Get angle between point and origin

This might have been answered before, sorry if it has. I basically need to get the angle from origin to point. So lets say Origin is (0, 0) and my target point is (3, 0).

3 O'clock = 90 degrees

6 O'clock = 180 degrees

9 O'clock = 270 degrees

12 O'clock = 0 degrees

Somehow, I gotta do some math magic, and find out that the angle is 90 degrees (Top is 0). The origin can vary, so I need a method with two parameters, Origin, and TargetPoint, which returns double Angle in Degrees.

Yea, I realize this looks short and nonconstructive, but I made the question as simple and understandable as possible. All the other questions were closed -.-

Thanks

Solution

The vector between two points A and B is B-A = (B.x-A.x, B.y-A.y). The angle between two vectors can be calculated with the dot product or atan2.

var vector2 = Target - Origin;
var vector1 = new Point(0, 1) // 12 o'clock == 0°, assuming that y goes from bottom to top

double angleInRadians = Math.Atan2(vector2.Y, vector2.X) - Math.Atan2(vector1.Y, vector1.X);