Instance creation problem

Hi guys
I'm having trouble creating instances of an object, I want a random number to be generated and then based on the number which was choosen create an instance of an object in one of four positions.

The problem I'm having is, my instances are generated fine but there is one that keeps jumping to x 0 and y 0.
Please help!

Code:

---

                        //Enemy Creation
                        if ( Math.random()<0.01 )
                        {
                                var randomX:Number = Math.random()*400;
                                var newEnemy = new Enemy(x,y);
                               
                                if (randomX<101)
                                {
                                        new Enemy(x,y);
                                        army.push(newEnemy);
                                        addChild(newEnemy);
                                        enemy.x=50;
                                        enemy.y=-50;
                                }
                                if (randomX>100 && randomX<201)
                                {
                                        new Enemy(x,y);
                                        army.push(newEnemy);
                                        addChild(newEnemy);
                                        enemy.x=150;
                                        enemy.y=-50;
                                }
                               
                                if (randomX>200 && randomX<301)
                                {
                                        new Enemy(x,y);
                                        army.push(newEnemy);
                                        addChild(newEnemy);
                                        enemy.x=250;
                                        enemy.y=-50;
                                }
                                if (randomX>300 && randomX<401)
                                {
                                        new Enemy(x,y);
                                        army.push(newEnemy);
                                        addChild(newEnemy);
                                        enemy.x=350;
                                        enemy.y=-50;
                                }
                        }

---

All those lines which are just "new Enemy(x,y)" aren't doing anything for you. They construct a new Enemy, and then since you never assign any variable to that Enemy instance, it is immediately lost.

You should type the newEnemy variable as Enemy. But that's not technically a problem here, it's just sloppy not to.

enemy is never defined in the code above. And if it is defined somewhere else, you probably didn't want to use that reference here. You probably wanted to set the x and y of the newEnemy instance.

Your cases overlap. If randomX is set to 100.5, for instance, both the first and second if conditions will be true. I doubt that's what you wanted. You probably want mutually exclusive ranges, and you should use a chain of if-else to shortcut the later cases after one is matched.

Thanks for the reply.
Ok I have realized I have unneeded code which I now removed, I'm new to AS3 but I'm a quick learner :) I have fixed my issue as well. Now I'm working on checking if an enemy instance is already created at the position the new one has to be, basically I don't want them to over lap, I have tried using the:

Code:

---

if ( enemy.hitTestObject( enemy ) )
                {
                        removeChild(enemy);
                }

---

It didn't work, I know this is wrong but at the minute I have no other ideas.
Further help will be much apprecatiated.

My working solution to the Previous problem:

Code:

---

if ( Math.random()<0.05 )
                        {
                                var randomX:Number = Math.random()*400;
                                var newEnemy = new Enemy(-100,-100);
                               
                                if (randomX<100.1)
                                {
                                        army.push(newEnemy);
                                        addChild(newEnemy);
                                        enemy.x=50;
                                        enemy.y=-50;
                                }
                                if (randomX>100 && randomX<200.1)
                                {
                                        army.push(newEnemy);
                                        addChild(newEnemy);
                                        enemy.x=150;
                                        enemy.y=-50;
                                }
                               
                                if (randomX>200 && randomX<300.1)
                                {
                                        army.push(newEnemy);
                                        addChild(newEnemy);
                                        enemy.x=250;
                                        enemy.y=-50;
                                }
                                if (randomX>300 && randomX<400.1)
                                {
                                        army.push(newEnemy);
                                        addChild(newEnemy);
                                        enemy.x=350;
                                        enemy.y=-50;
                                }

---

Please use [code] tags to format your code.

See how you have the lines

Code:

---

army.push(newEnemy);
addChild(newEnemy);

---

in each of your cases? Move those lines outside of all the ifs. Since you're doing it in all cases anyway, you don't need to repeat those lines. That doesn't fix anything, it just makes the code cleaner.

In your hitTestObject line, you are testing enemy against itself. I would hope that it is in the same place as itself, so it would always return true. I don't actually know if it does, but regardless, you don't want to test it against itself. I still don't know what enemy is. I presume it is an instance of Enemy, but I don't know where it's defined. Also, in your ifs, you probably intended to set the coordinates of newEnemy, not enemy.

enemy in an instance of Enemy and it's a block(for now) which moves down. Most of the times enemies get created on top of each other and I'm trying to prevent that. If a position if free then I want to create an enemy there, other wise I don't. I thought I could delete the new created enemy that's touching an already existing one to prevent overlapping.

