Graphics know-how
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ELSA GLADIAC
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24
EN
쎲 Transformation – In transformation, the objects are aligned in
perspective as seen from the observer's point of view.
쎲 3D clipping – In this process, each polygon is checked to determine
whether it is partially or fully invisible. The invisible faces or parts of
objects will be removed.
쎲 Back face culling – This process computes hidden surfaces resulting
from the observation perspective chosen. Any object having an invisible
front surface is omitted.
쎲 Illumination – The illumination of the scene by different light sources is
calculated.
쎲 Scaling on the screen – The above steps are now calculated for three-
dimensional space using normalized coordinates. The on-screen image
coordinates will only now be computed.
Rendering
At this stage, the 3D scene is filled with color shades and textures are
applied. Different processes and methods are also applied here.
쎲 Shading – Shading takes account of the effects created by different light
sources on the 3D object and provide for a very realistic overall
impression. Here, too, there are different methods which are more or
less processor-intensive:
쑗 Flat shading assigns a color value to each polygon. This results in a
faceted representation, which requires only short computation times.
쑗 In Gouraud shading, all the vertices of the polygons are assigned a
color value. The remaining pixel information for the polygon is
interpolated. This method gives a very gentle color transition, even
with fewer polygons than are required for flat shading.
쎲 Texture mapping – At this stage, the 3D object undergoes a sort of
”face lift”. The materials and textures are assigned. Different methods
are used here to make the textures appear realistic, even when enlarged
or reduced. As a first step, the textures are computed:
쑗 Point sampling is the simplest method. A pixel-by-pixel comparison
is made between the texture template and the surface to be filled.
This method leads to a very coarse representation, especially when
enlarged.
쑗 In linear mapping, a new color value is interpolated from the adjacent
pixels (or texels) of a texture. This gives better results than point
sampling, as the hard boundary between the coarse pixels is blurred.
21663_DE_0300.book Seite 24 Montag, 10. April 2000 12:22 12
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