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How to use the Previous Frame Switch node?

It's a new node in 4.15, but I can't find any info on how to use it. Here is a video that shows the effect (less blur caused by Temporal AA, when passing parameters from blueprints): https://www.youtube.com/watch?v=YbjqiNZr4K4

You can also read more about this in the 4.15 release notes: https://www.unrealengine.com/blog/unreal-engine-4-15-released

The node has two inputs. What should I plug into them, and where should I plug the output? Thanks!

Product Version: UE 4.15
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asked Apr 28 '17 at 01:27 PM in Rendering

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avatar image Slavq May 04 '17 at 06:47 PM

Bumpy bump ^^

avatar image iscaru1988 May 11 '17 at 08:45 AM

I'm also interested, I'd like to know how to use this node.

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In the essence, the node allows you separate node networks in material editor, depending on if it is being compiled for present or previous frame.

You would plug that into world position offset, and use your typical WPO animation for Current frame, while adding some compensatory value to the this animation for Previous frame. To get rid of temporal blurring, you might want WPO for previous frame to appear the same, as for Current frame. Thus if you are using something simple for WPO, like sin(Time)*VertexNormal, for previous frame it should be sin(Time+FrameTime)*VertexNormal, where frame time should be supplied as parameter from blueprints/code.

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answered May 11 '17 at 12:30 PM

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avatar image Slavq May 13 '17 at 04:25 PM

Thanks for the clarification. But what if I have a simple animation without Time node, something like that?:

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avatar image Deathrey May 15 '17 at 04:47 PM

Add another scalar value, passed from blueprint. It should match anim phase for previous frame.

avatar image Slavq May 15 '17 at 06:10 PM

Oh, unfortunately I can't add another parameter from collection because I'm hitting the limit (and it must be via parameter collection in my case), but I think I get it how it's supposed to work now. So without additional parameter passed from blueprints it won't fix the blurring - I thought that additional paramater won't be needed. Thanks!

avatar image iscaru1988 May 15 '17 at 06:27 PM

Oh, it's easier to use than what I thought. So if i have a blueprint or c++ class I must create 2 variables, 1 for the current frame time and a second variable for the previous frame time, this way that function in the material calculates the motion vectors correctly. Thanks!!

avatar image MatzeOGH May 16 '17 at 08:55 PM

Is it possible to get some fake motion blur going for a fx? I tried pretty much everything and I haven't noticed any effect

avatar image CupMcCakers Jun 09 '17 at 07:12 PM

second this!

avatar image TUBerlinNUE Nov 14 '17 at 07:55 PM

I still do not know how to use it. What are the inputs? Not just the plain frame times I guess. Could you provide a screenshot, blueprint or C++?

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