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Inside Multimedia 1995 December
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grafik
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povhelp
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layered.hlp
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It is possible to create a variety of special effects using layered tex-
tures. A layered texture is one where several textures that are partially
transparent are laid one on top of the other to create a more complex tex-
ture. The different texture layers show through the transparent portions to
create the appearance of one texture that is a combination of several textu-
res.
You create layered textures by listing two or more textures one right af-
ter the other. The last texture listed will be the top layer, the first one
listed will be the bottom layer. All textures in a layered texture other
than the bottom layer should have some transparency. For example:
object {
My_Object
texture { T1 } // the bottom layer
texture { T2 } // a semi-transparent layer
texture { T3 } // the top semi-transparent layer
}
In this example T2 shows only where T3 is transparent and T1 shows only
where T2 and T3 are transparent.
The color of underlying layers is filtered by upper layers but the re-
sults do not look exactly like a series of transparent surfaces. If you had
a stack of surfaces with the textures applied to each, the light would be
filtered twice: once on the way in as the lower layers are illuminated by
filtered light and once on the way out. Layered textures do not filter the
illumination on the way in. Other parts of the lighting calculations work
differently as well. The result look great and allow for fantastic looking
textures but they are simply different from multiple surfaces. See STONES
.INC in the standard include files for some magnificent layered textures.
NOTE: Layered textures must use the "texture{...}" wrapped around any
pigment, normal or finish statements. Do not use multiple pigment, normal
or finish statements without putting them inside the texture statement.
Layered textures may be declared. For example:
#declare Layered_Examp =
texture { T1 }
texture { T2 }
texture { T3 }
Then invoke it as follows:
object {
My_Object
texture {
Layer_Examp
// Any pigment, normal or finish here
// modifies the bottom layer only.
}
}