Intersecting lines

[xtal256]

I am thinking of making a 2D game in OpenGL and i want to make an easy sort of 'lighting' by setting the vertex colour. I am going to have a number of polygons and when the player is in the polygon, they are coloured whatever colour the 'light' is. But regardless of the reason, i want to know an efficient way to find when 2 lines intersect as is illustrated in the image below.

The player moves into the red 'light' (from a to b) but there are closer vertices that it doesn't go into. So it will have to search all vertices to find the one it wants. Is there a better way?

[K^2]

You might as well check every edge. The line intersection algorithm is extremely easy. All you do is convert each edge into a parametric vector form, and then solve the system of two such equations to find a point of intersections between two lines. All you have to do after is check to make sure that the intersection point is within boundaries of each edge.

 

Would this be easier to understand if I put it in code?

 

Edit: I assume you mean in 2D. Odds of two edges intersecting in 3D are slim. In 3D you'll have to use triangle intersection algorithms which are slightly more advanced.

[xtal256]

I am thinking of making a 2D game in OpenGL

Yes, it is 2D. And no, it wouldn't be too hard to search every point, i only plan to have about 20-30 points anyway.

You can put the code in if you like but i think i will probably just do it when i get around to it.

thanx

[K^2]

I'll let you give it a shot, then, and if you'll have any trouble, let me know.