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Random numbers are the devil!

Posted by phantom, 05 June 2010 · 134 views

So, as my last post mentioned I had integrated some random number generators into my particle system and the results were very pleasing; once I had the code I could fade particles out with random 'group of four' life times and all was good.

So, I decided to test for speed the other night and hit a slight problem; trying to spawn 1,000,000 particles introduced a 10 second pause in the test app o.O

So, I fired up the beta of Intel's Thread Profiler and set it to work to find out where I was hitting a hotspot. Turned out all this time was being spent in either the forces generator or the ages generator.

As the code was pretty simple, apart from the random number generator, I played a hunch and removed those calls. BAM! Suddenly 1 million particles took pratically no time to spawn.

The solution to this problem; a good old lookup table.
Currently I'm generating two tables of 1,000,000 values each, which is good enough for the testing process at least, but I need a better solution if I plan to use this in other cases.

Chances are 1,000,000 numbers will do me, I just need to think about how to cycle through them when being queried from multiple threads.

Either way, right now 1,000,000 particles takes ~1second to spawn and thrashes the frame rate; I suspect the latter is down to me trying to send 22meg of data PER FRAME across the PCIe bus to the card to render [grin]

I'm going to ponder on a better solution to this problem while also pondering on possible D3DCompute solutions as well. To be honest, really what I want to do this is a new Fusion processor, but those aren't due out for another year [sad] then I probably could throw 1,000,000 around with no problem [grin]

I also need to put proper timing in so I can see how long each segment is taking under different loads, and fix this update problem I have where if you spawn particles after the first trigger it seems they die quicker, but only until all previous particles are dead [oh]

(As I'm now on gardening leave I've got plenty of time to work on this, yay!)




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