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Distance Field AO graphic errors + strange clipping artefacts

Hi, at the moment I have troubles with Distance Field AO and some strange clipping effects in my scene.

Here is the link to the video where you can see what I mean:


  1. I set the Distance Field resolution scale of the skyscraper to 100. Nevertheless I get this dark stains all over the model.

  2. At the beginning of the video you can see a strange clipping. What is this? How can I avoid this clipping?

  3. There is also a clipping in the shadow. It disappears suddenly.

The scene could look fantastic. But I have no idea how I can solve the clipping and the Distance Field problems.I would be very grateful if you can help me.

Best regards, Andreas

Product Version: UE 4.11 Preview
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asked Mar 29 '16 at 05:12 PM in Rendering

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avatar image Tim Hobson ♦♦ STAFF Mar 30 '16 at 12:32 PM

Hi Andreas,

Can you post images/video for your Distance Field AO view and for the Mesh Distance Fields view. (Show > Visualize > )

I think the overall issue you're going to have with this is that if this is a single large mesh this is not going to work well with Distance Fields. They don't work with large meshes. It's ideal to keep them medium to small sized for the best results.

  1. If you have to set the resolution scale to 100 to start getting better results, this is probably not an ideal mesh for DF. typically for decent quality on even some more complex shapes I've not had to go above a DF Resolution Scale of 10.

  2. The clipping looks like DF Shadows and a poor resolution for the Mesh Distance Field.

  3. CSM (Cascaded Shadow Maps) only work for 200 meters (20000 units) when using a movable light. This is the reason the CSM shadows fade. They are on by default with a movable light. To troubleshoot some DF shadow/AO issues, you can disable the CSM by setting the Dynamic Shadow Distance to 0 in the Details Panel for your Directional Light.


avatar image Maxwell_77 Mar 30 '16 at 01:07 PM

Hi Tim, thank you very much for your answer. I could solve some problems in the meantime. I adjusted the distance of the dynamic shadow. Now the shadow clipping is solved. :-) But the problem with Distance field AO is still there. I unwrapped the whole model. But this didn´t help. It is a pity that DFAO only works with small meshes. Could you improve it in future versions? I have recorded a video where I switched on the DFAO visualizer:


On the one side of the skyscraper the DFAO is not so bad...But on the other side the mesh is completely dark...Very strange...Are there some console commands I could try to enhance the quality of DFAO? Can I switch off the DFAO for definite meshes?

Best regards, Andreas

avatar image Tim Hobson ♦♦ STAFF Mar 30 '16 at 02:17 PM

UV Unwraps won't affect how this is affected.

With large meshes you're going to hit GPU limitations with the system. This is something that as tech is improved can likely be improved as well. The dark shadowing issue is still likely to be the DF Resolution scale. You didn't include an image, but I'm sure the quality is just not there to support better quality with such complex geometry.

You can use the option for Disable Distance Field Lighting for specific meshes in the Details Panel when they are selected, but this will disable them from all distance field effects, such as shadowing as well.

avatar image Maxwell_77 Mar 31 '16 at 06:59 AM

Hi Tim, thank you for your help. I scaled down the model. But this didn´t solve the problem. (I attached 3 pictures) I switched off the DFAO. But this degrades the visual quality greatly. For this reason it is no alternative for me. It is really disappointing that there is no workaround to solve this problem. I expected some console commands which can solve this problem with a powerfull graphics card. I guess a GTX 980 Ti should be able to realize this.

It would be fantastic if you could improve the DFAO in the future. For high-end visualizations this limitations are a big problem.

Best regards, Andreas

alt text alt text alt text

screenshot1.jpg (91.3 kB)
dfao.jpg (60.1 kB)
mesh_df.jpg (43.8 kB)
avatar image Tim Hobson ♦♦ STAFF Mar 31 '16 at 01:16 PM

Would you be willing to share the asset? I could have a look and see if there is a way to get around the artifacts you're having.

One workaround maybe would be if you use a lower scaled version, it's possible that you could potentially use the option for Replace Distance Field Mesh in the Build Settings of the Mesh to put a lower poly version in for shadowing and DFAO. Using smaller scale would probably give better results since DFAO and DFSS do not scale to larger sizes.

avatar image Maxwell_77 Mar 31 '16 at 01:58 PM

Hi Tim, I sent you the link to the model as a private message. :-) In the meantime I could get a better DFAO quality. I scaled the model down more and changed the camera location. At the sunny side the model looks good. But behind it you can see the problems with DFAO. :-(

Best regards, Andreas

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Hi Andreas,

Thank you for the test asset. I've sent you the link to a sample project to help demonstrate the differences you may be seeing with DFAO.

Test Asset Provided:

The main problem I saw with this test asset when I opened the FBX in 3DS Max was that half the models faces were inverted. I correct this and exported that as an additional test asset to test with to show comparison.

Notes for the Test Scene I provided.

  • I disabled the Global Distance Field. This helps since meshes will be grouped. You can see this in the DFAO documentation. This can be disabled by using the CVar r.AOGlobalDistanceField 0

  • Scene is solely lit by the Skylight since we're mostly concerned with troubleshooting DFAO and want to see it from all angles of the building. Directly lit will hit a lot of the AO if not all.

  • In the Skylight use the adjustment for Occlusion Max Distance to be between 1000-1500. You can type in higher values as well, but it's capped at a certain point.

  • In the Skylight adjust the Contrast to be 0.1 (default is 0). This can soften the AO in some of the darker areas on the cleaned up examples.

  • Low Poly Building - This is the low poly I made to be a replacement mesh. I just placed it in here for comparison on its own. DF Resolution Scale 10

  • Cleaned up Building using DF Mesh Replacement. This uses the low poly mesh as it's distance field representation. This helped clear up a lot of issues.

  • This is the original FBX you gave me to use as a test. Evident issues with the inverted faces, not even using two-sided materials will help here. DF Resolution Scale 100

  • Cleaned up mesh with no inverted faces, or at least mostly cleaned up. and provides good results, but the DF resolution scale is 100.

The Other big take-away here is the scale of the mesh scale. I placed the Skeletel Mesh Mannequin that is in the Engine Content folder here for context for size.

The first row has the buildings scaled down to 0.1 in their size and the second row is scaled down to 0.05. You should be able to see the quality difference between the two at this point in terms of how scale will work with DFAO.

Here is a comparison of the three meshes:

alt text

I hope this helps and at least addresses some of the concerns you may have had.


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answered Mar 31 '16 at 06:45 PM

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Tim Hobson ♦♦ STAFF
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avatar image Maxwell_77 Apr 01 '16 at 07:20 AM

Hi Tim, you are the best! :-) Thank you very much for your help and the detailed information. The replacement model you created solves the problem. I never thought that there is a problem in the skyscraper mesh. Your support is awesome.

Best regards, Andreas

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