Class

• <DRM Cone Directional Light>

Superclass

• <DRM Directional Light Behaviour>

Subclass

• None.

Definition

An instance of this DRM class is a <DRM Directional Light Behaviour>, the intensity of which varies depending on the observer's position relative to the light's location, direction, and shape. This light takes the shape of a cone, which can be elliptical.

A <DRM Cone Directional Light> instance can specify a plane that divides the light cone into an upper and a lower section along the body of the cone. The upper section receives the primary colour while the lower section receives the secondary colour, if one is used.

Class diagram

Figure 6.49 — DRM_Cone_Directional_Light

Constraints

• Publishable Object

Example(s)

• A 100 kilometre highway has regularly spaced lampposts. Each lamp has <DRM Cone Directional Light> with <DRM Lobe Data> pointing down. If all the lamps use the same <DRM Cone Directional Light>, instance, then all the directions will be parallel. Due to the curvature of the Earth, very few of the lights will shine directly down; the others will be slightly skewed. If, instead, the set of lamps is divided into smaller contiguous groups, each with its own <DRM Cone Directional Light> instance using a <DRM Location> near the centre of the group, the skewing effect will be greatly minimized.

• Consider a <DRM Cone Directional Light> instance with a primary colour that is a <DRM Colour Index> with intensity_level = 0.8.

  

  Figure 6.50 — <DRM Cone Directional Light> example

  equation:
  final_intensity = minimum_colour_intensity + ((((width / 2,0) - degrees_away_from_direction_vector) / (width / 2,0)) * (full_intensity - minimum_colour_intensity))

  At 15 degrees from the light direction vector in the horizontal direction, the final intensity is 0,35.

  At 25 degrees from the light direction vector in the horizontal direction, the final_intensity is 0,2, because that position lies outside the horizontal width of the lobe.

• Consider the following <DRM Cone Directional Light> instance, with its primary colour specified by an <DRM Inline Colour>, so that the full intensity is 1,0.

  

  Figure 6.51 — <DRM Cone Directional Light> example

  At 40 degrees from the light direction vector in the horizontal direction, the final_intensity is 1,0, because use_full_intensity is TRUE and the position lies inside the horizontal width of the lobe.

  At 50 degrees from the light direction vector in the horizontal direction, the final_intensity is 0,5, because the position is outside the horizontal width.

• Consider a <DRM Cone Directional Light> instance with both a primary and a secondary colour, each of which is a <DRM Colour Index> instance with intensity 0,8

  

  Figure 6.52 — <DRM Cone Directional Light> example

  At 40 degrees from the light direction vector in the vertical direction, the primary colour is in effect with intensity 0,8, because the position is inside the vertical width and use_full_intensity is TRUE.

  At 40 degrees from the light direction vector in the horizontal direction, the secondary colour is in effect with intensity 0,8, because the position is outside the horizontal width and minimum_colour_intensity = 0,0.

• Consider a <DRM Cone Directional Light> instance with both a primary and a secondary colour, each of which is a <DRM Colour Index> instance with intensity 0,8,

  

  Figure 6.53 — <DRM Cone Directional Light> example

  At 25 degrees from the light direction vector in the vertical direction, towards the positive end of the vertical axis vector, the full intensity of the primary colour is 0.8, because this position lies in the upper section of the cone and the minimum_colour_intensity is 0,0.

  At 15 degrees from the light direction vector in the vertical direction, towards the positive end of the vertical axis vector, the full intensity of the secondary colour is 0,8, because this position lies in the lower section of the cone and the minimum_colour_intensity is 0,0.