Okay, but you're not testing whether the new enemy is touching the old enemy (is there only one old enemy? if there are more, why do you have an enemy variable rather than use the army array?)

As it is now, you are doing no checking to see whether there's already an enemy at a position (at least, I don't see how the hittest fits in with with the enemy generation code), and you are moving an OLD enemy rather than positioning the new enemy. The new one will be at 0,0 because you never moved it.

I don't really know what to do, I tried:

Code:

---

                                for each (enemy in army)
                                {
                                        if (hitTestObject(enemy))
                                        {
                                                removeChild(enemy);
                                        }
                                }

---

It didn't work, I'm not sure if this is the right way, maybe there is another way to do this? Perhaps another function which can be helpful?
Thank you for all the help so far.

dammit. I just lost a big post by hitting backspace.

Point one: you need to test newEnemy against enemy. Not putting anything in front of hitTestObject means this.hitTestObject means you are testing the root against enemy.

Code:

---

if (newEnemy.hitTestObject(enemy)){

---

Of course, you can only do that after both are on the display.

Point two: you are not removing enemy from army when you remove it from the display. You'll end up with lots of enemies in army which are no longer on screen which will definitely cause poor performance, and will probably cause errors when you try to do things with them that assume they are on screen (like trying to remove them).

Point three: you are not using a local variable for the iteration, so you are overwriting enemy in that loop. I have strong suspicions that you should not have an enemy variable as you currently do at all.

Point four, relating back to point two: Since you want to alter the array while iterating over it, it's simpler to iterate backwards so that you don't have to adjust your loop while doing work.

Code:

---

for (var i:int = army.length-1; i>=0; i--){
  var nme:Enemy = army[i];
  if (newEnemy.hitTestObject(nme)){
    removeChild(nme);
    army.splice(i, 1); //remove it from the army array too.
  }
}

---

Now the enemies are disappearing very soon after there created, sometimes they get half way through the screen and disappear, so there is no way there touching each other, I'm not sure why this is happening.
I tried an idea I thought of last night: make and object for position 1( x=50 ) and if an enemy touches it a boolean is set to true, if it is untouched set it to false.
Here is what I did unfortunately it doesn't work, again I have no idea why :(

Code:

---

                        //Enemy Creation and Placement
                        if ( Math.random()<0.08 )
                        {
                                var randomX:Number = Math.random()*400;
                                var newEnemy = new Enemy(-100,-100);
                                army.push(newEnemy);
                                addChild(newEnemy);

                                if (randomX<100.1 && place1==false)// Code changes
                                {
                                        enemy.x=50;
                                        enemy.y=-50;
                                }
                               
                                if (randomX>100 && randomX<200.1)
                                {
                                        enemy.x=150;
                                        enemy.y=-50;
                                }
                               
                                if (randomX>200 && randomX<300.1)
                                {
                                        enemy.x=250;
                                        enemy.y=-50;
                                }
                               
                                if (randomX>300 && randomX<400.1)
                                {
                                        enemy.x=350;
                                        enemy.y=-50;
                                }
                               
                                if (pos1.hitTestObject(enemy)) // Code changes
                                {
                                        place1=true;
                                }
                                else
                                {
                                        place1=false;
                                }
                        }

---

P.S. I did this only for position 1 to test it out before doing the rest of the positions.

Bump

Why don't you explain this particular task, and maybe I can write an example that works like you want. I don't think I understand what you're really going for. I'm not sure you do either.

Here's how I understand it now: you have four spawn points. You want to repeatedly (once every so often) spawn an enemy at a random point, but only if that point is unoccupied by any already existing enemy. If the chosen point is occupied, spawn nothing.
Each frame, each enemy moves down the screen some amount. Your spawn points are (50, -50), (150, -50), (250, -50), and (350, -50).
I presume the enemies may be removed after they have left the bottom of the screen.

^^ Yes, this is exactly what I want. An example would be very much appreciated.

I'll see about creating a simple implementation of that when I get home this evening. Shouldn't take too long, but I can't start until after work.

Ok.
I'm glad there are people like you who are so helpful!

Here you go, a simple demo with SpawnPoints, Enemies, and some glue code. I even made the spawn points draggable. :)

Thank you so much!
I will examine and apply the code to my project as soon as I have time( I got a lot of school work :( ).
I will post when I implement the code, Thanks again!

