Simple constraint

If p₁ follows p₀, then p₁ gets its coordinates from the following set of equations:

Calculate the difference in $x$ and $y$

$d_{p}=p_{0}-p_{1}$

, the length of the hypothenuse

$l_{1}=d_{x}^{2}+d_{y}^{2}$

, difference with given radius, $r$

$p_{d}=d_{x}/l_{1}*r-d_{x}$

, and finally add the difference

$p_{1}+=p_{d}$