Erase on collision

kgee

New member
I have a semi-transparent toroid growing over time that represents emissions from a dipole antenna. I want part of the toroid to disappear (be absorbed) when it collides with a radar dish. I am over my head here... I have tried many configurations for both the toroid and the radar dish; collision object in erase mode, static body, rigid body, nothing seems to be interacting. Can someone suggest the best way to approach this problem. I do not have a lot of experience with these features.

thanks!
 

Oldcode

Member
You could try a Gradient texture on the transparency channel and use "Distance to X" or something to control when the torrid goes completely transparent.

Good Luck,
 

pinkmouse

Vacant, pretty vacant
You could try setting the toroid to be lit only by a point light situated at your dipole, (that is set to only illuminate the toroid), then when it passes the dish it will be shadowed and disappear.
 

kgee

New member
This sort of thing?

Yes, that is the general idea. You did that with the point light? My scene is a bit more complex, so my results were not good. The toroid is shaped like a bicycle tire with curvature of the leading edges, plus I have luminosity and transparency settings, so I think that might be interfering with the point lights effectiveness???
 

spherical

New member
While that does work appearancewise in that particular situation, you can still see the portion behind the dish. It's just no longer lit. If there is a background or objects behind the torus, it won't have disappeared. It will still block those distant rays.
 

jeric_synergy

Axes grinder- Dongle #99
While that does work appearancewise in that particular situation, you can still see the portion behind the dish. It's just no longer lit. If there is a background or objects behind the torus, it won't have disappeared. It will still block those distant rays.
I suspect that's just a non-zero ambient.

Possibly some GI, but that seems unlikely.
 

spherical

New member
You're not getting the point. The section after passing the dish needs to actually disappear, not just be non-lit. Making it "go dark" can work in specific situations, like the test shown, but it isn't the solution that the OP asked about. IF the OP's situation is a limbo set, then it can be faked this way. If in any other environment, nada.
 

jeric_synergy

Axes grinder- Dongle #99
Oh right, hmmm..... well, one way would be to use a global-coords clip map. I've used such things to cut off a cable that was supposedly winding around a capstan. You can even reference it to the occluding object so that object an be moved (but usually not rotated).

EG:
clip.jpg
 

pinkmouse

Vacant, pretty vacant
Indeed, it's not perfect, it uses a texture rather than geometry as it was just a quick test. But it produces a result that could be comp-ed in if the OP was in a rush to get things done. I may revisit this if I get the time later today.
 

pinkmouse

Vacant, pretty vacant
This one took a bit longer, but still uses a point light on a plane to generate a (hidden from camera), shadow map, then the raytrace node projects that on the geo. Would be easier in LW12 as you could use the clip input in nodes, (as suggested above! :) ), but I only run 11.3 so had to bodge it a bit.

 

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