The nice feature of our system is that effects can be attached to various types of objects, not just shapes. For example a particular light source may have a shader effect assigned. This allows to modify the contribution of a given light. For example the spot light shape can be modified, possibly based on some texture information (see Figure 5.3, “Textured spot light with shadow”). Or a different lighting model may be implemented, like anisotropic Ward or Cook-Torrance. To make this possible, the effects field is added to every light node:

X3DLightNode

MFNode [] effects [] # Effect

Figure 5.3. Textured spot light with shadow

An example below demonstrates how light effects are specified inside an X3D. The code makes a spot light with an exponential drop-off, similar to traditional OpenGL fixed-function spot lights. Such code can replace (or multiply with) the standard X3D concept of the linear drop-off for spot lights.

The customization is done by overriding the PLUG_light_scale. Remember that all plugs available in our implementation are documented in Appendix A, Reference of available plugs.

SpotLight {
  effects Effect { language "GLSL"
    parts EffectPart { type "FRAGMENT"
      url "data:text/plain,
        uniform vec3 castle_LightSource0SpotDirection;

        void PLUG_light_scale(inout float light_scale,
          const in vec3 normal_eye,
          const in vec3 light_dir)
        {
          light_scale *= pow(dot(normalize(
            castle_LightSource0SpotDirection), -light_dir), 10.0) * 2.0;
        }"
    } } }