Forums » Help » collisionMap.trace behaving oddly

In the update function of my player.js entity I have the following code:

var res = ig.game.collisionMap.trace( this.pos.x, this.pos.y, this.pos.x+16, this.pos.y+16, 4, 4 );
if ( res.collision.x || res.collision.y )
{
    this.messagebox = "Collision found........\n" +
		      "\n player is @:\n " + this.pos.x + "," + this.pos.y +
		      "\n collision:\n " + res.pos.x + "," + res.pos.y;
}

Here's an example output of messagebox:

Collision found........
player is @:
224,192
collision:
464,255

It's weird because I'm standing in the middle of an open grassy field in the game. How is it possible that I can be detecting collisions nearby when I'm not near any?

The third and fourth parameters of .trace() should only be 16 - the size of your Entity. Right now the size.x = 224 + 16 and size.y = 192 +16. So essentially, your Entity is freaking huge.

Basically what I'd like to do is this: check if the area directly left (ie. the pixel literally beside the player) is walkable.

Here is my attempt:

var res = ig.game.collisionMap.trace( this.pos.x-1, this.pos.y, 1, 1, this.size.x, this.size.y );

Oddly enough, it only picks up collisions when I'm directly left of a the collision piece.

Oops, my bad. The signature for collisionMap.trace() is this:

trace: function( x, y, vx, vy, objectWidth, objectHeight )

Thus, the 3rd and 4th parameters were not size, but vel.

Previously, your 3rd and 4th parameters were too large, as your entity was moving an immense distance in a single frame. This time, your vel.x = 1, which means your Entity is moving towards the right; so yes, it&039;ll only pick up collisions when your Entity is to the left of the collision tile. If you change it so that #vel.x = -1, your Entity will be moving towards the left, and it'll only pick up collisions when your Entity is to the right of the collision tile.

My god.

vx and vy are velocities...

I was thinking they were a second x and y value such as to create two points to form a rectangle... No wonder I was having a nightmare of a time.

Thanks quid!