User manual

As visible on Figure 61, the spot light accurately models a projector, in all
respects apart from the rendering of a gobo pattern. However, there is one more
problem: “Light Properties are also used in the Light calculation ... from this table, a
Spot light requires the most calculations ... Lighting calculation is done for each vertex
of the scene and for each light ... Warning: The maximum number of active lights is
limited when using a video card that support Transform and Lighting (T&L). In general
the maximum number of active lights is 8. [31] (Lighting, Shadows and Reflection
Whitepaper)”. Thus, the issue of targeting a particular GPU and its limitations starts
occurring, even in this native case: to use native Virtools spot lights, the graphics card
must support transform & lighting, and even in that case, apart from lack of support of
rendering gobo patterns, there is a maximum limitation of 8 lights.
Looking at NVIDIAs introduction document [24], which also provides an
overview of the capabilities of different generations of graphic cards (presented as
“Evolution of the PC hardware graphics pipeline”), informs us that transform &
lighting (see also [32]) is a technology, that as a GPU feature first gets introduced in
graphic cards from 1999-2000. The transform and lighting unit found on these cards
allows hardware accelerated processing of bump mapping, cube texture mapping and
most important, projective texture mapping.
As Figure 62 demonstrates, projective texture mapping is the necessary
processing function needed to simulate gobo lights.
F
igure 62. Projective Texture Mapping (Ref[24])
"DMX Director" - Architecture of a 3D light-programming application, in a multi-user Internet environment
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