Efficient maths algorithm to calculate intersections

Question

For a game I am developing I need an algorithm that can calculate intersections. I have solved the problem, but the way I have done it is really nasty and I am hoping someon

Answer 1

Well, mathematics and scalar products can help there.
- Say you want to intersect segments [AB] and [CD]
- Suppose the line intersection of the lines is M

M is inside segment [ÅB] if and only if
Vector(AB) . Vector(AM) >= 0
and
Vector(AB) . Vector(MB) >= 0

Where the dot "." denotes a scalar product : u . v = ux * vx + uy * vy

So, your algo is :
- find M
- M is inside both segment if and only if the 4 eq below are true
Vector(AB) . Vector(AM) >= 0
Vector(AB) . Vector(MB) >= 0
Vector(CD) . Vector(CM) >= 0
Vector(CD) . Vector(MD) >= 0

Hope this helps