Gradually slow an images movement.

Newbie & Debugging Questions
#1

Right now i have just started a new game and i am controlling basic movement by this code:


		if ((Gdx.input.isKeyPressed(Keys.W)))
			levelY -= 5;
		if ((Gdx.input.isKeyPressed(Keys.A)))
			levelX += 5;
		if ((Gdx.input.isKeyPressed(Keys.S)))
			levelY += 5;
		if ((Gdx.input.isKeyPressed(Keys.D)))
			levelX -= 5;

Now when the keys aren’t pressed the motion stops instantly so I was wondering if there was some formula I could use to gradually slow the movement or maybe not even a formula just another way of doing this. I thought this would be a somewhat discussed subject but my Google searching hasn’t found anything. Thanks in advanced!

#2

By completely controlling the X and Y by inside the if pressed, you wont.

You would need to have a variable like up= true;

I have never done anything like this, so my first thought might not be a very good implementation of this, but here is a example.


if(up){
y -= 5;
slowingDown = 5;
}else if(slowingDown > 0){
y -= slowingDown;
slowingDown--;
}

should slow down till it reaches 0. and the same for left, right and down. you could control it by time differences if you want it to slow down after a certain amount of time instead of after 5 updates.

#3

Wow thank you! That was surprisingly simple. For some reason I thought this would be much more complex…

#4

Uh. That’s kind of bad practice. You should base your game mechanics on physics.

An object in motion stays in motion (Okay. It’s already moving so I should not change an objects velocity.) unless acted upon by an outside force. (Okay. Friction is a force. I will use that.)

There are two types of friction. If you only care about coasting when the arrow key is released, then you only need to worry about kinetic friction. If you’re moving across a solid surface, then friction is proportional to your speed. f = -k * x’ = -k * v = -kinetic_friction_coefficient * speed. Force increases or (in this case) decreases speed in a given direction over time. So you just subtract more or less from the speed depending on the friction, which depends on the speed you are traveling.

if(right && !left)
{
  vx = 5;
} 
else if(left && !right)
{
  vx = -5;
}
else
{
  vx -= 0.5 * vx;
}
x += vx;

If you wanted acceleration when the key is pressed, you would use vx += something instead of vx = something.

Changing k changes how slippery the surface is. A value of zero is frictionless, so you never lose speed. A value of 1 makes you stop instantaneously.

#5

yes, this kind of stuff is all about velocity (how did google not return anything ???)
Just think of a vector pointing in the direction of the image’s movement, and the slow down the speed. Thinking with vectors in libgdx makes things a lot easier.