Dynamic shadows artifacts

[Chosker]

This is more or less universal problem for shadow mapping algorithms.
A bit more details under the spoiler.

I might be wrong but what you describe looks like the standard-issue shadow acne, where the artifacts are caused by screen pixel - shadowmap texel mismatch as you explained.
what we see here, the artifacts that produce faceted-looking shadows being discussed here, really look like a different problem - the problem appears based on the model's topology completely independent from the shadowmap texels



I still think we're missing something here because every other engine out there (including UE3) does not have these faceted-looking shadows we're seeing here and I don't imagine all those other engines out there (old and new) have Receiver plane depth bias implemented (UE3 doesnt for sure).
Regular shadow acne is something we've come to live with and accept, it's a known limitation and it's pretty much in every engine. but this issue here is much more perceivable and it screams bad quality all over the place
if this is indeed the same problem as the regular shadow acne it still feels wrong that it's visible in such a large area of a sphere surface, as in every other engine (including UE3) shadow acne is only really visible at the lights' grazing angles

[Zeblote]

If you look at the screen space projected shadow in renderdoc, before lighting and post processing can hide some of the artifacts, it looks like this:



How can it be so crazy messed up?

[William K]

How can it be so crazy messed up?

Hey it's all crazy man! .

Three reasons, either UE4 has a serious problem with it.

Or UE3 games never used detailed low bias shadows and they where avoiding it that way.

Or both.

[Deathrey]

I might be wrong but what you describe looks like the standard-issue shadow acne, where the artifacts are caused by screen pixel - shadowmap texel mismatch as you explained.
what we see here, the artifacts that produce faceted-looking shadows being discussed here, really look like a different problem - the problem appears based on the model's topology completely independent from the shadowmap texels

It is still same issue. It is just that the larger the shadow filter is, the more grades of shade it will have, to a point where it is hard to see individual acne lines and a face might look uniformly shadowed to a certain degree.

I still think we're missing something here because every other engine out there (including UE3) does not have these faceted-looking shadows we're seeing here

If you take a closer look, the acne on that pic follows the faces of the model exactly the same way, like UE4 problem, that we are discussing. If you bump down UE4 quality settings to a level of UDK defaults, you would see something like this.

and I don't imagine all those other engines out there (old and new) have Receiver plane depth bias implemented (UE3 doesnt for sure).

Nope, indeed. Most had been getting away with a combination of bias and slope-scaled bias.

Regular shadow acne is something we've come to live with and accept, it's a known limitation and it's pretty much in every engine. but this issue here is much more perceivable and it screams bad quality all over the place

The state of the problem in UE4 by default is pretty severe, I'd agree.

if this is indeed the same problem as the regular shadow acne it still feels wrong that it's visible in such a large area of a sphere surface, as in every other engine (including UE3) shadow acne is only really visible at the lights' grazing angles

On a big scale, only few thing have changed since UDK, namely PCF filter size, and shadow resolution. It became larger in UE4 compared to UDK.

Would it be a simple change to copy this over to normal shadows?

Yep.

Hey thanks man for taking the time to explain this, any guesses on the pros and cons as to why Epic may not have chosen the latter two options that would result with relatively better shadowing?

It is hard to guess. Pretty sure they had valid reasons. Simplicity, consistency of results and platform/hardware compatibility comes to mind. Usage of classic slope-scaled depth bias varies slightly between between platforms and imposes restriction on a format of render targets, that can be used for shadow rendering.Implementing it in a hello-world app is incomparably easier, than in established engine. Adaptive bias might not run on every mobile phone out there, plus it has a measurable performance hit and on top of that, it can occasionally produce visual issues far more severe than the issue we are talking about. As opposed to these, flat bias is as simple as a brick and will reliably run on any toaster. Last but not least, up to a certain point, flat bias, backed by soft depth comparison, was just sufficient. In any case, these are just wild guesses as I see it. Whatever was the initial reason, I have a firm faith that UE4 needs slope-scaled bias. It would also be preferable to be able to adjust depth bias and slope-scaled depth bias for each cascade split individually.


Here is a short overview of what one can expect from various biasing techniques in UE4 under the spoiler:

 

Spoiler

depth bias set at 0.5




depth bias set at 4.0




depth bias set at 0.5, with normal offset shadows set at 16




depth bias set at 0.5, unclamped receiver plane depth bias




depth bias set at 0.5, clamped receiver plane depth bias




depth bias set at 0.5, sloped-scaled depth bias set at 16

[Deathrey]

Following previous post, IMGSLI comparison links for convenience:



Bias VS Increased Bias
https://imgsli.com/MTA2MA


Bias VS Bias + SlopeScaledBias
https://imgsli.com/MTA1OQ


Increased Bias VS Bias + SlopeScaledBias
https://imgsli.com/MTA2MQ


Bias VS ReceiverPlaneBias
https://imgsli.com/MTA2Mg


ReceiverPlaneBias VS Bias + ReceiverPlaneBias
https://imgsli.com/MTA2Mw


Bias + ReceiverPlaneBias VS Bias + SlopeScaledBias
https://imgsli.com/MTA2NA


Bias + SlopeScaledBias VS Bias + SclopeScaledBias + ReceiverPlaneBias
https://imgsli.com/MTA2NQ


Bias VS Bias + SclopeScaledBias + ReceiverPlaneBias
https://imgsli.com/MTA2Ng

[Zeblote]

Can you share the code for both methods so we can use whichever works better in game as a temporary solution?

[Deathrey]

Can you share the code for both methods so we can use whichever works better in game as a temporary solution?

I did post RPDB code a few pages behind in the thread. Here are the same files for 4.18.
Cannot share proper slope-scaled depth bias code unfortunately, as there were others involved.

Alternatively you could give a try to this material function for 4.18.1. It mimics slope scaled depth bias, with an exception that unlike the proper one, it operates per-vertex and does not come for free.

[Maximum-Dev]

Working on a moon landscape. Not sure what to do about this.

[DamirH]

Aw ****, I'm a week too late to wish this thread a happy birthday.

[Mark Zubenko]

I encourage everyone to post works, broken due to this issue that you wouldn't be able to showcase otherwise.
Perhaps this will keep the thread afloat and raise the awareness.

[spacegojira]

I encourage everyone to post works, broken due to this issue that you wouldn't be able to showcase otherwise.
Perhaps this will keep the thread afloat and raise the awareness.

That is a great idea, we should do this.

I also encourage everyone to mention this topic everywhere publicly possible, like in other forums, the gamedev reddit or when Epic is publishing a new blog post about how awesome their engine is. This needs a lot more attention.

[Chosker]

That is a great idea, we should do this.

I also encourage everyone to mention this topic everywhere publicly possible, like in other forums, the gamedev reddit or when Epic is publishing a new blog post about how awesome their engine is. This needs a lot more attention.

tried it once, didn't yield any results

https://twitter.com/ChoskerSanz/status/909690139517050880

[spacegojira]

tried it once, didn't yield any results

https://twitter.com/ChoskerSanz/status/909690139517050880

Yes they are trying really hard to ignore us. We just have to keep mentioning it, the more public we get the sooner Epic is coming out of the crypt.

[Maximum-Dev]

Working on a moon landscape. Not sure what to do about this.

[jonimake]

Maybe someone should drive to Epic HQ in Cary, North-Carolina and tell them about this :P