alltogether.ps

For each tick of the clock
    For every object in the game
        Get all the other objects in the same grid square
        For each other object in the same grid square
            If object still wants to hear about square sharers in this tick
                Tell the object there is a potential collision
                If the object's bounding box overlaps the other's
                    Object reacts
                    Object indicates if it wants to hear about more square sharers

boundingboxoverlap.ps

// testing whether object a and b overlap

If a's bottom right x coordinate is less than b's top left x coordinate
    There is no collision
If a's top left x is greater than b's bottom right x
    There is no collision
If a's top left y is greater than b's bottom right y
    There is no collision
If a's bottom right y is less than b's top left y
    There is no collision

boundingboxusage.ps

For each other object B in the same grid square as object A
    If object B's bounding box overlaps object A's
        Add B to the list of colliding objects

grenadeoverlappingdustbinside.ps

If this grenade is colliding with an object
    If grenade bounding box overlapping line defining left side of object
        Run reverseAngle() function, passing "left" for sideHit

    If grenade bounding box overlapping line defining right side of object
        Run reverseAngle() function, passing "right" for sideHit

    If grenade bounding box overlapping line defining bottom side of object
        Run reverseAngle() function, passing "bottom" for sideHit

    If grenade bounding box overlapping line defining top side of object
        Run reverseAngle() function, passing "top" for sideHit

gridupdate.ps

If an object moves
    Remove the object from all grid square containers
    Get the x and y coordinates of the object's top left corner
        Determine which grid square the coordinates fall into
        Add the object to that grid square container
        For each of the eight surrounding grid square containers
            Add the object to the container

lineline.js

lineLineCollision: function(p1, p2, p3, p4) {
    var d = ((p4.y - p3.y) * (p2.x - p1.x)) - ((p4.x - p3.x) * (p2.y - p1.y));
    var n1 = ((p4.x - p3.x) * (p1.y - p3.y)) - ((p4.y - p3.y) * (p1.x - p3.x));
    var n2 = ((p2.x - p1.x) * (p1.y - p3.y)) - ((p2.y - p1.y) * (p1.x - p3.x));

    if ( d == 0.0 )
    {
        if ( n1 == 0.0 && n2 == 0.0 )
        {
            return false;  //COINCIDENT;
        }

        return false;   // PARALLEL;
    }

    var ua = n1 / d;
    var ub = n2 / d;

    return (ua >= 0.0 && ua <= 1.0 && ub >= 0.0 && ub <= 1.0);
},

lineLineCollisionPoint: function(p1, p2, p3, p4) {
    var d = ((p4.y - p3.y) * (p2.x - p1.x)) - ((p4.x - p3.x) * (p2.y - p1.y));
    var n1 = ((p4.x - p3.x) * (p1.y - p3.y)) - ((p4.y - p3.y) * (p1.x - p3.x));
    var n2 = ((p2.x - p1.x) * (p1.y - p3.y)) - ((p2.y - p1.y) * (p1.x - p3.x));

    if ( d == 0.0 )
    {
        if ( n1 == 0.0 && n2 == 0.0 )
    		{
            return false;  //COINCIDENT;
        }

        return false;	// PARALLEL;
    }

    var ua = n1 / d;
    var ub = n2 / d;

    x = p1.x + ua * (p2.x - p1.x);
    y = p1.y + ua * (p2.y - p1.y);

    return Point2D.create(x, y);
},

nonoverlappinggrid.ps

// Make a structure to hold all the grid squares
For each grid square
    Make a grid square container

// Put all the objects in the right grid square container
For each object in the world
    Get the x and y coordinates of the object's top left corner
        Determine which grid square the coordinates fall into
        Add the object to that grid square container

// Get all the objects that a certain object is colliding with
Get the grid square container the object is in
    Return all the other objects in that grid square container

overlappinggrid.ps

// Make a structure to hold all the grid squares
For each grid square
    Make a grid square container

// Put all the objects in the right grid square container
For each object in the world
    Get the x and y coordinates of the object's top left corner
        Determine which grid square the coordinates fall into
        Add the object to that grid square container
        For each of the eight surrounding grid square containers
            Add the object to the container

// Get all the objects that a certain object is colliding with
Get the grid square container the object is in
    Return all the other objects in that grid square container

pointb.ps

If line C to A is intersecting with the line defining the left side of the object
    Return "left" and the point of intersection between C to A and the left line

If line C to A is intersecting with the line defining the right side of the object
    Return "right" the point of intersection between C to A and the right line

If line C to A is intersecting with the line defining the bottom side of the object
    Return "bottom" and the point of intersection between C to A and the bottom line

If line C to A is intersecting with the line defining the top side of the object
    Return "top" and the point of intersection between C to A and the top line

reverseangle.js

// take moving object and return angle of movement in opposite direction
reverseAngle: function(movingObj, sideHit) {
    var vector = movingObj.getVelocity().normalize();
    var surfaceNormal = this.getSurfaceNormal(sideHit);
    var d = vector.angleBetween(surfaceNormal);
    return this.adjustForSide(d, sideHit);
},

getSurfaceNormal: function(side) {
    if(side == "left")
        return Vector2D.create(-1, 0);
    else if(side == "right")
        return Vector2D.create(1, 0);
    else if(side == "top")
        return Vector2D.create(0, -1);
    else if(side == "bottom")
        return Vector2D.create(0, 1);
},

adjustForSide: function(angleBetween, sideHit) {
    if(sideHit == "left")
        return angleBetween + 90;
    else if(sideHit == "right")
        return angleBetween - 90;
    else if(sideHit == "top")
        return angleBetween + 180;
    else if(sideHit == "bottom")
        return angleBetween;
},