Collision not detected

[denisb]

I can't figure out why my spacecraft overlaps with the asteroid and does not collide. I used Phaser.Utils.Debug and found that the display 

objects to not touch each other. Are the bodies in different containers? Thanks for your help.

 

var MyGame={};

MyGame.Level1=function(){
    this.spacecraft;
    this.asteroid;
    this.cursors;
};

MyGame.Level1.prototype={
    
    preload:function(){
        this.load.image('spacecraft', 'assets/spacecraft.png');
        this.load.image('asteroid', 'assets/asteroid.png');
    },
    
    create:function(){
        
        this.game.physics.startSystem(Phaser.Physics.ARCADE);
        this.asteroid=this.add.sprite(500,100,'asteroid');
        this.physics.arcade.enable(this.asteroid,Phaser);
        this.asteroid.body.immovable=true;
        
        this.spacecraft=this.add.sprite(0,100,'spacecraft');
        this.game.physics.arcade.enable(this.spacecraft);

    },
    
    update:function(){
        
        this.physics.arcade.collide(this.spacecraft,this.asteroid,this.collisionHandler,this.processHandler,this);
        
        if(this.game.input.keyboard.isDown(Phaser.Keyboard.UP)){
            this.spacecraft.body.y-=4;
        }
        else if(this.game.input.keyboard.isDown(Phaser.Keyboard.DOWN)){
            this.spacecraft.body.y+=4;
        }    
        if(this.game.input.keyboard.isDown(Phaser.Keyboard.LEFT)){
            this.spacecraft.body.x-=4;
        }
        else if(this.game.input.keyboard.isDown(Phaser.Keyboard.RIGHT)){
            this.spacecraft.body.x+=4;
        }
        
    },

    processHandler:function(spacecraft,asteroid){
        return true;
    },
    
    collisionHandler:function(spacecraft,asteroid){
        spacecraft.kill();
    }
};

[denisb]

It works when I change each axis in update: from this.spacecraft.body.y-=4 to this.spacecraft.body.velocity.y=-200 and so on. Can anyone explain why this works while the other way does not?

 

[koko]

I have a similar problem, does changing collide() to overlap() with the same arguments make it work, cause it does for me? (IDK why however). 

[drhayes]

Physics only works when one of the bodies has a velocity. If they're not moving then the physics system doesn't know how to separate them on collision.

[Cudabear]

drhayes is correct.  In order to correctly use the physics system to detect collisions, you need to give things velocity rather than controlling their positions directly with x and y.  However, if you do use x and y, the overlap() call still works because this just checks for rectangle overlap on the bodies, and doesn't care about velocity.  This can be useful in a few instances, depending on your use case.  As a general statement, however, using physics and velocity is your best bet for consistent game logic.

[koko]

Oh, that makes sense! Thank you. One more question then. If I have a character carrying something and I want to check for a collision with a table, to see if that something was put ON the table, then how am I supposed to move it?

Right now I use a group to 'attach' the object to the hero and I move the whole group which by itself has no body, so I suppose I should rather add the object as a child of hero sprite? Will it inherit parent's velocity so I could detect it's collision with the table or is it basically pointless to check for collision of a child at all?

We're talking about Arcade physics of course.