated in between, so
      for more realistic lighting, the polygons have to be
      comparatively small

    - as a basic rule, the R,G,B components of the seen color are
      obtained by multiplying the respective component of the light
      witht that of the material. (this if of course done for all
      light sources and types of light as well as for the global
      ambient light, and the results are properly rescaled and added)

    - properties may be specified separately for the front and back
      sides of the polygons

    - rather than using glMaterial* to set all these parameters
      separately, you can also use glColor* to set them, provided you
      previously used glColorMaterial to specifiy which of the above
      property the glColor should apply to. This is useful if you want
      to change just one property very often when drawing vertices.

  - global light properties, set via glLightModel*

    - global ambient light color

    - whether or not the viewer's position is accounted for when
      calculating specular reflection angles...

    - whether both sides or just the front sides of polygons should be
      shaded correctly (many times, all back sides are insivisible, in
      which case it is faster to not have to consider them)

    - whether specular color is calculated separately from ambient and
      diffuse
back to lighting