Maths in parallax occlusion mapping shader.

[JasonPhone]

If I'm doing this right, the linear interpolation should be this:

Where the blue dots represent layer depth and red dots are depth sampled from depth map. Then the interpolation is based on the similarity of these two triangles, and the maths goes to:

float weight = abs(afterDepth) / (abs(afterDepth) + abs(beforeDepth)); 

The abs is for negative lengths. But in the fragment shader it is:

LearnOpenGL/src/5.advanced_lighting/5.3.parallax_occlusion_mapping/5.3.parallax_mapping.fs

Line 54 in 3e94252

float weight = afterDepth / (afterDepth - beforeDepth);

And the difference is visible:

Found the same formula here. It uses the sum first and then the subtracted form as a "boiling down". I wonder if this is a simplification or error.