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exclude area's from rain particles

Hey all,

I currently have rain set up in my scene, however, it rains everywhere. What would you guys recommend doing to exclude it from certain area's. If we take the example of a shed, I do want it to rain above it, but not undereath it.

Product Version: UE 4.7
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asked May 21 '15 at 12:36 AM in Using UE4

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Vita Cordes
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avatar image theblandyman May 21 '15 at 06:42 AM

Personally, I would create volumes, these anti-effect volumes would turn your rain material's translucency to 0 (or 100, whatever way you see it, point being, it needs to be totally invisible) for the spaces underneath roofing. I believe, however, that if you create a rain particle that has collision, and maybe this particle lives within a 30-40 radius of the player (play with it to see what you need). Past that, you have the old school flat rain approach, where a moving alpha-blended texture simulates distant rain. So you have a physics-based particle system in the player's vicinity (where you can tell the difference, and so close objects have their roofs stop the rain) and a performance-friendly old school effect in the distance. Off the top of my head, that's what I'd do. I think it'd be a good balance, if the transition between the two is smooth.

avatar image Vita Cordes May 21 '15 at 07:43 AM

YES! Finally someone who answeres XD Asked this question in like 5 differend ways and you are first to reply.... and with this many options as well XD

It sounds like that first idea with anti-effect volume is exactly what I need. Problem is tough..... I tried to look into it and came at the precomputed visibility override volume. I added the system to the override invisible actors slot, made sure the brush settings were good. But it doesn't seem to work, I still see my rain inside the box.

What exactly did you have in mind with the anti-effect volumes?

avatar image theblandyman May 21 '15 at 12:05 PM

But i dont think precomputer visibility would have much to do with it. Thats more specialized from what I understand. Im a novice too, beendoing this as a hobby for a looong time but only just dove headfirst

avatar image theblandyman May 21 '15 at 12:04 PM

Thinking about it more, my first idea is dependent on how your rain is set up. The idea would be that if its an animated texture you would make it transparent. But if youre dealing with a live particle system, a better way may be to use those boxes as event collision boxes and when the particle overlaps it, the particle is made translucent or killed. Pm me maybe?

avatar image Vita Cordes May 21 '15 at 12:35 PM

I tried to do it with collision, but collision only works on GPU particles if you are looking at the surface, So if you had a roof above you, it would still go trough it as you are looking at the bottom, which makes the rain go trough. Colission boxes don't work either. And I prefer to stay away from the animated texture screen overlay.

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I would use GPU particle systems and create specific sized volumes of them, setup LODs on them based on the relative size of your volumes and place them in the level.

If your LODs are setup properly with LOD checktimes based on your movement speed and LOD method set to Automatic you should have very little performance issues with a simple translucent rain material using refraction and non-directional or fake lighting...emitting thousands of GPU rain sprites with depthBufferCollision set to kill.

If you use velocity aligned sprites with sizeBySpeed set to high values along Y Axis and low threshold you can get a really nice visual result.

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answered Jun 05 '15 at 01:39 AM

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[Epic]homeRye STAFF
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