MeshTransmissionMaterial turns black mesh gets subtracted

Hi all,

i’m trying to create windows with react-three/csg and the <MeshTransmissionMaterial /> from Drei. I cut out a specific part of the mesh and insert a new Box in it that resembles the window. It worked that way with <meshPhysicalMaterial /> but when using <MeshTransmissionMaterial /> i get a weird black plane behind the glass. Here is a codesandbox showing the issue:

Does anybody know how to fix this issue?

Greetings Tom

  <color attach="background" args={["white"]} />

black is the default clear color in three. you don’t see it because the canvas is transparent by default, but you’ll see it on a webglrendertarget.

That works for the codesandbox, but not for my project unfortunately. Here is a video of the effect in my project:

Do you have any other ideas how to fix it? in my project the background was already set.
I’ll try to recreate it in the codesandbox for better debugging.

im not sure what im seeing tbh. it could be a problem with flipped normals, basically you just want to look through the door i suppose and that should just work. there still has to be a difference between the sandbox and your local project.

I managed to recreate it, and found the solution on the way:

It’s simple, i had the cutouts two times in the same place, creating two glasses above each other. Resulting in this weird looking thing:) Thanks for your time, i wouldnt have asked but i was searching so long for this. It was weird because it worked with MPM so i thought it has to do with MTM.