Class Name: Blend Directional Light

Superclass - <Directional Light Behaviour>

Subclasses

Definition

An instance of this DRM class specifies a <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.

Primary Page in DRM Diagram:

• 21

Secondary Pages in DRM Diagram:

Example

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

   

   At 10 π / 180.0 radians from the SE_REF_VEC_TYP_LIGHT_DIRECTION vector in the vertical direction, towards the positive end of the SE_REF_VEC_TYP_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 SE_REF_VEC_TYP_LIGHT_DIRECTION vector in the vertical direction, towards the positive end of the SE_REF_VEC_TYP_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 SE_REF_VEC_TYP_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 SE_REF_VEC_TYP_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 SE_REF_VEC_TYP_LIGHT_DIRECTION vector in the vertical direction, that is, towards the negative end of the SE_REF_VEC_TYP_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 SE_REF_VEC_TYP_LIGHT_DIRECTION vector in the vertical direction, that is, towards the negative end of the SE_REF_VEC_TYP_VERTICAL_AXIS vector, nothing is visible, since this lies outside the pyramid.

FAQs

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Constraints

• <<Publishable Object>>

Composed of (two-way) (inherited)

• one <Lobe Data> instance (notes)
• one <Location> instance

Component of (two-way) (inherited)

• one or more <Light Rendering Properties> instances

Inherited Field Elements

Field Elements

Notes

Composed of Notes

Lobe_Data

 This specifies the lobe shape.

Fields Notes

upper_plane_angular_offset

 The upper_plane_angular_offset field specifies the angular offset
 of the plane separating the upper and blend sections, in radians,
 from the given <Lobe Data> instance's SE_REF_VEC_TYP_LIGHT_DIRECTION
 vector, measured along its SE_REF_VEC_TYP_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
 SE_REF_VEC_TYP_VERTICAL_AXIS vector.

lower_plane_angular_offset

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

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