When I spam my controls for my platformer an ArrayIndexOutOfBounds happen.

[Smoll05]

Describe the bug
When I spam jump and crouch so much on my game, an error, "java.lang.ArrayIndexOutOfBoundsException: index 100 out of bounds for length 100," occurs. But a while after the first initialization of the game, when I spam the buttons and controls again, the exception will not happen. A particular scenario is when I move left or right before jumping and crouching; the exception will not occur. Here is the complete error stack trace.

To Reproduce
Steps to reproduce the behavior:

1. Initialize or compile and run the game
2. Spam crouch or jump
3. The error occurs

Expected behavior
I expect no crash will happen just by spamming crouching and jumping.

Runtime info(please complete the following information):
Windows 11

Attach log associated with the bug (can be found in "logs/")

java.lang.ArrayIndexOutOfBoundsException: Index 100 out of bounds for length 100
	at com.almasb.fxgl.entity@17.3/com.almasb.fxgl.physics.box2d.pooling.OrderedStack.pop(OrderedStack.java:34)
	at com.almasb.fxgl.entity@17.3/com.almasb.fxgl.physics.box2d.pooling.DefaultWorldPool.popRot(DefaultWorldPool.java:232)
	at com.almasb.fxgl.entity@17.3/com.almasb.fxgl.physics.box2d.dynamics.joints.RopeJoint.solvePositionConstraints(RopeJoint.java:195)
	at com.almasb.fxgl.entity@17.3/com.almasb.fxgl.physics.box2d.dynamics.Island.solve(Island.java:326)
	at com.almasb.fxgl.entity@17.3/com.almasb.fxgl.physics.box2d.dynamics.World.solve(World.java:423)
	at com.almasb.fxgl.entity@17.3/com.almasb.fxgl.physics.box2d.dynamics.World.step(World.java:279)
	at com.almasb.fxgl.entity@17.3/com.almasb.fxgl.physics.PhysicsWorld.onUpdate(PhysicsWorld.java:176)
	at com.almasb.fxgl.all@17.3/com.almasb.fxgl.app.scene.GameScene.step(GameScene.kt:229)
	at com.almasb.fxgl.all@17.3/com.almasb.fxgl.app.scene.GameScene.onUpdate(GameScene.kt:224)
	at com.almasb.fxgl.scene@17.3/com.almasb.fxgl.scene.Scene.update(Scene.kt:105)
	at com.almasb.fxgl.all@17.3/com.almasb.fxgl.app.MainWindow$update$1.invoke(MainWindow.kt:115)
	at com.almasb.fxgl.all@17.3/com.almasb.fxgl.app.MainWindow$update$1.invoke(MainWindow.kt:115)
	at com.almasb.fxgl.core@17.3/com.almasb.fxgl.core.fsm.StateMachine.runOnActiveStates(StateMachine.kt:69)
	at com.almasb.fxgl.all@17.3/com.almasb.fxgl.app.MainWindow.update(MainWindow.kt:115)
	at com.almasb.fxgl.all@17.3/com.almasb.fxgl.app.FXGLApplication$GameApplicationService.onUpdate(FXGLApplication.kt:426)
	at com.almasb.fxgl.all@17.3/com.almasb.fxgl.app.Engine.loop(Engine.kt:134)
	at com.almasb.fxgl.all@17.3/com.almasb.fxgl.app.Engine.access$loop(Engine.kt:24)
	at com.almasb.fxgl.all@17.3/com.almasb.fxgl.app.Engine$loop$1.invoke(Engine.kt:28)
	at com.almasb.fxgl.all@17.3/com.almasb.fxgl.app.Engine$loop$1.invoke(Engine.kt:28)
	at com.almasb.fxgl.all@17.3/com.almasb.fxgl.app.LoopRunner.frame(LoopRunner.kt:103)
	at com.almasb.fxgl.all@17.3/com.almasb.fxgl.app.LoopRunner.access$frame(LoopRunner.kt:23)
	at com.almasb.fxgl.all@17.3/com.almasb.fxgl.app.LoopRunner$impl$2$1.onTick(LoopRunner.kt:57)
	at com.almasb.fxgl.all@17.3/com.almasb.fxgl.app.AnimationTimerLoop$timer$1.handle(LoopRunner.kt:137)
	at javafx.graphics/javafx.animation.AnimationTimer$AnimationTimerReceiver.lambda$handle$0(AnimationTimer.java:58)
	at java.base/java.security.AccessController.doPrivileged(AccessController.java:400)
	at javafx.graphics/javafx.animation.AnimationTimer$AnimationTimerReceiver.handle(AnimationTimer.java:57)
	at javafx.graphics/com.sun.scenario.animation.AbstractPrimaryTimer.timePulseImpl(AbstractPrimaryTimer.java:356)
	at javafx.graphics/com.sun.scenario.animation.AbstractPrimaryTimer$MainLoop.run(AbstractPrimaryTimer.java:266)
	at javafx.graphics/com.sun.javafx.tk.quantum.QuantumToolkit.pulse(QuantumToolkit.java:571)
	at javafx.graphics/com.sun.javafx.tk.quantum.QuantumToolkit.pulse(QuantumToolkit.java:555)
	at javafx.graphics/com.sun.javafx.tk.quantum.QuantumToolkit.pulseFromQueue(QuantumToolkit.java:548)
	at javafx.graphics/com.sun.javafx.tk.quantum.QuantumToolkit.lambda$runToolkit$11(QuantumToolkit.java:353)
	at javafx.graphics/com.sun.glass.ui.InvokeLaterDispatcher$Future.run(InvokeLaterDispatcher.java:96)
	at javafx.graphics/com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
	at javafx.graphics/com.sun.glass.ui.win.WinApplication.lambda$runLoop$3(WinApplication.java:184)
	at java.base/java.lang.Thread.run(Thread.java:1575)

