ELSA Synergy 2000, Руководство пользователя

Страница: 26 / 50

Graphics know-how
|
| ELSA Synergy 2000 |
26
EN
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 inter-
polated. 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.
쑗
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. Information concerning the transparency of the tex-
ture is carried in the alpha channel. Finally, a distinction is made in
MIP mapping between bilinear and trilinear filtering. Bilinear filter-
ing interpolates between two pixels of two textures, trilinear filtering
interpolates between four pixels for each of two textures.
쑗
Bump mapping introduces a new dimension. Relief or raised textures
can only be generated with the other methods in two dimensions
using light and shadow effects.
The staircase effect is corrected by anti-aliasing. This is either done by
interpolating mixed pixels, in which a new color value is computed from
two adjacent color values.
쎲
The frame buffer
The finished image will not be written to the frame buffer until this com-
plex sequence of steps is completed. The frame buffer is made up of
front and back buffer. The back buffer acts as a buffer page, in which the
next image to be displayed is built up. The front buffer is the memory