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Enable/disable shadow map re-rendering for movable lights?

I'd like a way to tell a movable light that it should use its shadow map but that it can (for now) stop re-rendering its shadow map.

I have a house environment with many switchable lights (controlled by lightswitches), and so you'd think stationary lights would be preferable to movable lights. However, in a realistic house environment, basically every light violates the max-of-4-overlapping-stationary-lights limitation, because their attenuation radii reach each other through walls:

alt text

So I don't think I can use stationary lights for switchable lights in a residential environment like this.

The problem with movable lights, of course, is that they need to re-render shadow maps on every frame, which gets prohibitive once you have several of them on. Once I switch on 5-10 movable lights with shadow maps, my frame rates become unacceptable.

For most of my lights, I could "lock" the shadow map most of the time, and only have it re-render the shadow map when I know something dynamic is happening nearby (eg a nearby door opening and closing). The rest of the time, the lights could consult their shadow maps but not re-render them.

Is there any concept of locking and unlocking shadow map re-rendering? One of the big benefits of shadow maps historically is that they can (often) be reused from one frame to the next, and I'd love to take advantage of that in UE4.


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asked Aug 31 '14 at 02:19 PM in Rendering

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This is an optimization that the engine should support but we haven't gotten around to it yet. Each movable light should cache its shadowmaps as long as it isn't moving. We could even separate static objects from ones that are moving and re-rendering the moving ones every frame, that way the 'locking' is automatic.

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answered Sep 03 '14 at 02:06 AM

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avatar image rit Apr 25 '17 at 06:49 AM

Is this optimization feature now supported in UE4?

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