Use a depthBuffer for picking

[jailln]

IMO the correct solution is to use a depth buffer (or even stencil buffer) and not a color buffer. Then any issue with lighting is made irrelevant.
Rendering the whole scene will not solve the issue because there may still be objects with the same color as the clear color. It will only make it less likely. (Rendering the whole scene may also reduce performance.)

Originally posted by @Neptilo in #2678

[gchoqueux]

It’s not possible to read the depth buffer directly in WebGL / Three.js, which is why the depth buffer is rendered into a color buffer

[Neptilo]

It's ok if the depth buffer is rendered into a color buffer.
To be clear, in the referenced issue, we're not talking about the general terrain picking but about a glTF object picking which is doing shaded rendering.