I have a line that I draw in a window and I let the user drag it around. So, my line is defined by two points: (x1,y1) and (x2,y2). But now I would like to draw ‘caps’ at the end of my line, that is, short perpendicular lines at each of my end points. The caps should be N pixels in length.
Thus, to draw my ‘cap’ line at end point (x1,y1), I need to find two points that form a perpendicular line and where each of its points are N/2 pixels away from the point (x1,y1).
So how do you calculate a point (x3,y3) given it needs to be at a perpendicular distance N/2 away from the end point (x1,y1) of a known line, i.e. the line defined by (x1,y1) and (x2,y2)?
You need to compute a unit vector that’s perpendicular to the line segment. Avoid computing the slope because that can lead to divide by zero errors.