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Graphics know-how
25
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ELSA GLADIAC
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EN
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
texture is carried in the alpha channel. Finally, a distinction is made
in MIP mapping between bilinear and trilinear filtering. Bilinear
filtering 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. In bump mapping, the texture is
additionally assigned height information, which allows very realistic
three-dimensional effects to be created.
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, or by using transparent pixels of the same
color which are overlaid over adjacent pixels.
쎲
The frame buffer
The finished image will not be written to the frame buffer until this
complex 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
area where the image that appears on the monitor is located. This
prevents the process of image drawing being visible. The duplicate
storage method is also known as double buffering.
Page flipping: Display on the monitor
The content of the front buffer is displayed on the monitor. When the
drawing process in the back buffer is completed, this image is then passed to
the front buffer in a process known as flipping. Unlike double buffering, the
contents of the back buffer are not transferred to the front buffer and then
output to the display. Instead the display results in alternating between the
front and back buffers.
The next image will only ever be displayed once the image drawing process
in the back buffer is completed. This procedure should be repeated at least
20 times a second to give a smooth representation of 3D scenarios. In this
context, we speak of frames per second (fops), a very important value for 3D
applications. A cinema film runs at 24fps.
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