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The SEDRIS Data Representation Model
APPENDIX A - Classes Directional Light Behaviour |
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An instance of this DRM class specifies a directional light having a direction and lobe shape defined by a <Lobe Data> component L. The lobe shape parameters are used by subclasses to specify shapes such as cones and pyramids.
The location of the light is specified by the <Location> component. The direction at which the light is pointed is specified by the <Reference Vector> component of L that has a vector_type field value of SE_REFVEC_LIGHT_DIRECTION. The up axis of the light is specified by the <Reference Vector> component of L that has a vector_type field value of SE_REFVEC_VERTICAL_AXIS. The SE_REFVEC_VERTICAL_AXIS vector specifies the rotational orientation of the light around the SE_REFVEC_LIGHT_DIRECTION vector. These provide the necessary information to position the light in the currently applicable SRF, orient the light with respect to its SE_REFVEC_VERTICAL_AXIS vector, and identify the direction in which the light is pointing. The lobe shape is centred horizontally and vertically around the SE_REFVEC_LIGHT_DIRECTION vector, with origin at the location specified by the <Location> component.
Directional lights can have both a primary and a secondary colour. These are specified by the <Colour> components of the parent <Geometry Representation> instance that have colour_mapping values of Primary_Light_Rendering_Behaviour and Secondary_Light_Rendering_Behaviour, respectively.
See concrete subclasses for examples.
This can be done using either a <Cone Directional Light> instance or a <Pyramid Directional Light> instance with primary and secondary colours. Set the horizontal and vertical widths of the lobe to π radians and invisible_behind to SE_TRUE.
No; it does not represent the location of any light(s) that use this behaviour. It is the reference location for the direction of the light (as expressed the <Reference Vector> components of the <Lobe Data>).
In most SRFs, directions shall refer to a location to account for the curvature of the earth. Even in linear space SRFs, localized directions may be important (See Example 1).
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