[AS2] Vector based bouncing (reflection)

programming flash
1

Hi guys. I am working on a simple game where a ball bounces off the floors and ceilings. It’s movement direction is based on vectors, so it has an angle (in radians) and figures out the X and Y from that. Everything works, except I can’t get it to bounce off the left and right walls correctly. Top and bottom bouncing works fine, but not left and right.

It’s literally one line of code that I can’t get (making an object reflect it’s angle after hitting a wall). I know this has been asked before, but I’ve literally been searching for hours for something that explains this part of it and can’t find anything.

Any help would be great!

onClipEvent (load) {
	speed=15; 
	dir=0.8; //angle in radians
}
onClipEvent (enterFrame) {
//xm and ym are the amount to increment _x and _y
	if (_x+xm>550) { //Right wall
		dir*=-1; //this is wrong...
	}
	if (_x+xm<0) { //left wall
		dir*=-1; //this is wrong...
	}
	if (_y+ym>400) { //floor
		dir*=-1;
	}
	if (_y+ym<0) { //roof
		dir*=-1;
	}
	
//trigonometry to figure x and y movement based on angle (dir)
	xm = speed * Math.cos(dir)
	ym = xm * Math.tan(dir);
	
	_x+=xm;
	_y+=ym;
}
on (keyPress "<Up>") {
	dir+=.3;
}
on (keyPress "<Down>") {
	dir-=.3;
}