Derivation of optical depth of view formula H '(apparent depth) = H (actual depth) * n (refractive index) How to push? The best picture, no picture can be said clearly I still don't understand

Derivation of optical depth of view formula H '(apparent depth) = H (actual depth) * n (refractive index) How to push? The best picture, no picture can be said clearly I still don't understand

I can't insert the picture above. If you draw a line perpendicular to the water surface, then draw an oblique one. Make your eyes bigger. Two lights go into your eyes. Oblique from the intersection of the water line and the water line, that is, the depth of view, you can use two right triangles to solve the problem
It's just to draw two light rays at random, and the intersection point that refracts out of the water is the depth of view