(Actionscript 3.0) Collision detection for draggable objects? - actionscript-3

Question

I am currently working on a new Flash Game that is a sliding puzzle game. However, most of the pieces are not shaped like squares as in a standard sliding puzzle game, which makes the collision detection between the pieces much harder. I decided to try to program the collision detection between the Yellow L and the White L piece, each of which are a 100X100 squares with a 50X50 square cut off of the corner. Is there anyway to give them collision detection so that they cannot overlap each other?
var YellowLClicked: Boolean=false;
addEventListener(Event.ENTER_FRAME,onEnterFrameHandler);
YellowL.addEventListener(MouseEvent.MOUSE_DOWN, dragYellowL);
YellowL.addEventListener(MouseEvent.MOUSE_UP, DoNotdragYellowL);
YellowL.addEventListener(MouseEvent.ROLL_OUT, DoNotdragYellowL);
function dragYellowL(e:MouseEvent): void{
YellowLClicked=true;
}
function DoNotdragYellowL(e:MouseEvent): void{
YellowLClicked=false;
}
function onEnterFrameHandler(e:Event): void{
if(YellowLClicked){
YellowL.startDrag();
} else YellowL.stopDrag();
//Can you help with this code here?
if(YellowL.hitTestObject(WhiteL)) trace("true"); else trace(false);
}

Answer 1

This is the collision check I use in my tetris-style game. It is in my Main.as file.
private function checkCollision(f:GameField):Boolean{
var p:Piece = f.activePiece;
var a:Array = f.blockArray;
for (var j:int = 0; j < p.numChildren; j++){
var b:Block = p.getChildAt(j) as Block;
// check walls, your will probably have four instead of 3
if (b.hitTestObject(f.leftWall) || b.hitTestObject(f.rightWall) || b.row + b.rowLocal >= f._rows){
return true;
}
}
// check all the blocks in f.blockArray
for (var i:int = 0; i < a.length; i++){
// check the moving PIECE against all other BLOCKS
if (p.hitTestObject(a[i])){
// check every child of the PIECE (these will be the blocks)
for (var j:int = 0; j < p.numChildren; j++){
// excluding the BLOCKS in the moving PIECE
if (p.getChildAt(j).parent != a[i].parent){
var b:Block = p.getChildAt(j) as Block;
// finally, BLOCK vs BLOCK collision check
if (b.hitTestObject(a[i])){
return true;
}
}
}
}
}
return false;
}
This is the constructor for my Piece class:
public function Piece(f:GameField,shape:Array,color:uint)
{
makeGrid();
f.addChild(this);
// the shape array passed to this constructor is shown at the end of my post
_shape = shape;
addBlocks(f,shape,color);
}
private function addBlocks(f:GameField, shape:Array, color:uint):void{
_shape = shape;
for (var i:int = 0; i < shape.length; i++){
var b:Block = new Block(color);
// this uses the Array passed as var "shape" to tell where the block will be in relation to the center of rotation of the Piece instance
b.rowLocal = shape[i].y+2;
b.columnLocal = shape[i].x+2;
// this tells the brick its starting column and row are
b.row = -2;
b.column = 3;
// this is the sum of the local and global coordinates
b.y = (b.rowLocal + b.row) * Main.UNIT_SIZE;
b.x = (b.columnLocal + b.column) * Main.UNIT_SIZE;
// put the block on the display list
addChild(b);
// add the block to the array to use for collision checks in the Main doc
f.blockArray.push(b);
}
}
And the Block class just extends sprite and draws a square (mine has some goodies that don't need to be applied here, so I won't post it).
And finally the calling of the Piece constructor and an example of the shape array that gets passed to it.
var newP:Piece = new Piece(f, arr, color);
and the shape Array:
_shapeArray = [
{shape:new Array(new Point (-2, 0), new Point (-1, 0), new Point (0, 0), new Point (1, 0)),color:_colorArray[0]}, // I
{shape:new Array(new Point (-1, -1), new Point (-1, 0), new Point (0, 0), new Point (0, -1)),color:_colorArray[1]}, // O
{shape:new Array(new Point (-2, -1), new Point (-1, -1), new Point (-1, 0), new Point (0, 0)),color:_colorArray[2]}, // Z
{shape:new Array(new Point (-2, 0), new Point (-1, 0), new Point (-1, -1), new Point (0, -1)),color:_colorArray[3]}, // S
{shape:new Array(new Point (-2, 0), new Point (-1, 0), new Point (0, 0), new Point (-2, -1)),color:_colorArray[4]}, // J
{shape:new Array(new Point (-2, 0), new Point (-1, 0), new Point (0, 0), new Point (0, -1)),color:_colorArray[5]}, // L
{shape:new Array(new Point (-2, 0), new Point (-1, 0), new Point (0, 0), new Point (-1, -1)),color:_colorArray[6]} // T
];
To summarize:
Make a Block class that extends Sprite
Make a Piece class that contains Block instances arranged in a shape that you choose.
Run a collision check between pertinent Block pieces.
edit
This looks like it could work. However, I have one more question: checkCollision() returns a boolean but what I do with that boolean? If the boolean is true, how do I make the objects unable to cross?
This is how I implemented that. Allow the objects to cross each other and then call
if (checkCollision(f)) {
// check collision returned true
// so reverse the last move
// before finishing this game loop
}