Hello,
I have a .obj , but I only want a certain part of the .obj in my scene to render. Is there a way to put a 3D cube over the .obj and write a shader to where the objects only inside the cubed area don’t get rendered, while the cube itself is invisible? Thank you.
Edit: I just re-read your post and realized you are trying to cut away what’s inside the cube not everything outside of it. In that case you can probably just set ZWrite on and Color mask off to only write into the depth buffer.
You have to play with the Render Queue (draw order) to make sure the cube gets drawn before the objects you want masked, and that the background gets drawn before them, but it might work for you and it’s a pretty simple approach. This will have the downside of masking out stuff that is BEHIND the cube, so if you still want that to be visible you’d have to use the discard thing mentioned below.
The rest of this is still valid, and might be useful, but i thought you were asking how to mask what’s inside the cube.
If you want to mask it in screen space, you can use the Stencil Buffer, draw the cube into the stencil buffer and then draw the other objects with the stencil mask set so that they only draw where the stencil buffer is set. That will make a 2d mask, like masking the silhouette of the cube, but it won’t distinguish if the objects are in front of or behind the cube vs inside it (which might be what you want). The main advantage of the stencil buffer is it works with very complicated shapes, like if your cube was a teapot.
If it’s literally only a cube, probably the easiest way to do it is to test the fragment against the cube in the fragment shader and use “discard” to kill fragments outside of the cube.
You might also be able to do some tricks with the depth buffer to accomplish this, but depends on what you’re doing. That can have the added bonus of drawing the “cutout” edge of the mesh.
If the objects are static and don’t need to move, you might want to find a way to do it at build time.