Line intersection with AABB Rectangle?

Question

Preferably without using any kind of loop, as this'll be used in a game.

I wish to intersect a line with a rectangle, of arbitrary size. But I also wish for the intersection point[s] to be returned.

It's possible, I've done a little googling, but still have not worked it out.

The line is defined using (x1,y1,x2,y2). The rectangle has these two points too.

Thanks all, Ruirize

Answer 1

I would recommend simply doing a line-segment-line-segment intersection check on each line segment (edge) that makes up the rectangle. Here is a line segment intersection detection algorithm I wrote ages ago, dredged up from one of my old XNA projects:

// a1 is line1 start, a2 is line1 end, b1 is line2 start, b2 is line2 end
static bool Intersects(Vector2 a1, Vector2 a2, Vector2 b1, Vector2 b2, out Vector2 intersection)
{
    intersection = Vector2.Zero;

    Vector2 b = a2 - a1;
    Vector2 d = b2 - b1;
    float bDotDPerp = b.X * d.Y - b.Y * d.X;

    // if b dot d == 0, it means the lines are parallel so have infinite intersection points
    if (bDotDPerp == 0)
        return false;

    Vector2 c = b1 - a1;
    float t = (c.X * d.Y - c.Y * d.X) / bDotDPerp;
    if (t < 0 || t > 1)
        return false;

    float u = (c.X * b.Y - c.Y * b.X) / bDotDPerp;
    if (u < 0 || u > 1)
        return false;

    intersection = a1 + t * b;

    return true;
}

I will leave inputting each edge into the above method and collecting the results as an exercise to the reader :)