[MAYBE OT] External processor

It would seem most cost-effective to do this with a bunch of cheap networked PC's - you could at least prototype the system this way. Unless you want to make a small self-contained box with a small power supply and without a dozen fans blasting away, there's not much motivation to migrate to embedded processors. If you do, take a look at XScale, particularly if you can convert your algorithms to fixed point or integer arithmetic.

Peter.

Try sci.crypt. I don't know exactly what you're trying to do, but the description of the task sounds like it has the same computational requirements of many massively parallel crypto-cracking boxes.

Yep. Radiosity does that. It's about the most CPU-intensive class of rendering algorithms anybody has dared to actually implement for serious usage, so far.

It can be done, and it has, sort of. Whether you personally can do it is a question of your skills and available funding, of course ;-)

Most large scale animation studios these days are using large farms or clusters of commodity hardware for this kind of work, rather than special-purpose embedded systems.

One or several 19" racks full of 1-HU dual-CPU server modules (or "blades") running Linux seems to be the typical mid-range approach for this kind of problem, these days. Such systems aren't really very strictly embedded ones, but some of the aspects of embedded-dom apply there, too. E.g. the fact that they're typically operated "headless", i.e. without any keyboard and screen attached to them, and that cost and energy usage per unit is more of a limiting factor than on desktops. A fully packed blade server rack can easily burn a couple tens of kilowatts, after all, so you'll want to watch both the electricity bill and your thermal control system closely.

All right, it appears this is not a time-traveling Aprils Fools joke. What in the devil is radiosity?

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will

It's an algorithm from computer graphics. If you've seen any of the recent more-or-less realistically computer-animated movies (Monster, Inc., or Finding Nemo, e.g.), or a high-quality virtual reality model of some building, you'll have seen what it can do.

In a nutshell: it's an application of monte-carlo integration techniques to solve the Rendering Equation.

The Rendering Equation, in turn, is the general physical problem of how to compute what a given scenery (lots of surfaces, of all kinds of materials and colours) will look like in general, by calculating the light being emitted by every patch of surface individually, while taking into account not just light coming to it directly from light sources or mirrors of such, but literally from all over the place.

It's the state of the art for rendering non-shiny surfaces in computer-generated imagery these days. If you read about "Hollywood" switching from SGIs to Linux farms, this is the job they're using all those Linux boxes for.

"Best" is not something we should discuss here --- I've mislaid my asbestos suit ;-)

Fast is also relative --- it doesn't do you any good to have a blazingly fast CPU if you can't afford the power consumption or it melts through the floor for lack of proper cooling.

I don't think you would get very far insisting on no additional chips, at least not without major sacrifices on the raw number-crunching power.

Ethernet is often the method of choice, mainly because it's so readily scaleable, and because it's cheap.

Let's face it: what you're asking about is pretty much a typical number-crunching super computer work-alike, just like all those clusters recently sprouting up at universities all over the world. Typical choices for the processors are ix86 or PowerPC. If you choose one of the x86 variants by VIA or Transmeta that are designed for small systems (large parts of the chipset integrated), you can get away with relatively few additional parts, too. ISTR someone actually did a cluster of PlayStation 2 boxes running Linux, just for the heck of it.

This *will* cost a bunch, though. TANSTAAFL, not even if all you want to eat is CPU cycles.

Thank you. I had heard of the technique, but not the name. I can readily believe the processing needed. Sounds like ray-tracing for lens design exponentiated.

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These guys make their own rendering processors that implement things like dot products as processor instructions. They stuff lots of them into a box and it takes minutes rather than hours.

ISTR the way to cheat radiosity is to calculate it once and then use the results to view the scene from different angles. I guess this assumes that the lights don't move around.

Peter