如何在Java中平滑地将图形对象移动360度

我正在尝试制作一款《几何战争》风格的游戏，但遇到了障碍。我一直在试图找到一种方法来平滑地移动我的图形对象。但它只朝着一个方向发展。例如，如果我按下向上按钮，它就会向上移动，然后当我按下上面的右按钮时，我会朝着右上角对角移动。但我希望我的物体能顺利地从直上转向右上角。这是我迄今为止的代码：

public class MoveTest extends JPanel implements ActionListener, KeyListener {
Timer t = new Timer(5, this);
double x = 0, y = 0, velX = 0, velY = 0;
 private Set<Integer> pressed = new HashSet<Integer>();
private static int WIDTH = 800;
private static int HEIGHT = 600;
private double d = 0;
private double topSpeed = 0;
private boolean stop = false;
private double a = 0;
PVector location;
PVector velocity;
PVector acceleration;
public MoveTest() {
  location = new PVector(WIDTH/2,HEIGHT/2);
  velocity = new PVector(0,0);
  acceleration = new PVector(0,0);
  topSpeed = 5.0;
  t.start();
  addKeyListener(this);
  setFocusable(true);
  setFocusTraversalKeysEnabled(false);
}
public void paintComponent(Graphics g) {
  super.paintComponent(g);
  Graphics2D g2 = (Graphics2D) g;
  g2.setColor(Color.GREEN);
  g2.drawOval((int)location.x, (int)location.y, 40, 40);
}
void update() {
  velocity.add(acceleration);
  if(stop == false) {
    velocity.limit(topSpeed);
  }
  else {
    velocity.decellerate(0);
  }
  location.add(velocity);    
}
public void north() {
  acceleration = new PVector(0,-5);
}
public void south() {
  acceleration = new PVector(0,5);
}
public void west() {
  acceleration = new PVector(-5,0);
}
public void east() {
  acceleration = new PVector(5,0);
}
public void northEast() {
  acceleration = new PVector(5,-5);
}
public void northWest() {
  acceleration = new PVector(-5,-5);
}
public void southEast() {
  acceleration= new PVector(5,5);
}
public void southWest() {
  acceleration = new PVector(-5,5);
}
public void stop(){
  stop = true;
}

public void actionPerformed(ActionEvent arg0) {
  //System.out.println("" + velocity.x + " " + velocity.y);
  repaint();
  update();
  checkEdges();
}
public void keyPressed(KeyEvent e) {
int code = e.getKeyCode();
stop = false;
pressed.add(code);
if(pressed.size() > 1) {
  if(pressed.contains(KeyEvent.VK_W) && pressed.contains(KeyEvent.VK_D)) {
    northEast();
  }
  if(pressed.contains(KeyEvent.VK_W) && pressed.contains(KeyEvent.VK_A)) {
    northWest();
  }
  if(pressed.contains(KeyEvent.VK_S) && pressed.contains(KeyEvent.VK_D)) {
    southEast();
   }
  if(pressed.contains(KeyEvent.VK_S) && pressed.contains(KeyEvent.VK_A)) {
    southWest();
  } 
}
else if(pressed.size() == 1){
  if(code == KeyEvent.VK_W) {
    north();
  }
  if(code == KeyEvent.VK_S) {
    south();
  }
  if(code == KeyEvent.VK_D) {
    east();
  }
  if(code == KeyEvent.VK_A) {
    west();
  }
}
}
public void keyReleased(KeyEvent e) {
  pressed.remove(e.getKeyCode());
  if(pressed.size() == 0) {
    stop();
  }
}
public void keyTyped(KeyEvent e) {
}
void checkEdges() {
  if(location.x > WIDTH) {
    location.x = 0;
  }
  else if(location.x < 0) {
    location.x  = WIDTH;
  }
  if(location.y > HEIGHT) {
    location.y = 0;
  }
  else if(location.y < 0) {
    location.y = HEIGHT;
  }
}
}

任何帮助都将不胜感激。