An ARC From Here to Infinity

Sunday, May 11, 2008 Sunday, May 11, 2008

I’m obsessed with a number. Not just any number, but those amazing new ARCs. Avatar Rendering Cost!

What, you don’t know what that is?

It’s a new feature in the viewer that hatched a few weeks ago. You can access it via this tortuous and finger-straining mouse path: Advanced Menu ->Rendering->Info Displays->Avatar Rendering Cost. Once you’ve ticked that mysterious option you’ll see strange numbers appear above everyone’s head. Yeah, it’s been well described before. First here, then here and a bunch of other spots too.

It’s great sport to check out the ARCs of a crowd to see who’s got the “heaviest” ARC. Or the lowest. A visitor to Electric Pixels the other night was a mere 33, while some of my friends consistently haul around in excess of Five Thousand ARC (you know who you are!) At the Tonight Live taping last weekend someone in the audience was over Ten Thousand – so unbelievably heavy that my LCD screen actually started warping whenever she was in view.

Nevertheless, my interest in ARC lies elsewhere, specifically regarding the bit about particles found in the Official Blog:

16 points added if prim is a particle emitter. Rationale: Particles create even MORE CPU overhead and consume graphics bus bandwidth.

Hmm. Evidently particle effects take up a unit count of 16.

But do they really?

I don’t think so. In fact, I suspect the 16 is merely a guess. Why? Because all particle effects are not created equal. They vary considerably in their behaviour. Here’s what I mean: I can write a particle script that issues a single particle once every 20 minutes. Your poor viewer will no doubt strain and begin smoking under the tremendous effort required to draw that little puff. If you wait the 20 minutes for it to appear.

On the other hand, I can write a particle script that might emit 1000 particles every 0.01 seconds, and keep each of them visible for a full minute. In other words, after 10 seconds of that, your snappy viewer must draw (1000 / 0.01) * 10 = 1,000,000 particles! Yeowch! Actually, your viewer would stop drawing them after you hit the particle limit as set in your preferences, typically 4096 (although I once met a guy who preferred to set his to 4. Yes, 4. I hope they were the Best Four Particles.)

Ahem, back to the analysis we were developing.

So, a particle effect can develop a workload for your shiny PC of something between say, INFINITY and well, NOTHING! But we gotta count particles as something for the ARC statistic. Let’s see. How about SIXTEEN? Yeah, that’s it!

The Official Mandarins had little choice. They had to plug some number, perhaps based on some statistics or empirical experience. And so sixteen it is.

But you and I know that it is really a guess. So when you are in that sandbox and see a newb setting off a phalanx of sim-cracking blockbuster nukes, mentally add a few more ARC points to ‘em.

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