mmikk / hextile-demo Goto Github PK

Hi there, and thanks for this repo! Just tried building it in vs2019 and if I run the generated hextile-demo.exe then I get a window but no geometry (and hence no hex tiling) just sky.

Hello! Thanks for sharing your excellent project. I found a small bug in how you correct for the rotation the algorithm applies to the sampling of the normal map.

On this line:

https://github.com/mmikk/hextile-demo/blob/main/hextile-demo/hextiling.h#L89

	d1 = mul(rot1, d1); d2 = mul(rot2, d2); d3 = mul(rot3, d3);

The code applies the same rotation to the derivatives as to the st parameter. This will have the net effect of showing a doubly-rotated normal. What you really want is to apply the inverse rotation. Since the rot matrix is orthogonal, you can simply take the tranpose of the rot matrices like so:

	d1 = mul(transpose(rot1), d1); d2 = mul(transpose(rot2), d2); d3 = mul(transpose(rot3), d3);

This seemed to work for me in my local testing.