Question

What I’m doing is testing to see what the level of intersection between a circle and rectangle. I would like to find whether the rectangle is completely inside the circle, partially intersecting it, or if there is no intersection at all.

I’ve attached the code that I’ve come up with today, it simply checks the distances from the center of the circle to the corners of the rectangle to determine the level of intersection.

What I’m wondering is there a more efficient way of doing this?

EDIT:
Here is my updated, working code. fullIntersect is my own, I found the partialIntersect snippet on Circle-Rectangle collision detection (intersection). I’m going to leave this open, as I’m still curious as to whether there is a better way of doing this.

    public boolean fullIntersect(float circleX, float circleY, float radius)
    {
        float radsq = radius * radius;
        double xsq = Math.pow(circleX - xPosition, 2);
        double xpwsq = Math.pow(circleX - (xPosition + width), 2);
        double ysq = Math.pow(circleY - yPosition, 2);
        double yphsq = Math.pow(circleY - (yPosition + height), 2);

        if(xsq + ysq > radsq || xsq + yphsq > radsq || xpwsq + yphsq > radsq || xpwsq + ysq > radsq)
            return false;

        return true;

        /* this is what the one if statement does
        double disBotLeft = xsq + ysq;
        double disTopLeft = xsq + yphsq;
        double disTopRight = xpwsq + yphsq;
        double disBotRight = xpwsq + ysq;

        if(disBotRight > radsq) return false;
        if(disBotLeft > radsq) return false;
        if(disTopLeft > radsq) return false;
        if(disTopRight > radsq) return false;

        return true;
        */
    }

    public int intersects(float circleX, float circleY, float radius)
    {
        if(!enabled) return 0;
        double wo2 = width / 2.0d;
        double ho2 = height / 2.0d;

        double circleDistanceX = Math.abs(circleX - xPosition - wo2);
        double circleDistanceY = Math.abs(circleY - yPosition - ho2);

        if (circleDistanceX > (wo2 + radius)) { return 0; }
        if (circleDistanceY > (ho2 + radius)) { return 0; }

        if(fullIntersect(circleX, circleY, radius)) { return 2; }

        if (circleDistanceX <= (wo2)) { return 1; } 
        if (circleDistanceY <= (ho2)) { return 1; }

        double cornerDistance_sq = Math.pow(circleDistanceX - wo2,2) +
                             Math.pow(circleDistanceY - ho2,2);

        return cornerDistance_sq <= (radius*radius) ? 1 : 0;
    }

Answer 1

I think your code does not consider these intersections:

I’ll delete this answer as soon as you enhance your code/question.