What's a more efficient way to do collisions? - arrays

Question

Here's my dilemma
I have 4 walls around the stage of my game, when a player hits these walls I do not want to make an if statement for each and every one of the walls checking if the player is hitting it, so I have created an array to hold the walls, then check if the player is hitting that. Now, because I am doing this I will not know what the player is actually hitting if he hits something, and I cannot do a check in my array if he's hitting like [0], [1], [2] etc because then I'm back to doing the checks if he's hitting specific walls. The reason I don't want to do that is for the future, when I add more barriers, buildings, and so on.
So my question is, how can I do collision checks, without hard coding checks on specific objects, and giving some sort of value that can be used for the player to respond to, for example if your hitting the top wall and you can figure that out somehow without doing the above, then make it so you can't walk through or something,
if (main.playerPosKeeper_mc.hitTestObject(this[main.StageCollisions]))
{
trace("hit");
}
StageCollisions is an array which contains all of my barriers in it.
When the player hits anything in StageCollisions, I cannot just simply subtract from his y value, or x value, because I do not know which object he hit, but I also do not want to hard code it so that I check if I'm hitting lets say the top barrier, because then why do an array in the first place if I'm just going back to making static if else statements.
^^ Refrencing this topic
AS3 - How to Cycle States of Character Animations (moving & stopped)
This has been stumping me for a little while, so help would be greatly appreciated. It is a hard question to form so I can clarify points if necessary.

Answer 1

So my question is, how can I do collision checks, without hard coding
checks on specific objects, and giving some sort of value that can be
used for the player to respond to, for example if your hitting the top
wall and you can figure that out somehow without doing the above, then
make it so you can't walk through or something
Right, so you want a way to perform a generic collision response. This can be a big topic. The simplest approach is usually to check for a collision after a move, then reverse the move if there's a collision.
Something like this:
function movePlayer(movementX:Number, movementY:Number):void {
var originalX:Number = player.x;
var originalY:Number = player.y;
player.x += movementX;
if (checkCollision()) {
player.x = originalX;
}
player.y += movementY;
if (checkCollision()) {
player.y = originalY;
}
}
function checkCollision():Boolean {
for each (var wall:MovieClip in walls) {
if (player.hitTestObject(wall)) {
return true;
}
}
return false;
}
This way you could have checkCollision() check 4 walls or 50 walls, it doesn't matter. It won't let the player move into them.
This is just a starting point and there are many ways it can break down or be refined.

Answer 2

Some trivial pseudo code for you to study:
private function collisionCheck(h:Sprite):Sprite{ // pass the hero Sprite into this function and it will return the wall that it hit
for each (b:Sprite in blockArray){ // if your array of hit-able objects is called "blockArray"
if (h.hitTtestObject(b)){ // check the hero Sprite against all objects in the array
return b;
}
}
return null;
}
Then, elsewhere in your code (maybe in your gameTick function or gameLoop function or wherever you have your game logic repeating on each frame:
private function gameTick():void{
var objectHit:Sprite = collisionCheck(_myHero); // this will run the collision check function, and return the sprite that the hero collides with;
if (objectHit != null){
objectHit.alpha = 0.5;
// this will give you a visible representation that your code is indeed working, or not.
}
}
For those moments when your hero isn't colliding with anything, this function will return null. That's why I first check if objectHit is not null before trying to perform an operation on its alpha value. Of course, you will do something other than change its alpha value in your project, but this is something I often do (with the alpha) to quickly get a visual confirmation that things are detecting what they are supposed to.