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All
surfaces must have a material specified in order to determine what the
surface will look like. Materials are based on brushes, so any drawing effect
you can achieve in 2D with a Brush can also be achieved in 3D.
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There
are three styles of brush available, which interact with lighting in
different ways. The DiffuseMaterial works as though the brush had simply been
used to paint the surface with a matte finish. There will be no reflective
highlights when using this brush type. Where directional light sources are
used, the brightness of the surface will be determined by the angle of
incidence of that light source with the surface. (So the brightness will not
vary as the viewer moves around.)
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SpecularMaterial
allows you to get a shiny-looking finish. The brightness is determined not
just by the angle at which directional light hits the surface, but also the
angle from which the viewer is observing.
It will be brightest when these two angles are the same. (If the
surface were flat, this would correspond to looking into a flat mirror at
just the right angle to see the light source reflected in the mirror.)
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EmissiveMaterial
is slightly curious. You would normally apply this to a surface that sits
just above another existing surface. This is because emissive surfaces are
not opaque – they modify whatever is behind them using additive blending. So
an emissive surface can brighten the area of the scene that it covers. If you
use a textured brush such as a DrawingBrush, then the contents of the drawing
will determine the pattern with which this surface brightens whatever is
behind it. This is typically used to get interesting visual effects.
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