如何减少我的Java 2D Platformer的滞后？

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.

Answer 2

I would create your variables outside the method so that it is not being created every time you call that method. The best way to program games is to re-use things instead of destroying and creating because destroying & creating cost a lot of computing power.

Graphics2D g2d = (Graphics2D) g; <---declare it outside your method.

And also try to find redundant conditionals. I saw one where you say (if direction right then ..., else if direction left ...); just say (if direction right then ... else ...). Conditionals do not cost much but when you're calling that conditional 1000 times a second I think it adds up. (idk though, but I do it just in case and for making things fluid)

Where you say setjumpstate(false) it's redundant because no matter what, it is executed - just move it outside the conditional.

Answer 3

First of all, this bit here is a problem:

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

In general, disposing a resource you did not create is probably a bad idea. In this specific case, the Graphics passed into paint() is probably used by all other components in the hierarchy, so this could cause really odd results.

Calling Toolkit.sync() here is I think your attempt to eliminate the tearing you were seeing when moving things in the background. But all that it does is to flush any pending draw instructions. That has no effect here because you are probably drawing to a back-buffered Swing component that will be drawn fully later.

The correct way to eliminate tearing is to perform any updates on the event thread, so that you are not changing the screen data while drawing it. One simple way to implement this would be to have your timer just call repaint() , and have the paint() method call cycle() before doing anything.

For dealing with lag, one solution might be to allow a variable frame rate. Instead of moving everything a fixed distance each frame, calculate the time since the last frame and move everything accordingly.