Apply different material on complex object for faces which point backwards (in my case)

[Bossie]

Is it somehow possible to apply specific materials based on the normal of a face?
I have complex 3D objects which can be altered by user-input. So the geometry changes.

Every face should have a default material, and only the faces facing completely backwards should have a different material.

[Bossie]

Shameless self bump

[prisoner849]

Hi!
Any chance to provide a reference pic/vid of the desired result?

[Bossie]

This is the current situation, I use CSG to cut holes in the walls.
I would like to “paint” the inside of the shed a different color.

[Bossie]

More context:

[prisoner849]

Something related:

How to have different colors/textures on bottom and top side of a Plane?

Another option is to use .onBeforeCompile() to modify shaders of built-in materials, using gl_FrontFacing, THREE.DoubleSide and a buffer attribute for the additional set of UV coordinates for back faces of THREE.PlaneBufferGeometry(). [изображение]

Debug winding validator

The simplest option of such material: var mat = new THREE.MeshBasicMaterial({side: THREE.DoubleSide}); mat.onBeforeCompile = shader => { shader.fragmentShader = shader.fragmentShader.replace( `#include <fog_fragment>`, `#include <fog_fragment> gl_FragColor.rgb = gl_FrontFacing ? vec3(0,1,0) : vec3(1, 0, 0); ` ); }