Darn, I have changed the game concept and now I need the enemies to spawn in a random y, there coming from the side and not from spawn points, just random. I done this and it works, but now I only have overlapping code for enemies when there spawned from spawns not with out them. I tried your previous code again and modified it but I still couldn't get it to work, I mean this one:

Code:

---

for (var i:int = army.length-1; i>=0; i--){
  var nme:Enemy = army[i];
  if (newEnemy.hitTestObject(nme)){
    removeChild(nme);
    army.splice(i, 1); //remove it from the army array too.
  }
}

---

Basically the enemies spawn at random y and overlap, I don't want this.
Thanks for all the help so far!

P.S. The problem with the above code is enemies disappear very soon after there created and don't even reach half of the screen.

The problem with that code is that it is removing the enemy that is already on the display instead of preventing a new enemy from going on. You want existing enemies to take priority, so what you need to do is determine if the potential spawn location is free of all enemies. If it is, you can put a new enemy there. If not, don't. But don't remove old enemies until they get across the screen or killed or whatever's appropriate.

I've been searching and while reading some articles I remembered that the code you gave me previously worked but was bad with deleting instances, so I figured I will move them instead and it works when there aren't too much instances of enemy on the screen.
Here is the code:

Code:

---

for (var i:int = army.length-1; i>=0; i--)
                        {       
                                  var nme:Enemy = army[i];
                                  if (newEnemy.hitTestObject(nme))
                                {
                                            nme.y+=100;
                                }
                        }

---

Unfortunately there is a catch,the above code works but I get an error saying:

Code:

---

TypeError: Error #1010: A term is undefined and has no properties.

---

That error indicates that you are referring to some identifier which has not been defined. I see nme declared there, so the remaining possible culprits are army and newEnemy. I'm guessing army is correct since I doubt you'd have changed that much, but how and where is newEnemy declared? Is it available in this scope?

army is declared in the class

Code:

---

public var army:Array;

---

When I try to declare the newEnemy, the code doesn't work, here is what I done:

Code:

---

                        for (var i:int = army.length-1; i>=0; i--)
                        {       
                                var newEnemy=new Enemy(x,y);
                                  var nme:Enemy = army[i];
                                  if (newEnemy.hitTestObject(nme))
                                {
                                            nme.y+=120;
                                }
                        }

---

P.S. I don't know how to declare newEnemy in such a way so it doesn't interfere with other code and i also get a warning:

Code:

---

Warning: 3596: Duplicate variable definition.

---

If you are getting duplicate variable definition, that means that you've already declared that variable in that scope.

You wouldn't want to create a new Enemy each time through the loop anyway, you'd end up creating as many new enemies as you already had enemies, which is going to get big very fast.

Since you're trying to determine whether you want to create a new enemy in the first place, you should not have one until you decide that you want one.

What you should do is iterate through all your existing enemies (which you're doing), but what you should do for each enemy is determine if it hits the proposed point, not another enemy. You could check that it's within some distance of a point too, if you want some margin.
In this case, because you are not altering the army array during the iteration, you do not need to start from the end and go backward. Any old iteration order will do, even the default.

x and y are not great variable names for the proposed spot, since they will shadow the x and y properties of the instance containing this code. I'll change them to px, py for this.

Code:

---

var validSpot:Boolean = true;
for (var i:int = 0; i < army.length; i++){
  var nme:Enemy = army[i];
  if (nme.hitTestPoint(px,py,true)){
    validSpot = false;
    break;
  }
}

if (validSpot){
  //insert code to spawn a new Enemy at px,py.
}

---

Now enemies are created in a straight line one after the other I had to declare px was x and py was y

Code:

---

                        var px:Number=x+500;
                        var py:Number=y;
                        var validSpot:Boolean = true;
                        for (var i:int = 0; i < army.length; i++){
                          var nme:Enemy = army[i];
                          if (nme.hitTestPoint(px,py,true)){
                    validSpot = false;
                    break;
                          }
                        }

                        if (validSpot)
                        {
                                var newEnemy = new Enemy(px,py);
                                army.push(newEnemy);
                                addChild(newEnemy); //insert code to spawn a new Enemy at px,py.
                        }

---

Why are you passing x and y values to the Enemy constructor? If all it's doing is setting its own x and y coordinates, then that's okay but kind of silly. You don't pass alpha, scaleX, scaleY, etc. I'd just set the coordinates after creating.

Anyway, where the enemies get placed will be the point at px, py. It's up to you to select that point appropriately.

Did you mean something like this?

