I wonder is it possible to implement logarithmic depth in the vertex shader, as opposed to pixel shader? After gl_Position is computed, adjust the vector to apply the logarithm, preserving `xy/w` to keep the 2D screen-space position.
To be clear, I have never tried that and it could be issues with that approach, especially with large triangles. I’m not sure this gonna work, but it might.
I haven't really studied this either so I could be mistaken, but I think it's because OpenGL does the perspective divide between the vertex and fragment shaders, going from clip space to NDC space (which is in the [-1,1] interval and can only be changed by glClipControl()).
The value in gl_FragDepth, if written to, is final, but gl_Position is not and will go through the clip/NDC transformation and since the trick to get the extra precision is to put the depth range into [0,1] instead of [-1,1], this would fail.
So my guess is, it probably wouldn't work on WebGL/OpenGLES without also setting gl_FragDepth, which is, as you mentioned, impractical performance-wise.
