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Shadow Mapping Wobble


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#1 AllanRobertson7   Members   -  Reputation: 102

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Posted 20 May 2013 - 10:06 AM

Ive been researching omnidirectional shadow mapping and have been stuck on this problem for a while. Basically the shadows seem to wobble as the camera is moved or rotated. I made a video here:



The problem is most visible about half way through on the gravestones at the bottom of the screen.

The project is implemented in a deferred renderer and at first i thought the problem was to do with aligning texels to pixels but i read that since directx 10 (which i'm using) this is no longer a problem. Someone also suggested that i was updating the camera after the render call so it was a frame behind but this is not the problem.

Any help would be greatly appreciated.

I didn't want to start by posting massive amounts of code. If there is anything needed i can post it.

Edited by AllanRobertson7, 20 May 2013 - 10:08 AM.


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#2 radioteeth   Prime Members   -  Reputation: 1144

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Posted 20 May 2013 - 01:25 PM

looks very much like z-fighting of some sort.



#3 ginkgo   Members   -  Reputation: 294

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Posted 20 May 2013 - 02:14 PM

That looks as if the time at which you render the frame doesn't coincide with the time you render the shadow map.

 

Did you render the shadow map in a previous frame or update the camera settings between sm and frame rendering?



#4 AllanRobertson7   Members   -  Reputation: 102

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Posted 20 May 2013 - 03:32 PM

Thanks for your reply ginkgo, the order things happen in is:

 

camera updates > create geometry buffer > draw shadow maps > draw lights > combine

 

Iv'e just double checked, the camera is definitely only updated once before any rendering code starts.



#5 AllanRobertson7   Members   -  Reputation: 102

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Posted 20 May 2013 - 04:56 PM

I found this post about the same problem for directional lights with an orthographic projection but i cant see if the fix is applicable to perspective point light shadows.

http://www.gamedev.net/topic/591684-xna-40---shimmering-shadow-maps/



#6 MJP   Moderators   -  Reputation: 11774

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Posted 21 May 2013 - 03:14 PM

The temporal aliasing that you get with directional lights occurs because you basically have to move your projection along with the camera, so that it can cover the are that's visible to the camera. Point lights and spot lights are localized, so typically you don't have to change the projection used for rendering the shadows unless the light itself moves. Does your point light stay in the same position in your video, or is it moving?






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