Opaque shadows on clouds when using megalights + raytraced shadows

Development Rendering
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Hello,

There is a current limitation that when using megalights on a directional light with ray traced shadows enabled, volumetric clouds are unable to receive shadows from opaque geometry, as they cannot sample Virtual Shadow Maps (since they don’t exist for the directional light).

We’d like to be using ray traced shadows for the directional light to avoid the costs of maintaining a VSM, but also keep shadows on clouds. Is there a planned roadmap item to support opaque shadows on volumetric clouds in this configuration? If so, for when is it planned and what can we anticipate that looks like: would be a specialized 2D shadow map or lighting volume like what is used for volumetric fog?

Thanks for your time!

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Hi Eric,

Can you clarify what you mean when you say that you are using ray-traced shadows? Are you talking about the VSM ray-traced shadows feature - shadow map ray tracing (SMRT) or is this something else? As far as I know, we already have directional light support for MegaLights, although I would need to check if we support volumetric clouds for that code path yet.

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Hi again,

You might be missing CL 51377777, which was recently added to the engine to provide shadows for the volumetric cloud component with MegaLights. Are you looking to upgrade to 5.8, or will you be staying on 5.7?

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Hello again, sorry for the late response. I have been out of the office for some time and am only now catching up. I received word that, in fact, we do not support Megalight shadowing on volumetric clouds, as it is not a common enough use case. However, the team has noted your request and will consider it in their future development plans. If you want to add this type of shadow effect to your clouds, we suggest using VSMs. Please let me know if you have any further questions about this.

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Hi,

What I mean is that the directional light is using MegaLights, and its shadowing method is set to “ray traced shadows” instead of “VSM”.

In this configuration, volumetric clouds do not receive shadows from opaque geometry (such as would be the case if there were a large airborne structure above the cloud layer, for example) and I’d like to learn what the plan is to support this case, if any. When the shadowing method is set to VSM, it does receive these shadows.

Thanks

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Hello Tim,

It looks like 51377777 implements the shadow of clouds on other things; the shadowing effect of the cloud is considered during megalights shading and for the megalights lighting volume. However, I’m interested in understanding the plans to support the shadows of other things on clouds, in the configuration I detailed prior.

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This is something that is supported when using Virtual Shadow Maps for the directional light, but not in the configuration I detailed prior. Please do let me know if there is anything planned around this. Thank you!

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