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Determine if a Point is "behind" a 2D Vector.
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I have a 2D Vector v = (x1,y1) and a Point p = (x2,y2). I want to determine if p is "behind" the vektor.
v allways has the origin 0,0. This illustrates what I mean: http://sketch.odopod.com/sketches/553235
Q would be "behind" the vector while P is "in front" of the vector.
My guts tell me I could us the cross product with z1=z2=0 and check in the result if z3 is negative.
So at the end I should check
x1 * y2 - y1*x2 < 0
<=>
x1*y2 < y1*x2
Which tells me if P is behind v.
But I think that's not absolutely correct. Could you help me?
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