Class

• <DRM Blend Directional Light>

Superclass

• <DRM Directional Light Behaviour>

Subclass

• None.

Definition

An instance of this DRM class specifies 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 pyramid, subdivided by two planes. These planes are based at the pyramid’s apex and extend towards the base. They subdivide the pyramid into upper and lower sections with a blend section in between. The upper section receives the primary colour, while the lower section receives the secondary colour. The blend section blends between the primary and secondary colours depending on the viewing position.

The upper_plane_angular_offset field specifies the angular offset of the plane separating the upper and blend sections, in radians, from the given <DRM Lobe Data> instance’s LIGHT_DIRECTION vector, measured along its VERTICAL_AXIS vector. The resulting upper section of the light is taken to be between the plane and the positive end of the VERTICAL_AXIS vector.

The lower_plane_angular_offset field specifies the angular offset of the plane separating the lower and blend sections, in radians, from the given <DRM Lobe Data> instance’s LIGHT_DIRECTION vector, measured along its VERTICAL_AXIS vector.

The resulting lower section of the light is taken to be between the plane and the negative end of the VERTICAL_AXIS vector.

Class diagram

Figure 6.22 — DRM_Blend_Directional_Light

Constraints

• Publishable Object

Example(s)

• Consider a <DRM Blend Directional Light> instance with both a primary and a secondary colour.

  

  Figure 6.23 — <DRM Blend Directional Light> example

  At 10 π / 180,0 radians from the LIGHT_DIRECTION vector in the vertical direction, towards the positive end of the vertical axis vector, the primary colour is visible, because the position lies in the upper section of the pyramid, inside the lobe.

  At 10 π / 180,0 radians from the LIGHT_DIRECTION vector in the vertical direction, towards the positive end of the vertical axis vector, the primary colour is visible, because the position lies at the upper edge of the blend section. Moving from this position along the vertical axis vector toward the negative end, the amount of primary colour decreases as it is blended with proportionally increasing amounts of the secondary colour, because this lies within the blend section of the pyramid, from the upper edge to the lower edge. At -0,5 π / 180,0 radians from the LIGHT_DIRECTION vector in the vertical direction (that is, towards the negative direction of the vertical axis), the primary and secondary colours are blended in equal amounts, since this position is in the middle of the blend section. Moving in the same direction, the amount of primary colour continues to decrease proportionally as the amount of secondary colour increases. At -2,5 π / 180,0 radians from the light direction, only the secondary colour is visible, as this is the lower edge of the blend section.

  At -10 π / 180,0 radians from the LIGHT_DIRECTION vector in the vertical direction, that is, towards the negative end of the vertical axis vector, the secondary colour is visible, as this lies in the lower section of the pyramid.

  At -50 π / 180,0 radians from the LIGHT_DIRECTION vector in the vertical direction, that is, towards the negative end of the vertical axis vector, nothing is visible, since this lies outside the pyramid.