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JDGamedev

Trouble Smoothly Moving Player Sprite

6 posts in this topic

I'm having trouble smoothing out the movement of a player in the game I'm working on. I've just started screwing around with Java2D stuff so it's all very basic fyi.

The problem is that my player stops moving when changing to the opposite direction. Here's an example to explain it further:

When I hold 'D' to move the player right, then push and hold 'A' to change direction, everything works fine. However, when I release 'A' while still holding 'D', my player stops instead of going back to the right. This is clearly because I haven't pressed 'D' again, but I want him to move as long as I'm holding the key, not just when I press it.

I hope that makes sense, and here is the relevant code (hopefully I get it all in here). Any help would be greatly appreciated. Thanks

[u][b]Here is the key even stuff.[/b][/u]
[source lang="java"] // key event stuff
addKeyListener(new KeyAdapter(){
public void keyPressed(KeyEvent ke){
if(ke.getKeyCode() == KeyEvent.VK_W){
p1.playerDirections(Player.MOVE_UP);
}
if(ke.getKeyCode() == KeyEvent.VK_S){
p1.playerDirections(Player.MOVE_DOWN);
}
if(ke.getKeyCode() == KeyEvent.VK_A){
p1.playerDirections(Player.MOVE_LEFT);
}
if(ke.getKeyCode() == KeyEvent.VK_D){
p1.playerDirections(Player.MOVE_RIGHT);
}
}
public void keyReleased(KeyEvent ke){
if(ke.getKeyCode() == KeyEvent.VK_W){
p1.stopY();
}
if(ke.getKeyCode() == KeyEvent.VK_S){
p1.stopY();
}
if(ke.getKeyCode() == KeyEvent.VK_A){
p1.stopX();
}
if(ke.getKeyCode() == KeyEvent.VK_D){
p1.stopX();
}
}
public void keyTyped(KeyEvent ke){

}

});
}[/source]
[u][b]Here is the player class stuff:[/b][/u]

[source lang="java"] public Player(World w){
world = w;
playerImg = new ImageIcon("res/player.png").getImage();
playerRect = new Rectangle(50, 50, playerWidth, playerHeight);
}

private void setXDir(int dir){
xDir = dir;
}
private void setYDir(int dir){
yDir = dir;
}

public void update(){
}

public void draw(Graphics g){
g.drawImage(playerImg, playerRect.x, playerRect.y, playerWidth, playerHeight, null);
}

// setting directions for player movement
public void playerDirections(int nav){
switch(nav){
default: System.out.println("That is not a valid entry for changing maps.");
case MOVE_UP:
setYDir(-1);
break;
case MOVE_DOWN:
setYDir(1);
break;
case MOVE_LEFT:
setXDir(-1);
break;
case MOVE_RIGHT:
setXDir(1);
break;
}
}

// move player based on directions
// methods for controlling movement
public void move(){
playerRect.x += xDir;
playerRect.y += yDir;
}

public void stopX(){
setXDir(0);
}
public void stopY(){
setYDir(0);
}[/source]
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One suggestion I have is to use physics to make the movement instead of moving the sprites statically unless your trying to get that look. Then you can just apply impulses to move your sprite around. You will get much smoother movement, by updating your sprite this way, and it will look more realistic. Check out this [url="http://www.rodedev.com/tutorials/gamephysics/"]link[/url]. Edited by DevLiquidKnight
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It's because the way you are handling moving your player around the screen with the KeyEvent class.....is the simple answer.

You havent mentioned in your post in any way - why you think this unexpected result is happening (as in the player just stops). Read the code back to yourself and then tell us why.

We would need to see your complete code to give more suggestions. You are probably using an AL for example.

Hint: There will be several changes to make to the different class files.
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Your code is being executed when a key is triggered or released. Try checking when a key is pressed (which is what you want, after all).
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You could try separating the movement from the key listener:

[source lang="cpp"]
// key event stuff
addKeyListener(new KeyAdapter(){
public void keyPressed(KeyEvent ke){
if(ke.getKeyCode() == KeyEvent.VK_W){
bMoveUp = true;
}
if(ke.getKeyCode() == KeyEvent.VK_S){
bMoveDown = true;
}
if(ke.getKeyCode() == KeyEvent.VK_A){
bMoveLeft = true;
}
if(ke.getKeyCode() == KeyEvent.VK_D){
bMoveRight = true;
}
}
public void keyReleased(KeyEvent ke){
if(ke.getKeyCode() == KeyEvent.VK_W){
bMoveUp = false;
}
if(ke.getKeyCode() == KeyEvent.VK_S){
bMoveDown = false;
}
if(ke.getKeyCode() == KeyEvent.VK_A){
bMoveLeft = false;
}
if(ke.getKeyCode() == KeyEvent.VK_D){
bMoveRight = false;
}
}
public void keyTyped(KeyEvent ke){

}

});[/source]

[source lang="cpp"]
// check if player is moving and set direction

if (bMoveUp) setYDir(-1);
[color=#000000] else if (bMoveDown) setYDir(1);[/color]
[color=#000000] else setYDir(0);[/color]

[color=#000000][font=Consolas,] if (bMoveLeft) setXDir(-1);[/font][/color]
[color=#000000][font=Consolas,] else if (bMoveRight) setXDir(1);[/font][/color]
[color=#000000] else setXDir(0);[/color]
[/source]
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[quote name='eFoDay' timestamp='1342031043' post='4958119']
You could try separating the movement from the key listener:
[/quote]

Thanks for that. I actually mimicked the movement from a Ludum Dare submission which helped a ton. I pretty much did what you just mentioned. Now if I could just figure out this damn collision detection...
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A small modification's of eFoDay's snippet:

[code]
// check if player is moving and set direction

int dx = 0;
int dy = 0;

if ( bMoveUp ) dy--;
if ( bMoveDown ) dy++;
if ( bMoveLeft ) dx--;
if ( bMoveRight ) dx++;

setXDir( dx );
setYDir( dy );
[/code]
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