A. GLperf is an executable benchmark that measures the
performance of OpenGL 2D and 3D graphics operations. These operations
are low-level primitives (points, lines, triangles, pixels, etc.)
rather than entire models such as those used in the Viewperf
Q. What is the purpose of GLperf?
A. The purpose of GLperf is two-fold: to standardize the
method by which vendors report OpenGL primitive performance on their
systems, and to use interactive graphs and other data analysis tools
to present a much fuller performance picture than that provided by
isolated primitive numbers.
Q. Who has developed GLperf and who will maintain it?
A. The benchmark was developed and will be maintained by
the OpenGL Performance Characterization (OPC) project group, a
graphics benchmarking organization that operates under the auspices
of the Graphics Performance Characterization (GPC) Group.
Q. What is a GLperf script?
A. A GLperf script describes the graphics primitives that
will be included in performance tests. One script tests performance,
for example, based on a 50-pixel triangle strip. A script allows many
disparate primitives to be tested during one GLperf run and allows
easy changes and comparisons between different tests.
Q. What GLperf scripts are used for reporting results?
A. The OPC project group has approved a set of 13 GLperf
scripts for reporting results within its Web publication, the GPC
News. These are split into 10 RGB scripts and three color index
scripts. The scripts are further divided by functionality: the
OPClist scripts (RGB and color index) contain a number of tests for a
variety of graphics primitives and other operations (such as
window-clears). These tests are probably the closest parallel to
primitive-level results available from most vendors today. Other
scripts feature specific graphics operations, such as
CopyPixl.rgb, DrawPixl.rgb, ReadPixl.rgb,
TexImage. rgb measure glCopyPixels, glDrawPixels,
glReadPixels and glTexImage2D RGB operations.
DrawPixl.ndx and ReadPixl.ndx are the color index
analogs to DrawPixl.rgb and ReadPixl.rgb .
Remaining scripts address underlying graphics concepts that affect
OpenGL performance -- BgnEnd.rgb measures performance as it
varies with the number of primitives batched together (in a
glBegin/glEnd pair), FillRate.rgb measures how fast
rasterization operations are performed (how many pixels are drawn per
second), Light.rgb measures the effect of the number of
enabled light sources on drawing a particular primitive, and
LineFill.rgb and TriFill.rgb measure the effect of
increasing primitive size on the drawing rates of lines and
Q. Can vendors choose to omit results from some of the
GLperf scripts or tests?
A. No, except for those vendors whose windowing systems or
OpenGL implementations don't support the operations being tested. An
example of this would be a vendor whose windowing system does not
support color index windows, only RGB. This vendor could report all
the RGB results, but omit the color index results.
Q. Why are there so many numbers, instead of just one?
A. One number is certainly preferable for marketing
purposes. It does not serve justice, however, to boil down meaningful
results into one meaningless number. Take the analogy of buying a
car: one must compare many aspects of each car to arrive at the best
buying decision. Most car shoppers do not take totally unrelated
metrics and composite them for comparison purposes. They donít, for
example, take an average of the acceleration, top speed, trunk space,
fuel efficiency, leg room, gas tank capacity and inverted braking
distance. So why would one insist on doing so for something as
complex as 3D graphics performance? Rather, one should choose the
metrics most related to one's needs and compare using those figures.
A CAD user, for example, might not care particularly how fast a
system can transfer an image from memory to the screen, but this is
vitally important to others, such as those in the film and video
Q. What is the difference between Viewperf and GLperf?
A. Both Viewperf and GLperf measure the graphics
performance of a system through the OpenGL API. They were designed,
however, with different goals in mind. While Viewperf draws an entire
model with differing sizes of primitives (as you would see in an
actual application), GLperf artificially assigns a specific size to
every primitive drawn within a test. While Viewperf attempts to
emulate what an application would do graphically and measure it,
GLperf makes no such attempt. Instead, GLperf provides a more
controlled environment within which to extract and measure the
highest performance or "upper bound" of a particular system.
Another difference is that Viewperf reports results in frames
drawn per second, whereas GLperf measures its results in primitives
drawn per second, whether the primitive is pixels, points, lines,
triangles or some other object. To give an analogy to the automotive
world, GLperf would be the equivalent of a speedometer measuring top
speed, while Viewperf would be a stopwatch measuring the average
speed through a slalom course.
Q. How do I look at all these numbers and make sense of
A. A substantial amount of work went into making the
visualization and analysis of GLperf data as simple as possible. This
goal is realized in the form of Java applets that read the GLperf
performance results from the server's database, and allow tabular and
graphical comparisons on the client's web browser. At the top level,
the GLperf visualization tools are broken into two branches: the
OPClist and the other scripts. Going down the OPClist branch, one can
construct a performance comparison by selecting the desired
primitives from one list, and the desired systems on another list.
The other branch allows users to choose from the different GLperf
scripts to display the data that most interests them. Each choice
enables a table to be displayed with graphs on one axis and system
configurations on the other. By selecting different cells, different
sets of data will be displayed. Also, the axes can be linear or a log
scale, allowing the most flexible plotting of data.
Q. What systems are capable of running GLperf?
A. Those systems supporting OpenGL drivers on OS/2, Windows
95, Windows NT and UNIX derivatives.
This document was prepared by John Spitzer, firstname.lastname@example.org, chair of the OPC project group.