Missing tangents on some vertices

According to that last entry in the thread, the guy suggests setting the r value to 0 if the dividend is 0, but really dividing 1 by 0 would result in infinity, not 0. Considering you're just going to normalize the result anyway, maybe you should try setting it to 1.0 when the dividend of the r value is 0.

I replaced the calculation of r with:

 float div = s1 * t2 - s2 * t1;
 float r = div == 0.0f ? 1.0f : 1.0f / div;;

but there is no change to the calculated tangents. I'll try this with a simple mesh rather than a procedural mesh, so it's easier to debug.