Class Name: Blend Directional Light

Superclass - Directional Light Behavior

Definition

A Blend Directional Light is a light whose intensity varies depending on your 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 color while the lower section receives the secondary color. The blend section blends between the primary and secondary colors depending on the viewing position.

Primary Page in DRM Diagram:

• 3

Example

1. The Blend Directional Light has both a primary and a secondary color. The component Lobe Data has horizontal_width = 90 and vertical_width = 90. The upper_plane_angular_offset is 1.5 and the lower_plane_angular_offset is -2.5.

   If my position from the Lobe Data's light direction vector is 10 degrees in the vertical direction towards the positive end of the vertical axis vector (i.e., the Lobe Data's component Reference Vector of type SE_VERTICAL_AXIS), then I see the primary color as I am inside the vertical_width, in the upper section of the cone.

   If my position from the light direction vector is 1.5 degrees in the vertical direction, towards the positive end of the vertical axis vector, then I see the primary color, since I am at the upper edge of the blend section. As I move from here along the vertical axis vector, towards the negative end, the amount of primary color decreases as it is blended with proportionally increasing amounts of the secondary color. This is because I am moving within the blend section of the cone, from the upper edge to the lower edge. Once I reach -0.5 degrees from the light direction in the vertical direction (i.e., towards the negative direction of the vertical axis) I see the primary and secondary colors blended in equal amounts as I am now in the middle of the blend section. As I continue to move in the same direction, the amount of primary color continues to decrease proportionally as the amount of secondary color increases. By the time I reach -2.5 degrees from the light direction, I see only the secondary color, as I have now reached the lower edge of the blend section.

   If my position from the light direction vector is -10 degrees in the vertical direction, i.e. towards the negative end of the vertical axis vector, then I see the secondary color as I am inside the vertical width, in the lower section of the cone.

   If my position from the light direction vector is -50 degrees in the vertical direction, i.e. towards the negative end of the vertical axis vector, then I see nothing, as I am outside the pyramid.

FAQs

Constraints

Composed of (one-way)(inherited)

• one Lobe Data (notes)
• one Location

Component of (one-way)(inherited)

• one or more Light Rendering Properties

Field Elements

Notes

Composed of Notes

Lobe_Data

 lobe shape

Fields Notes

upper_plane_angular_offset

 This value defines the angular offset of the plane that
 lies between the upper and blend sections. It is measured
 in degrees (-180 to 180) from the light direction vector,
 (<Lobe Data> component Reference_Vector of type SE_LIGHT_DIRECTION)
 along its vertical axis vector
 (<Lobe Data> component Reference_Vector of type SE_VERTICAL_AXIS).
 The resulting upper section of the light is taken to be
 between the plane and the positive end of the
 vertical axis vector.

lower_plane_angular_offset

 This value defines the angular offset of the plane that lies between
 the lower and blend sections. It is measured in degrees (-180 to 180)
 from the light_direction vector, 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.