Very simple but large scene creates strange lighting stripes

[jubeco]

I get strange stripes on a cube in a scene with just two objects (one cube, one light) if the light is too far away.

This is a default cube at 0,0,0 with a movable point light at 800,800,800 with an attenuation radius of 2000 and 40 cd.

If you want to re-create this effect follow these steps:

step 1: create a new blank blue script project, no starter content, max quality. You get this:

Step 2: remove all objects in the level:

Step 3: add a simple cube from the Modes tab, at 0,0,0:

Step 4: add a point light from the Modes tab at 800,800,800. Set Intensity to 40 cd, attenuation radius to 2000 and set it as movable:

Step 5: zoom in on the cube

Any help is highly appreciated!

[presto423]

I had something quite similar, with shadow lines on the sides of meshes in the 3rd person shooter template, without changing a thing except maybe setting light to movable. So I checked a ton of settings, and finally got to “Lower Hemisphere is Solid Color”. I disabled it, and the lines disappeared. If it’s not that, it could be in the skylight’s settings somewhere or directional light (light source). What I learned from reading the docs is the Environment is composed of a material, has a resolution (I think default is 32, and don’t know how to change it yet), and bounce lighting (indirect) actually picks up color from it, not only static thru dynamic geometry. So it could be picking up darker areas of the skysphere and reprojecting it to the geometry placed in the level / world. I don’t know if it’s coming through the cubemap, or in the lighting itself separate from the cubemap or how it’s getting thru, but I’m quite sure it is somehow. I had the problem with static / stationary / dynamic lighting, whether mixed or strictly one of those.

[jubeco]

Hi preston42382,

Thanks for your fast response - but I fear it does not address my problem:

• The ‘lower Hemisphere is Solid Color’ is an attribute of the Sky Light which I don’t use. Just to be sure, I tried to add one and set ‘Lower Hemisphere is Solid Color’ to false, but the problem persists.
• I do not have problems with directional lights. This happens only when I use moveable point lights. I went through all its parameter, but was not able to find one that addressed this problem.
• To further simplify the problem - and to avoid any problems with the lightmap and static light propagation - I disabled all static lighting in the project settings, but the problem persists.

[scrcro (scrcr0)]

I believe this is an issue with shadow bias. Try playing with the bias parameter on the light and see if it has any effect.

[jubeco]

Hi scrcr0,

thanks for your idea to play around with the bias. I played around a bit, but according to the ‘conservation law of misery’ I get a new kind of trouble. To demonstrate this I added in the next scene a simple flat cube the Modes Tab and set it to moveable. Then I get this view:

If I decrease the bias the stripes get worse:

If I increase the bias, the stripes go away - but my shadow becomes unusable:

This is the lowest setting where the stripes disappear. The worst part about this setting is, that the part the red arrow is pointing to flickers. So this is not acceptable at all.

As the bias is about self shadowing, I tried to disable the ‘cast shadow’ field of the cube. And all the stripes disappeared (with the original bias of 0.5):

I have implemented some shadow casting algorithms myself and I have not the slightest idea how self shadowing comes into play with a simple cube.

Help!

[jubeco]

I also tried changing the lightmap resolution, this changed nothing - as expected because all objects in this scene are moveable.

[MarcusRivers]

afaik this exact scenario has been a general issue in 3d cgi since as long as i have been using it, in offline renderers you can increase the shadow map resolution, and the option seems to exist in ue, but i see no difference/improvement in increasing the shadow resolution over 2 or 3 in ue

[jubeco]

@MarkusRivers thanks for your kind words. We have now just replaced the point lights by directional lights - which for some reasons don’t have any trouble with the shadow map resolution.

[MarcusRivers]

probably the reason is that point lights will generate 6 seperate shadow maps as its like a 6 way spotlight, and these may overlap and cause banding stripes, or use much lower internal resolution, wheras a directional light only casts in 1 direction and has 1 assoociated map.

[presto423]

I’m getting shadow banding with a directional light, and skylight, no other lights. The bands become narrower and occur in higher frequency when setting CSM number of cascades to 4 instead of 3, and are less frequent / wider at lower than 3 cascades. Turning off CSM gets rid of the bands. It doesn’t matter what lightmap resolution it is, the value of shadow resolution (even at 5), or the other settings of CSM. I also attempted to adjust shadow bias, shadow sharpen filter, tried PCSS via console, and increased MaxCSMResolution to 4096 via console (don’t know if I typed that one correctly), and no change. Perhaps the developers should concentrate on solving these kinds of problems with new versions more than introducing some less important new features. Otherwise the engine becomes too issue-laden to use.

[TorQueMoD]

It’s because your light radius is too high. I recently discovered that increasing the shadow bias will fix the issue. Set it to something like 5 instead of the default 0.5: