laser effect with (or without) shaders

Question

Hi

I worked already on laser effects. And I found one that was pretty neat when I added glow effect. But now I need to reproduce a laser a bit similar to that:
Or even simply this first:

I'm now a little bit familiar with shaders and I kind of comprehend its logic. But still, when I try to use immediat geometry (from the navmesh demo), shaders seem to not work. What would be the approach to do such effect? The only thing I'm pretty sure already is that the material must be an add blend mode.

Comments

Little update: With a Quad and a shader I could do an effect similar to the 2nd screenshot. However the quad have to always face the camera the same way and always be at the same place relative to the camera. And in that regard, it's not different than drawing a 2d sprite on the HUD. Example (it looks like a simple 2d triangle):

My problem is that I try to create a volumetric object with alpha from solid meshes. I feel like I'm searching in the wrong direction.

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Alright. Further research leads me to polyboarding. Does someone know how to do polyboarding in godot?