Tutorial: 2D Box Collision

2D Box Collision

Theory

If the corner of one square is inside the other square the collision has occurred. For easier reading write 4 functions which check for possible collision on each side (left, right, top, bottom). Then write another function that compares which sides have a possible collision to figure out if collision has actually occurred.

Example

Write a function that checks collision with a single side. Note: sprite is 30 pixels large and getX and getY return the origin point of the sprite which in this case is the top left corner.

bool Blue::possibleCollisionLeft(Orange* orange)

{

        //get necessary coordinates

        int blueLeftSide = getX();

        int orangeLeftSide =  orange->getX();

        int orangeRightSide =  orange->getX() + 30;

        //return true if collision could occur on left side

        if((blueLeftSide <= orangeRightSide) && (blueLeftSide >= orangeLeftSide))

        {

                return true;

        }

        else

        {

                return false;

        }

}

Write a function like this for all 4 sides.

Then bring them all together in another function to compare which ones return true. And don't forget to check if its even colliding with the object you want. If its not then return true, doing this at the beginning of the function will stop the function comparing all the edge functions for no reason.

bool Blue::orangeCollision(Orange* orange)

{
            if(!orange)
            {
                       return false;
            }

        //compare collision function results, return true if a collision has occured

        if((possibleCollisionRight(orange) == true && possibleCollisionBottom(orange) == true)

        || (possibleCollisionLeft(orange) == true && possibleCollisionBottom(orange) == true)

        || (possibleCollisionLeft(orange) == true && possibleCollisionTop(orange) == true)

        || (possibleCollisionRight(orange) == true && possibleCollisionTop(orange) == true))

        {

                return true;   

        }

        else

        {

                return false;

        }

}