Add block volumetric fog

[Darkinggq]

Describe the project you are working on:
Godot 4 experiment for demo

Describe the problem or limitation you are having in your project:
i only do grid modeling the result looks sad and not good volumetric fog

video -> https://youtu.be/UctZ4BThrqQ

the problem of grid modeling is still visible it is impossible to block the fog and it is not convenient through Add Node -> MeshInstance3D -> PlaneMesh

down without MeshInstance 3D looks awful still visible

only need to block volumetric fog without shadow , UE4 is already there too

Is there a reason why this should be core and not an add-on in the asset library?:
i thought that @reduz seems to have forgotten not added block volumetric fog :)

[SIsilicon]

This is most likely caused by a low, or lack of shadow bias. My Volumetrics plugin has the same problem.
It should be fixable by adding a volume shadow bias control or something; I don't know. I've never used Godot 4.0 before, let alone its volumetric feature. Although my plugin does work similar to what they have from what I can see.

[Calinou]

As a workaround, try making your walls thicker when possible (and make sure they're always solid, with an opaque material on both sides).

[Darkinggq]

As a workaround, try making your walls thicker when possible (and make sure they're always solid, with an opaque material on both sides).

I'm not sure now checking UE4 volumetric fog test result
video -> https://youtu.be/qrAJDvhInZU the walls is all right

volumetric fog the result is not clear I'm experimenting now others demo for godot 4 👍

[reduz]

The one in Unreal is a different type of algorithm (extrusion based), which has different kinds of tradeoffs to the one in Godot. IMO the one in Godot looks more realistic, can read from GI, supports all light types and is more physically correct, but has less resolution (which is also technically more correct because of scattering). I want to add temporal supersampling to it to increase the quality, but you will always have the problem of leaks if you specify too much fog fade in the light settings. You need to reduce this value to eliminate the leaks and ensure walls have some thickness.

In any case, the fog effect is not complete yet, so wait closer to the 4.0 release.

[reduz]

In any case, you will have to wait until there is some documentation written to understand how to use it and work around those use cases.

[reduz]

Let me clarify a bit more so its more obvious. The one you are using in Unreal may look nice but its physically (and geometrically) incorrect. Look at this frame as an example:

The volumetric should follow the path of the light, and here they are incorrect, it should look like this:

[SIsilicon]

I'm not sure now checking UE4 volumetric fog test result
video -> https://youtu.be/qrAJDvhInZU the walls is all right

volumetric fog the result is not clear I'm experimenting now others demo for godot 4 👍

I just watched the video. Is that really volumetric fog? It looks more like a god rays post processing effect.

[reduz]

@SIsilicon it looks like either extrusion based fog, or screen space volumetric fog, neither of which are physically conserving. But it also seems kinda broken so it might be screen space.

[SIsilicon]

@reduz Huh. I never heard of extrusion based fog before; when I look it up, I don't get any meaningful results either. :/

[Darkinggq]

@reduz @Calinou I have already done a demo project took an asset from UE4 the wall size is 0.125m result below screenshot

wall size ok reason volumetric fog visible wall bypasses sad :)

project file download 3.5gb

[Darkinggq]

wall 0.125m not enough we think how big the size of the wall is not comfortable

if this topic closes but users will be in trouble 4.0 alpha/beta will be released soon there will be problems the wall thinks that the problem is volumetric fog

[SIsilicon]

I still think a sort of shadow bias could be implemented to reduce this artifact.
Like push the shadow samples one froxel (frustum voxel) away from, or towards the camera; even have it configurable.

[reduz]

@Madaraz1024 check the fog fade property in the directional light, you can change it to adjust this biasing. The problem is that if you make it too small you will get banding. This is what I need to work on next by implementing temporal reprojection to eliminate it. You can compensate this banding now by changing the shadow filter or by adding fog filtering in the project settings, but it wont be truly solved until I get TR.

[Darkinggq]

one modeling sponza is good volumetric fog the only problem is grid models the ceilings is still bypassed. https://youtu.be/4NBHcEhit34

[reduz]

@Madaraz1024 check my message above on how to adjust bias (fog fade per light). For grid interiors you always need some form of thickness if you use directional lights, else shadowmapping, or even SDFGI will leak light. Its the same with most engines because these techniques are approximate. Only pure raytracing lets you avoid leaks.

[Darkinggq]

two copy meshs copes well with volumetric fog

result great 👍 but not convenient copy meshs wall need thickness not all assets designer modeling the standard always short size accurate, users will submit issues volumetric fog on github alpha 1+ further, etc.

[reduz]

I think most problems in this issue are solved by #45765 so please test again after merged.

[Darkinggq]

@reduz
godot df9c98e, the wall is ok but the problem is the ceiling https://youtu.be/Vw8v_x2EtNo

I added meshinstance the name block_vfog is good but nevertheless the mesh material is visible white needs invisibility example similar MeshInstance > Geometry > Cast Shadow > Shadow Only

can add MeshInstance > Geometry > Cast Shadow > Volumetric Fog Only

I think enough volumetric fog is great :)

[Calinou]

Closing, as the new FogVolume nodes in master allow you to constrain fog to specific areas (by using a positive density value) and exclude fog in specific areas (by using a negative density value). You can use either an additive or subtractive approach, or a mix of both depending on your level design.