How to make image effect shader work on transparent objects

I made an edge detection shader and attached it to a camera with a script, but it's not drawing edges on transparent objects, I know it's not supposed to work by default.

Is there any way to make my image effect work on transparent objects ?

 

It should work, unless youre using depth for edge detection. Transparent objects dont write to depth buffer

 

I'm using depth and normal, one of them should work but it's not the case

 

Transparent objects dont write to normals as well, the same reason they dont write to depth.

 

Transparent objects don't write to the depth texture.

The short version is because Unity only renders objects with an opaque queue (2500 or less) to the depth texture or depth normals texture. Transparent objects thus aren't accounted for in image effects that make use of those textures.

The longer version is the depth and depth normals textures can only hold one set of values per pixel, so only the closest surface will be stored. If you have a semi transparent object rendering to the depth they would prevent objects behind them from having their values stored in the texture. That means if you have an object that's 1% visible, it would have an outline, but nothing "behind" it would.

If you want outlines on transparent objects you'll need to use an alpha tested material, or handle outlines manually.

 

Thanks for the answer !

edit: is it possible to hack transparent objects rendering queue while keeping them transparent ? Like tricking unity into thinking that they are opaque ?

 

Yes, you can just change the queue on the material or shader, though the shader needs a shadowcaster pass as that's what's used to render the depth. Most unlit shaders do not have this pass as the assumption is it does not need to cast shadows or be in the depth texture.

But I suspect this won't give you the results you want even if you do get it working.

 

Could you or anyone explain how to do this in URP?