Text on path incorrect tangent angle

[melchiar]

Version

4.3.0

Test Case

https://jsfiddle.net/melchiar/1vdjfLc8/

Information about environment

Tested with Chrome, Firefox

Steps to reproduce

The new text on path functionality seems to be calculating tangent angle incorrectly at certain points on a curve (note the angle of the l, i, and n characters)

[asturur]

I must have broke something quick, because in the PR looked good.
I think is because i lowered the precision on the step... probably some points become the same, and the angle is then 0. That is exactly what looks like here. The angles that look off, look also 0.

[asturur]

There should be a way to calculate the angle on those curves without using 2 near points, i need to find out.

[asturur]

i think here is the answer:
https://gist.github.com/pbeshai/72c446033a98f99ce1e1371c6eee9644

[asturur]

After one our of coding...

[asturur]

Ok was a dumb error, this seems smooth.

[asturur]

The changes are interesting because they remove one full iteration to find the angle, compared to before.
So is more accurate and is also, let's say, double fast.