When and how does openGL calculate F_depth(depth value)

[nirla123]

@GClements

The viewport mapping (from zNDC to depth) is affine (i.e. f(x)=a*x+b) with the scale and offset calculated to map [-1,1] to [depthNear,depthFar].

The final depth range transformation is linear? And the formula given in learnopenGL:
F_depth = 1/z-1/near/(1/far - 1/near) is only non-linear because it contains the perspective divide also within the formula?(somehow composed as you had mentioned)

@GClements

• The projection transformation:
  zclip = Czeye+Dweye
  wclip = -zeye
  where C=-(f+n)/(f-n), D=-2fn/(f-n).
• Projective division:
  zNDC = zclip/wclip
• Depth range:
  depth = n + (f-n)*(zNDC+1)/2
  where glDepthRange(n,f) .

I tried to compose the formula as you had mentioned, however I get something different:

Also, alfonse mentioned has mentioned :

View space is not transformed directly into NDC space. View space is transformed into clip-space , where the W component is not necessarily 1. The transformation into NDC space divides the clip-space XYZ by W, then clamps to [-1, 1].

But the viewport transformation is what maps the depth from [-1, 1] to [0,1]. You can’t disregard the very thing you’re talking about.

Is the depth range transformation equivalent to the window viewport transformation?(At least for the z -axis)?