Object still moving even when the number of move is 0 - actionscript-3

Question

I have an object called player and a virtual joystick controller called joystick and it contains its knob called knob and I've placed the joystick and the knob in a different movieclip.
I use a script to move the player as the amount of movement of the knob.
Here's the code :
function enterFrame(e:Event): void {
if (moving) {
// I move the knob as the touch point moves
// and the player as the knob moves
} else {
// I'm trying to slow down the knob movement to get back to its default position
// and slow down the player movement until it stopped
if (knob.x - joystick.x > 0) {
knob.x -= (knob.x - joystick.x)*.5;
player.x -= -(knob.x - joystick.x)*.9;
}
if (knob.x - joystick.x < 0) {
knob.x += -((knob.x - joystick.x)*.5);
player.x += (knob.x - joystick.x)*.9;
}
if (knob.y - joystick.y > 0) {
knob.y -= (knob.y - joystick.y)*.5;
player.y -= -((knob.y - joystick.y)*.9);
}
if (knob.y - joystick.y < 0) {
knob.y += -((knob.y - joystick.y)*.5);
player.y += (knob.y - joystick.y)*.9;
}
// Then I use trace to trace the player x position
trace(player.x);
}
}
And what I got is when I move the knob to left position and touch_end it, the slow down works but the player keep moving left by .01. But when I move the knob to another directions and touch_end it, the slow down works well until the player stopped.
Why could that happens?
Is there a way I can fix this?

Answer 1

This looks like a floating-point precision effect. If you start with knob.x at 1 and joystick.x at 0.5, you'll get:
knob.x joystick.x knob-joystick knob-joystick/2
1 0.5 0.5 0.25
0.75 0.5 0.25 0.125
0.625 0.5 0.125 0.0625
0.5625 0.5 0.0625 0.03125
0.53125 0.5 0.03125 0.015625
0.515625 0.5 0.015625 0.0078125
It's clearly trending towards zero, but there's a small remaining positive value when you calculate knob.x-joystick.x.
Note: Since your if statement that changes knob.x is in an EnterFrame listener, any joystick changes in response to user input will take longer than this to occur.
Instead of checking that your difference is > 0, check that it's greater than some small guard value, e.g.
if (knob.x - joystick.x > 0.01) {
knob.x -= (knob.x - joystick.x)*.5;
player.x -= -(knob.x - joystick.x)*.9;
}
//etc.
You might also add some guard code at the end of your listener:
if (knob.x > 0 && knob.x < 0.01) {
knob.x = 0;
}
//etc.

Answer 2

Well, after working around it, finally I did it!
I use Math.floor "trick" to force the -0.0249999999999828 (the last position when moving to left which make the player keep moving left even when I'm not control it anymore) to be change to 0.
Here's the code :
function enterFrame(e:Event): void {
.... // bla bla bla
} else {
if (knob.x > joystick.x) {
knob.x -= (knob.x - joystick.x)*.5;
player.x -= -((knob.x - joystick.x)*.9);
}
if (knob.x < joystick.x) {
knob.x += -(Math.floor((knob.x - joystick.x)*.5));
player.x += Math.floor((knob.x - joystick.x)*.9);
}
if (knob.y > joystick.y) {
knob.y -= (knob.y - joystick.y)*.5;
player.y -= -((knob.y - joystick.y)*.9);
}
if (knob.y < joystick.y) {
knob.y += -(Math.floor((knob.y - joystick.y)*.5));
player.y += Math.floor((knob.y - joystick.y)*.9);
}
}
}
I changed the if (knob.x - joystick.x > 0) (and all of kind of this) to if (knob.x > joystick.x) I think it's more efficient to detect where the knob is (right, left, up, down).
Or maybe you guys can find another way more efficient and more exact? It would help me