Direction vector perpendicular to two points

I have two points in space:

(x,y) (x2,y2)

Using those points I want to draw an object perpendicular to them. How can I find the perpe开发者_开发问答ndicular direction vector with those two points?

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The quickest would probably be:

(- (x2-x), y2-y)

This basically follows from the "Common Rotations" section on about rotation matrices. The negative of this vector is also perpendicular, it's up to you which one you want to use.

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Can't you just flip the X and Y coordinates to find a line perpendicular?