Intel® 945G/945GZ/945GC/ 945P/945PL Express Chipset Family ...

Functional Description
10.5.5.9 Depth Buffer
The raster engine will be able to read and write from this buffer and use the data in per fragment
operations that determine whether resultant color and depth value of the pixel for the fragment are
to be updated or not.
Typical applications for entertainment or visual simulations with exterior scenes require far/near
ratios of 1000 to 10000. At 1000, 98% of the range is spent on the first 2% of the depth. This can
cause hidden surface artifacts in distant objects, especially when using 16-bit depth buffers. A
24-bit Z-buffer provides 16 million Z-values, as opposed to only 64 K with a 16-bit Z buffer.
With lower Z-resolution, two distant overlapping objects may be assigned the same Z-value. As a
result, the rendering hardware may have a problem resolving the order of the objects, and the
object in the back may appear through the object in the front.
By contrast, when W (or eye-relative Z) is used, the buffer bits can be more evenly allocated
between the near and far clip planes in world space. The key benefit is that the ratio of far and
near is no longer an issue, allowing applications to support a maximum range of miles, yet still get
reasonably accurate depth buffering within inches of the eye point.
The GMCH supports a flexible format for the floating-point W buffer, wherein the number of
exponent bits is programmable. This allows the driver to determine variable precision as a
function of the dynamic range of the W (screen-space Z) parameter.
The selection of depth buffer size is relatively independent of the color buffer. A 16-bit Z/W or
24-bit Z/W buffer can be selected with a 16-bit color buffer. Z buffer is not supported in 8-bit
mode.
10.5.5.10 Stencil Buffer
The raster engine will provide 8-bit stencil buffer storage in 32-bit mode and the ability to
perform stencil testing. Stencil testing controls 3D drawing on a per pixel basis, conditionally
eliminating a pixel on the outcome of a comparison between a stencil reference value and the
value in the stencil buffer at the location of the source pixel being processed. They are typically
used in multipass algorithms to achieve special effects (such as, decals, outlining, shadows and
constructive solid geometry rendering).
10.5.5.11 Projective Textures
The GMCH supports two, simultaneous projective textures at full rate processing, and four
textures at half rate. These textures require three floating point texture coordinates to be included
in the Flexible Vertex Format (FVF). Projective textures enable special effects such as projecting
spot light textures obliquely onto walls, etc.
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