(2019-12-14, 14:41)Lasse Deleuran Wrote: However. Since p3 has 0 as the Y-ccordinate, and the cylinder is defined to be between y=10 and y=75, this point is not 'on the cylinder'. My question is how to interpret this position and compute the texture correctly: Should I use p3 in the calculations as if everything is fine, or should I project p3 onto the plane defined by normal (p1p2) and p1 being on the plane?
Neither interpretation gives me the result that you are showing, so I am wondering how you arrived at it.
The spec is a bit vague, but during LDCad's development I discovered it doesn't really matter where p3 is Y-wise.
Just use p3 to calculate a direction vector perpendicular to the p1 p2 vector.
And then use that vector to project the texture to the cylinder's surface by getting the angle between it and similar directional vector pointing at a vertex' position.