Game Development Reference
In-Depth Information
There is a whole range of code optimizations that can be applied to the source code
on the CD. I have deliberately avoided making the code more complex by trying to
wring additional performance from it.
This section is intended to give some general pointers. The advice is based on the
commercial engine I developed and on which cyclone is based. Before you embark
on any optimization effort, I would strongly advise you to get a good profiler (I use
Intel's VTune for PC work) and only optimize areas of the software that you can prove
are causing performance problems.
Caching Contact Data
A relatively simple optimization is to retain the calculations performed during contact
resolution as data in the contact class. When resolving one contact several times, we
currently recalculate its deltaVelocity and other values. These can instead be stored
in the contact data structure and only calculated when first needed.
This is a tradeoff of memory against speed. If you have a large number of contacts
that are only likely to be considered once, then it may be better to leave the algorithm
as is.
Vectorizing Mathematics
The next optimization takes advantage of the mathematical hardware on PCs and
most consoles. This hardware is capable of processing more than one floating-point
number at the same time. Rather than performing all our vector and matrix manip-
ulation as a series of floating-point operations, we can have it process a whole vector
at a time.
For single-precision builds of the engine (things get considerably more complex
for double precision, so we'll ignore that) on a 32-bit PC, we can fit a whole vector
into one of the SSE registers. Using SSE mathematics we can perform a matrix trans-
form of a vector in only four operations. Vector cross products, additions, and other
manipulations are equally accelerated. Most consoles (older hand-helds being the ex-
ception) provide the same facilities. On the Sony PlayStation 2, for example, there is
a dedicated vector mathematics unit you can use for the same effect.
I'm not going to dive into detail about vectorizing mathematics. There is rea-
sonable documentation available with Visual Studio for the Windows PC and many
excellent introductions to the subject online. For serious PC development I would
recommend Intel's Software Optimization Cookbook [Gerber, 2002] (whether or not
you are targeting Intel processors).
Twizzling Rigid-Body Data
The vector mathematics hardware on PCs is optimized to run the same program on
multiple bits of data at the same time. Rather than go through one algorithm per rigid
body, it would be better to run the same algorithm for a group of bodies at the same
time.
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