HP P Class 450/500/550/600/650/700/750 Supplementary Manual page 9

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Occlusion Culling - Why draw what you can't see?
HP is the first to introduce hardware occlusion testing in a personal workstation, and of all the unique features in
VISUALIZE graphics, this is a feature worthy of a close look. Occlusion culling requires specific application
modifications to take advantage of it. The idea is simple: before rendering a portion of a complex image that could
contain thousands of polygons, first see if the object is already hidden by what was rendered before. The cost of the
test involves checking if a bounding volume (think of it as a cube with 6 faces) is already occluded. Because of the
round trip necessary to get the answer back from the hardware, it is more expensive than just rendering the 6 faces.
The actual break-even point for doing the test will vary with the type of data and type of rendering being performed,
but is roughly equivalent to drawing 190 25-pixel triangles on an fx6+, and only 65 25-pixel triangles on an fx2+. As
the processor performance improves, the cost of the test will continue to go down.
Applications written by EAI and Division are already taking advantage of this feature, with dramatic results. More
applications will be released from other companies in the near future. This type of feature will be folded into a
standard interface through the Fahrenheit large model efforts that involve cooperation between HP, Microsoft, and
SGI.
Graphics Benchmarks and Application Performance
Especially with Windows NT, vendors are susceptible to quoting a single benchmark number. When comparing
graphics systems, there is no substitute for benchmarking the actual application you plan to use.
The most popular benchmark used in the last couple of years is the now-obsolete CDRS-03. CDRS is part of the
Viewperf suite of benchmarks sponsored by OPC. The CDRS-03 benchmark had two distinguishing characteristics:
1) it is based on a Display-List application (the application has evolved into PTC Pro/Designer), and 2) it heavily
weights anti-aliased lines. If the applications you plan to use are not display-list based, and you do not frequently
view models using anti-aliased lines, then the CDRS-03 score is irrelevant. All the Viewperf tests (including CDRS)
have a description of the model and the test, and how the test weights various graphics features. To use the Viewperf
data, it is important to know which graphics features are used by your primary OpenGL applications, and then see
which Viewperf test is closest to your application and workloads.
Graphics benchmarks, even those based on the graphics output of real applications like Viewperf, don't simulate the
actual characteristics of running the application on the system. For example, geometry accelerated devices (such as
HP's fx+ series graphics) outperform non-geometry accelerated devices by more than Viewperf results would imply.
The improvement is due to the combination of geometry acceleration and use of DMA to off-load the host CPU,
allowing the application to process data in parallel with the graphics rendering.
03/12/99
Figure 8. Display List Performance
1 2 3
Triangles per Triangle Strip (25 pixel triangles)
4 5 6
fx6+
fx4+
fx4
fx2+
HP 8