Afternoon, n.:
That part of the day we spend worrying about how
we wasted the morning.

Concept 7.2 : Light Position - Stationary Lighting
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Idea:
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A light source is subject to the same matrix 
transformations as a primitve.  
By changing the location in the program at which the
light position is set we can achieve different effects.

Stationary Lighting
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To keep the light fixed set its position after any
viewing and or modelling transformations.

In the above code fragment, we define the light position
after setting our view point.  Hence when we look at the
back of the cube it appears unlit.