Aiming and directional movement trouble in 2d game

Question

Hi!
Im writing my second game now, and am having the same problems as i had on my first game.
When firing a bullet from a weapon i cant make it go in the exact direction i want it to go. On my last game (http://home.online.no/~stefjako) i made the bullet movements manually sort of. Very dirty. But now i use Math.cos and Math.sin to move it:
public void draw(Graphics2D g2)
          g2.setColor(Color.WHITE);
          g2.drawOval(position.x, position.y, 1, 1);
      * Moves bullet!
     public void move()
          double newX = (double)position.x +Math.cos(angrad)*factor;
          double newY = (double)position.y +Math.sin(angrad)*factor;
          position.setLocation(newX, newY);
          factor += speed;
     } Where angrad is the given angle in radians, factor = 1.0 , and speed = 0.1 by default.
This works kindof... But in certain angles the bullet will move straight in one direction for a while, and then suddenly start going in an angle. (sorry for the awful explaining)!
How do u guys usually make movements work nice and feel smooth?
Thanks!

Answer 1

More or less like you do.
If I should make a example of why you have to use some sort of float value to hold the position, try making a game where the "game objects" move less than a pixel/frame.
If you use a int value for storing the position this will mean that it won't move at all because it will never move a whole pixel.
Look at this
If your object have a int x and int y holding it's current position.
x + 0.8 = x because 0.8 will be rounded to 0
y + 0.7 = y and the same here
That's what happens when you use only int values, float values is almost nessecary to store the position in games.