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WTF?

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JTippetts

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I am officially mystified...

I coded a handler to allow me to capture sequences of frames from the game loop, in order to catch my wierd bug in action, and managed to catch a shot of it. These two images are from the same sequence, taken from a stationary location. That is, the loop was just sitting there, repeatedly drawing the same view over and over and over; nothing was changing, so each frame rendered should have been identical to the last. Yet flashes of wierd things sometimes crop up:




Out of 60 frames sampled, this second image was the only one with an artifact cropping up; they only appear intermittently, and the majority of frames are fine. I'm stumped; it's repeatedly drawing the same exact data each frame, so where are these coming from? It looks as if it's drawing from some bad vertices, but damned if I know where they're coming from and why they're not being drawn all the time. I only get these wierd thingamabobs on the Linux build; as noted before, the Windows build runs flawlessly. I've tried 4 different driver versions on two different custom kernels, with the exact same problem each time. I've gone over my code again and again, looking for a buffer overrun or anything else that might explain it. I got nuthin'. I'm starting to hate the world and everything in it.

*mumble grumble*
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> I got nuthin'. I'm starting to hate the world and everything in it.


Bit extreme, no?!

As for the error, have you checked that stuff you expect to be null is actually initialised as zero. I got all sorts of odd, intermittent crap appearing when I realised I took this assumption for granted.

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I know you said it was a static shot but could it be tearing on the refresh? On second thought, it doesn't look like it...

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Quote:
Bit extreme, no?!


Okay, well, maybe it is. There is still some stuff left in the universe that's okay. But there is a fairly large portion of the universe that apparently hates me, and it is this piece that seems to be in charge of this particular aspect of my programming. So it is my duty and civic obligation to hate that piece of the universe in return.

Quote:

As for the error, have you checked that stuff you expect to be null is actually initialised as zero. I got all sorts of odd, intermittent crap appearing when I realised I took this assumption for granted.


I'm currently in the process of going over everything again. It's strange, because if I draw the scene normally, ie not using vertex buffers, it works perfectly. But uploading the data as buffers and drawing from the buffers, I get this. So I thought that maybe there was something wrong in the rendering code that just wasn't showing up when drawing from normal arrays, but I can't find anything. It looks as if it's getting bad verts for some of the tiles it's drawing, but it's rarely for the same tile that it happens. I dunno, maybe I'm just missing something stupidly obvious. I did have to fix a little glitch in the rendering system a few days ago, so maybe I introduced something insidious and evil in the process. *sigh*

Quote:

I know you said it was a static shot but could it be tearing on the refresh? On second thought, it doesn't look like it...


No, I don't think it's tearing. The above-posted example is actually a very mild case; in some instances, the glitch will momentarily blot out the entire screen. Also, you can see that it's still drawing the tile, it's just drawing it using some bogus verts located out in the great beyond somewhere.

Gah.

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Could it be a bad mem chip on the card? How the hell you could check that I don't know...maybe put the card in the windows box...Just grasping at straws...

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LRiotto:

Hmmmm.... You may have put your finger on it.
I just rebooted into the Windows dual boot and tested the Windows build again on this machine, and it looks like it is doing the same exact thing there now. It just might be a hardware problem after all. I tested it once before on the Windows boot on this machine and it worked, but in all honesty I didn't run it for very long and may have just 'gotten lucky' with that run. (Or unlucky, as the case may be.) It seems like it might even be a progressive problem, as it seems to be getting worse. Looks like I'll be doing a little hardware switching this afternoon, and possibly an evening run to Fry's Electronics if it turns out the hardware is pooped (which, I suspect, it probably is). I never even suspected a hardware problem, though that may have just been wishful thinking on my part. [grin]

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