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how do I reveal hidden message when spotlight cone goes over it?

I am creating a forensics detective game for college and I want to implement a ultraviolet light feature that can reveal hidden materials and items on the walls when you shine a light at it. I was hoping if there was anyone on here that can help me out with hot to set something like this up.

Thank you

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Product Version: UE 4.20
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asked Nov 03 '18 at 05:54 PM in Using UE4

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2 answers: sort voted first

When the light is on you can start doing a trace into the world from the camera or the flash light. If you hit a collision object that has a hidden mesh you can switch it to visible, pretty simple. (Assuming you have a base actor class for hidden objects, you can trace by that type of object). Materials can also be done in a similar way by creating dynamic material instances and changing a parameter on the material when hit by the trace.

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answered Nov 03 '18 at 06:42 PM

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Steve SybrSyn
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avatar image Major-Lynx Nov 03 '18 at 08:06 PM

Thank you for that answer but my knowledge of unreal engine is limited. Do you know of any visual aids or tutorials to achieve this?

avatar image Steve SybrSyn Nov 03 '18 at 09:26 PM

Well this is really basic fundamental stuff, so any of the blueprint starter tutorials by epic are a good start. You can find their tutorials on their youtube channel here:


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I know it's a late answer and you've probably solved it on your own, but I have a pack on the Unreal MarketPlace that solves this exact thing: https://www.unrealengine.com/marketplace/en-US/slug/spotlight-reveal

In as simple as I can explain it and just as you said it, think of the Spotlight as a cone. I use a cone shaped mask that works just as a cube or sphere shaped mask inside the material for the surface where you'll be revealing the hidden message. I made the material and function to create this cone mask for my pack.

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answered May 16 '19 at 06:38 PM

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