User manual

utilising hardware acceleration of the GPU is a necessity for a custom texture drawing
of gobos).
In this case, as well as when using a spot light model, there are no visible light
cones “in the air” coming out from the projectors – only the light effects are rendered
on the mesh materials. Since these cones can be seen as visual aid during light
programming, they are simulated - that is handled by creating actual geometric 3D
cone models, with dimensions approximating the expected physical set-up situation.
As the light cones end up being actual conical 3D models, the dependence of the
applied TexGen algorithm solely on the size of the referential object for rendering the
eventual reflection output, actually allows a more-less accurate approximation of the
gobo reflections - provided that the dimensions of light cones are calculated to
simulate the actual projector set-up, and it is them acting as referential objects for the
pattern reflections. The problem of faces in the shadow being wrongly lit, can be
handled by separating the lit object (in this case, the chimney tower) into constituent
face objects, and running a rough ray-tracing algorithm to determine which of them
should reflect a given gobo; those that pass the test get a light material added as a
channel, and compositing can occur on the hardware level as described previously.
This is the base of the solution of the projector light simulation in the current
version of the user site. In essence, it tries to satisfy the real-time demands of the cue
playback engine, by using light materials, added as channels to the mesh of the lit
surface, that refer to one projector (and the gobo pattern thereof) each. The reference
objects are in fact the projector light cone models, with dimensions calculated to
reflect the physical projector setup; the corresponding gobo pattern is a planar
reflection of their bounding box, calculated on the hardware level by the GPU (due
usage of a TexGen effect in the light materials). Thus, the cue playback engine can
settle with applying corresponding rotations to all light cone objects each render
frame, which is possible to be performed on a Virtools scripting level in real-time; all
the corresponding calculations of the gobo reflections, including colours, rotations
and compositing, are passed on to the GPU for that render frame. Let’s just mention
that the cue playback engine, when applying colour, applies it both to the material of a
light cone, and to the light material that renders the reflection pattern on the lit object.
By choosing a solution that incorporates material TexGen effects, we again
incorporate a GPU feature: “TexGen (Texture Coordinates Generators) are Fixed-
"DMX Director" - Architecture of a 3D light-programming application, in a multi-user Internet environment
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