CODEWITHSUNDEEP
java2dcollision-detection
Blackvein
Blackvein

Reputation: 558

2D Vertical/Horizontal collision detection

I'm writing a 2D platformer in Java, and I've run into a problem. I have two objects: Both have bounding boxes, and four coordinates to represent the corners of the boxes.

My issue is that I am trying to find a way to simulate collision, but I just can't seem to do it. I've tried searching all over the place, but most sites just demonstrate OpenGL tactics.

Let us represent the bounding box coordinates like so:

TL: Top-left
TR: Top-right
BL: Bottom-left
BR: Bottom-right

Here is how I originally proposed testing collision:

if(TL1 > TL2 && TL1 < TR2) //X-axis
    //Collision happened, TL1 corner is inside of second object
else if(BL1 < TL2 && BL1 > BL2) //Y-axis
    //Collision happened, BL1 corner is inside of second object

This is a very crude way of showing it, but basically I'm checking to see if a corner intersects the other object. The problem is, it doesn't account for both axii. That is to say, an x-collision will occur even if one object is above the other.

If I check for collision on both axii, then there is no way of telling whether it was a horizontal or vertical collision. Or maybe there is and I haven't figured it out.

Can anyone point me in the right direction?

Upvotes: 0

Views: 1558

Answers (1)

BevynQ
BevynQ

Reputation: 8254

this is from java.awt.Rectangle.

you should be able to modify it to suit the coords you have.

/**
 * Determines whether or not this <code>Rectangle</code> and the specified
 * <code>Rectangle</code> intersect. Two rectangles intersect if
 * their intersection is nonempty.
 *
 * @param r the specified <code>Rectangle</code>
 * @return    <code>true</code> if the specified <code>Rectangle</code>
 *            and this <code>Rectangle</code> intersect;
 *            <code>false</code> otherwise.
 */
public boolean intersects(Rectangle r) {
    int tw = this.width;
    int th = this.height;
    int rw = r.width;
    int rh = r.height;
    if (rw <= 0 || rh <= 0 || tw <= 0 || th <= 0) {
        return false;
    }
    int tx = this.x;
    int ty = this.y;
    int rx = r.x;
    int ry = r.y;
    rw += rx;
    rh += ry;
    tw += tx;
    th += ty;
    //      overflow || intersect
    return ((rw < rx || rw > tx) &&
            (rh < ry || rh > ty) &&
            (tw < tx || tw > rx) &&
            (th < ty || th > ry));
}

Upvotes: 1

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