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ELSA ERAZOR II and ELSA VICTORY Erazor LT
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Geometrical transformation
This part of the 3D pipeline is very processor-intensive, as all the calculations for the 3D
scene are carried out at this stage. Described in simple terms, it comprises the following
steps:
Illumination–The illumination of the scene by different light sources is calculated.
Transformation–In transformation, the objects are aligned in perspective as seen
from the observer's point of view.
Back face culling–This process computes hidden surfaces resulting from the
observation perspective chosen. Any object having an invisible front surface is
omitted.
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.
Scaling on the screen – The above steps are now calculated for three-dimen-
sional 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.
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 tex-
tures are computed:
– 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.
–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.
– The MIP mapping method stores a large number of enlargement stages for the
texture. The depth information of a primitive is then used to determine which
enlargement stages of the texture will be used in drawing. Normal textures sel-
dom contain more than 256 colors.
The first 15 bits of a 16-bit wide color representation are reserved for the colors
(5/5/5 > R/G/B). Information concerning the transparency of the texture is car-
ried in the alpha channel. The last bit is reserved for this information. Finally, a
distinction is made in MIP mapping between bilinear and trilinear filtering. Bilin-
ear filtering interpolates between two pixels of two textures, trilinear filtering
interpolates between four pixels for each of two textures.