Code:

---

var px:Number =600;
                        var py:Number = Math.random()*400;
                        var validSpot:Boolean = true;
                        for (var i:int = 0; i < army.length; i++){
                          var nme:Enemy = army[i];
                          if (nme.hitTestPoint(px,py,true)){
                    validSpot = false;
                    break;
                          }
                        }

                        if (validSpot)
                        {
                                var newEnemy = new Enemy(x,y);
                                army.push(newEnemy);
                                addChild(newEnemy); //insert code to spawn a new Enemy at px,py.
                                enemy.x=px;
                                enemy.y=py;
                        }

---

It overlaps any way.
I think it would be easier if you seen my game so you could see everything
"Moja Gra" means "My Game"

Can't look at that at work, filters.

hitTestPoint expects the coordinates passed in to be in the Stage coordinate space. If your Enemies are in some container offset from the Stage origin, then it will be testing the wrong point. You can use localToGlobal to get global coordinates from local coordinates.

Ehh this is quite confusin because the solutions look logican but don't work.
Here is my Game class code where everything is controlled:

Code:

---

package
{
        import flash.display.MovieClip;
        import flash.utils.Timer;
        import flash.events.TimerEvent;
        import flash.events.KeyboardEvent;
        import flash.ui.Keyboard;
       
        public class MojaGra extends MovieClip
        {
                //Variables
                public var player:Player;
                public var gametimer:Timer;
                public var Downkey:Boolean;
                public var Upkey:Boolean;
                public var Leftkey:Boolean;
                public var Rightkey:Boolean;
                public var Myspeed;
                public var army:Array;
                public var spawn:Spawn;
                public var speed;
               
                public function MojaGra()
                {
                        //Speed
                        Myspeed=4;
                        speed=3;
                       
                        //Objects
                        player= new Player();
                        addChild(player);
                        player.x = 200;
                        player.y = 200;
                       
                        army = new Array();
                        var randomX:Number = Math.random()*400;
                        var newEnemy = new Enemy( 100, 100);
                        army.push(newEnemy);
                        addChild(newEnemy);

                        //Timer
                        gametimer = new Timer(24);
                        gametimer.addEventListener( TimerEvent.TIMER, Tick);
                        gametimer.start();
                       
                        //Keyboard Listerners
                        stage.addEventListener( KeyboardEvent.KEY_DOWN, onKeyPress);
                        stage.addEventListener( KeyboardEvent.KEY_UP, onKeyRelease);
                }
               
                public function Tick( timerEvent:TimerEvent):void
                {
                        speed+=0.001
                        //Enemy Movement
                        for each (var enemy:Enemy in army)
                        {
                                enemy.Move(speed);
                        }

                        //Enemy Creation and Placement
                        var px:Number =600;
                        var py:Number = Math.random()*400;
                        var validSpot:Boolean = true;
                        for (var i:int = 0; i < army.length; i++){
                          var nme:Enemy = army[i];
                          if (nme.hitTestPoint(px,py,true)){
                    validSpot = false;
                    break;
                          }
                        }

                        if (validSpot)
                        {
                                var newEnemy = new Enemy(x,y);
                                army.push(newEnemy);
                                addChild(newEnemy); //insert code to spawn a new Enemy at px,py.
                                enemy.x=px;
                                enemy.y=py;
                        }

                        //Keyboard Handling
                        if (Downkey==true)
                        {
                                player.y+=Myspeed;
                        }
                       
                        if (Upkey==true)
                        {
                                player.y-=Myspeed;
                        }
                       
                        if (Rightkey==true)
                        {
                                player.x+=Myspeed;
                        }
                       
                        if (Leftkey==true)
                        {
                                player.x-=Myspeed;
                        }
                }
               
                //Keyboard Handling
                public function onKeyPress(keyboardEvent:KeyboardEvent):void
                {
                        if( keyboardEvent.keyCode == Keyboard.DOWN )
                        {
                                Downkey=true;
                        }
                       
                        if( keyboardEvent.keyCode == Keyboard.UP )
                        {
                                Upkey=true;
                        }
                       
                        if( keyboardEvent.keyCode == Keyboard.LEFT )
                        {
                                Leftkey=true;
                        }
                       
                        if( keyboardEvent.keyCode == Keyboard.RIGHT )
                        {
                                Rightkey=true;
                        }
                }
               
                //Keyboard Handling
                public function onKeyRelease(keyboardEvent:KeyboardEvent):void
                {
                        if( keyboardEvent.keyCode == Keyboard.DOWN )
                        {
                                Downkey=false;
                        }
                       
                        if( keyboardEvent.keyCode == Keyboard.UP )
                        {
                                Upkey=false;
                        }
                       
                        if( keyboardEvent.keyCode == Keyboard.LEFT )
                        {
                                Leftkey=false;
                        }
                       
                        if( keyboardEvent.keyCode == Keyboard.RIGHT )
                        {
                                Rightkey=false;
                        }
                }
        }
}

---