angle between two points
snippet in c
angle between two points
user3405
double angle = atan2(y2 - y1, x2 - x1) * 180 / PI;".
processing angle between two points
user3774
PVector v1 = new PVector(10, 20);
PVector v2 = new PVector(60, 80);
float a = PVector.angleBetween(v1, v2);
println(degrees(a)); // Prints "10.304827"