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Husbj

Periodic shadow mapping artifacts

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Yet another shadow mapping issue post from me, this is starting to feel like it's on a loop...  :rolleyes:

 

Anyway, I'm experiencing edge shimmering / swimming artifacts for my directional light shadows when "moving" (or rather rotating) the light source. From what I've gathered this is more or less to be expected and not something that is easily dealt with. However, I noticed that the most intrusive artifacts seem to be somewhat periodic rather than random, as you would expect from "roughly the same" view matrix being recalculated for very similar, yet slightly different light directions in succession. I have a video clip showcasing this available here: [media]https:

[/media]

 

Is this a common artifact? And what may be causing it; as said it doesn't look like the random pixel changes you would normally expect from edge shimmering? The green rectangle on the left shows a comparison between the current and last frame's shadow maps (only for the first cascade, but that is what is clearly visible on the columns in the video); for green pixels the stored depth matches within 0.01; if it goes beyond this the pixel at that location is displayed as red instead. As can be seen the red pixels jump around pretty much arbitrarily around the edges of objects for the most part, then there is a significant change where most edges get a full red pixel outline every so often when the light direction changes enough for things to move a pixel in general on the depth map.

Finally (going kind of hand-in hand with the question about what may be causing it), is there any idea on how to alleviate it? I suppose I can live with "normal" edge shimmering if need be but when shadows "jump back" every so often it gets very abrasive in my opinion. I don't think I've seen this particular issue in any games I've played either.

Using variance shadow mapping and applying MSAA to it actually makes the issue less apparent, even though it doesn't cover it up too well. Simple blurring of the shadow map has no effect however.

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I'm going to bump this on the off chance that somebody who haven't already seen it would have any ideas.

Sorry if this isn't allowed.

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