Question

I am developing an Android game and I would like to know how to detect the collision of a rectangle knowing its position (x and y), width and height and a triangle knowing x,y, width and height. Triangles are always right triangles as the result of dividing a rectangle through its diagonal so the (x,y) parameter will be a position in the hypotenuse, not the center of the triangle.
Any help would be appreciated!

Answer 1

I´ve finally done this using the function intersect for two lines. Lines are defined with initial point (x,y) and final point (x,y)

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

    Vector2 b = Vector2.Subtract(a2,a1);
    Vector2 d = Vector2.Subtract(b2,b1);
    float bDotDPerp = b.getX() * d.getY() - b.getY() * d.getX();

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

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

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

    intersection = Vector2.Sum(a1,Vector2.Multiply(b,t));

    return true;
}

To know if a triagle intersects a rectangle you check the intersection of every line from the triangle with every line from the rectangle with function above.