Asus AGP-V5200, Руководство пользователя

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24 ASUS AGP-V5200
textures to/from system host memory is required. By setting aside a portion of
texture memory on the graphics card for use as a texture cache and tracking when
a texture switch takes place, textures can be reloaded to the cache as needed from
a copy kept in host memory when the texture was first downloaded. If the requested
texture is already present in the cache, then no reload is performed.
Ideally, for the greatest flexibility and most efficient use of available texture
memory, all textures should be cacheable. However, for a software texture cache
manager, there is a small performance overhead to be paid for this tracking and
any delay in reloading a swapped out texture (as a texture could be swapped out at
any time by another OpenGL process). By allowing the user to specify the size of
the texture cache through the use of the registry variable
OpenGL.MaxTextureSize
,
an approximate balance between non-swappable and swappable textures can be
made (and hence performance). Thus an application should load any of the real-
time critical textures first because the texture manager will only place textures in
cache and/or host memory if a space of sufficient size is not available in the non-
swappable area of texture memory.
To guarantee all texture requests no matter how large, any texture whose size in
texels is greater than the cache size will be silently filtered down to fit in the cache
(while preserving aspect ratio). On the ASUS AGP-V5200 board the size of the
texture cache allows extra room for all lower mipmap level textures including
border texels.
Texture Filter Modes
The default texture minification filtering for OpenGL involves mip-map filtering.
This gives good textured rendering quality but at the cost of low performance.
Much higher performance can be obtained by changing the default texture filtering
such that the minification and magnification filtering modes are the SAME. Setting
them to
GL_LINEAR
gives good quality bilinear filtering and improved performance.
Setting both modes to
GL_NEAREST
will give nearest neighbor filtering and the
fastest possible performance.
BGRA Extension
The BGRA extension provides an additional pixel color format for compatibility
with the blue, green, red component ordering of Microsoft Windows DIBs (device
independent bitmaps).