Question

I am making a 2d platformer in Swing java, and I am wondering how to reduce the lag I get from it. I mean, it doesnt lag too bad but it is noticable that it slows down sometimes. I have a Swing timer ticking at 12 milliseconds, a cycle function, and a paint function.

public void cycle() {
    if (guy.getJumpState() == false) {
        if (canExecuteMovement(0, 4)) {
            onGround = false;
            if (guy.getY() > 300) {
                // if you are in the middle, move the platforms.
                for (int i = 0; i < platformCount; i++) {
                    platform[i].setY(platform[i].getY() - 4);
                }
            } else {
                // or just move the guy if not.
                guy.moveY(4);
            }
        } else {
            onGround = true;
        }
    } else {
        if (canExecuteMovement(0, -8)) {
            if (guy.getY() < 300) {
                // if you are in the middle, move the platforms.
                for (int i = 0; i < platformCount; i++) {
                    platform[i].setY(platform[i].getY() + 8);
                }
            } else {
                // or just move the guy if not.
                guy.moveY(-8);
            }
            jumpCount++;
            if (jumpCount >= 15) {
                jumpCount = 0;
                guy.setJumpState(false);
            }
        } else {
            jumpCount = 0;
            guy.setJumpState(false);
        }
    }

    if (guy.getDirection() == "left") {
        if (canExecuteMovement(-3, 0)) {
            if (guy.getX() < 450) {
                // if you are in the middle, move the platforms.
                for (int i = 0; i < platformCount; i++) {
                    platform[i].setX(platform[i].getX() + 3);
                }
            } else {
                // or just move the guy if not.
                guy.moveX(-3);
            }
        }
    } else if (guy.getDirection() == "right") {
        if (canExecuteMovement(3, 0)) {
            if (guy.getX() > 450) {
                // if you are in the middle, move the platforms.
                for (int i = 0; i < platformCount; i++) {
                    platform[i].setX(platform[i].getX() - 3);
                }
            } else {
                // or just move the guy if not.
                guy.moveX(3);
            }
        }
    }
}


public void paint(Graphics g) {
    super.paint(g); // something important
    Graphics2D g2d = (Graphics2D) g;

    // draw platforms
    for (int i = 0; i < platformCount; i++) {
        if (platform[i].getX() > -50 && platform[i].getX() < 950 && platform[i].getY() > -50 && platform[i].getY() < 650) {
            g2d.drawImage(platform[i].getImage(), platform[i].getX(), platform[i].getY(), this);
        }
    }

    // draw guy
    g2d.drawImage(guy.getImage(), guy.getX(), guy.getY(), this);

    // destroy unneeded processes
    Toolkit.getDefaultToolkit().sync();
    g.dispose();
}

What can I do to optimize this and cause less lag? When I make a thread for the cycle function itself, the platforms sometimes seperate for a split second. I assume because since the thread is asynchronous, half of it is done while the paint function goes on.

Answer 1

Some loose thoughts (it’s been years since I did some animation in Swing), and you didn’t posted some compilable code.

• Have you tried do paintComponent() — paint does a lot of other stuff. And then maybe you need to add repaint() to tick function. Every time I reloaded paint it enden in a mess.
• Also try increasing tick time — youll waste less time repaiting.
• Also I assume you are doing ticks by Timers.
• I have no idea why you dispose graphics object
• Also try just dropping sync (Ive done animations that work on many oeses without it) Toolkit.getDefaultToolkit().sync()

If it doesn’t help use profiler to find a bottleneck. Visual VM is quite nice. Also Visual VM is part of the jdk for some time — just go into bin folder and launch jvisualvm.

EDIT: (thread issues)

• Some people suggested using threads — which I diasgree. If you want do some work outside EDT please use SwingWorker
• I assume you are not calling paint() but just call repeaint(). If you do call paint() (whatever black magic you also make to make it work) please just call repaint() that will schedule repaing on appropriate time.