Additional context / possible fixes
I am using rope joint to join two players together, below are the codes that possibly propagated the error.

initPhysics() - This initialized the rope joint def

protected void initPhysics() {
        super.initPhysics();

        var player1 = getPlayer1();
        var physics1 = player1.getComponent(PhysicsComponent.class);

        var player2 = getPlayer2();
        var physics2 = player2.getComponent(PhysicsComponent.class);

        Body bodyA = physics1.getBody();
        Body bodyB = physics2.getBody();

        FXGL.runOnce(() -> {

            RopeJointDef ropeDef = new RopeJointDef();
            ropeDef.setBodyA(bodyA);
            ropeDef.setBodyB(bodyB);
            ropeDef.localAnchorA.set(0, 0);
            ropeDef.localAnchorB.set(0, 0);
            ropeDef.maxLength = 3.0f;
            ropeDef.setBodyCollisionAllowed(false);

            FXGL.getPhysicsWorld().getJBox2DWorld().createJoint(ropeDef);

        }, Duration.seconds(0.1));
    }

Below is the on the input for the jump

FXGL.getInput().addAction(new UserAction ("Jump1") {
   @Override
    protected void onAction() {
        getControlP1().jump();
    }
}, KeyCode.W);

public void jump() {
    if (!physics.isOnGround()) {
        return;
    }

    physics.setVelocityY(-Constants.JUMP_FORCE);
    state.changeState(JUMP);
}

Below is the code of the crouch

FXGL.getInput().addAction(new UserAction("Crouch1") {
    @Override
    protected void onAction() {
        getControlP1().crouch();
    }

    @Override
    protected void onActionEnd() {
        getControlP1().stand();
    }
}, KeyCode.S);

public void crouch() {
    if (physics.isOnGround() && state.isIn(STAND, WALK)) {
        physics.setVelocityX(0);
        state.changeState(CROUCH);

        if(physics.getBody().getType() != BodyType.STATIC) {
            physics.getBody().setType(BodyType.STATIC);
        }
    }
}

public void stand() {
    state.changeState(STAND);
    if(physics.getBody().getType() == BodyType.STATIC) {
        physics.getBody().setType(BodyType.DYNAMIC);
    }
}

When I crouch, I changed the body of the entity into a STATIC since I don't want no movements, then revert it back to DYNAMIC to freely move it again.

[AlmasB]

Hi,

1. I've skimmed through the RopeJoint code that is causing the exception -- pool.popRot(), implying that some of the rotation objects haven't been pushed back to the pool, creating a leak. However, at the moment, I'm afraid I don't see why that could happen. All of the calls related popRot, pushRot are in joints code, do you have any other joints in your game?

You mentioned that the exception does not occur if you move before jumping/crouching. I wonder if an easy workaround is to add a bit of code that makes the player move briefly, after the game is initialised and ready. The player won't really notice this.

2. If you are not constrained by JDK 17, feel free to switch to latest FXGL 21.1, it might be a bit easier for us to debug. It also has getPhysicsWorld().addRopeJoint(...) to add rope joints easily.

When I crouch, I changed the body of the entity into a STATIC since I don't want no movements, then revert it back to DYNAMIC to freely move it again.

I don't know if box2d allows this change to happen at runtime, but as long as it works appropriately, it's fine.

Let me know how you are getting on.

[AlmasB]

After further investigation, I may have found the culprit. These obtain rotations for use,

FXGL/fxgl-entity/src/main/java/com/almasb/fxgl/physics/box2d/dynamics/joints/RopeJoint.java

Lines 77 to 78 in 610b03d

	final Rotation qA = pool.popRot();
	final Rotation qB = pool.popRot();

and this puts them back:

FXGL/fxgl-entity/src/main/java/com/almasb/fxgl/physics/box2d/dynamics/joints/RopeJoint.java

Line 132 in 610b03d

pool.pushRot(2);

However, if this occurs:

FXGL/fxgl-entity/src/main/java/com/almasb/fxgl/physics/box2d/dynamics/joints/RopeJoint.java

Lines 99 to 106 in 610b03d

	if (m_length > JBoxSettings.linearSlop) {
	m_u.mulLocal(1.0f / m_length);
	} else {
	m_u.setZero();
	m_mass = 0.0f;
	m_impulse = 0.0f;
	return;
	}

Then the method exits early and the two rotation objects are never put back, creating a leak, which ultimately results in the crash you mentioned.

I'll take a look at a fix some time this week, hoping the solution is to just move pushRot() before the length check.

[Smoll05]

Thank you very much for your determination in resolving the problem that I have encountered, Mr. Almas Baim. I greatly appreciate all of the work that you have done, from making a game engine on Java (which helped us in our school project) to even helping with problems like mine.

I'm eager to see how you resolve this issue, and I hope it won't be too difficult for you as well.

[AlmasB]

@Smoll05 the fix is now up. To get the latest build, you can use this:

<dependencies>
    <dependency>
        <groupId>com.github.almasb</groupId>
        <artifactId>fxgl</artifactId>
        <version>25+dev-SNAPSHOT</version>
    </dependency>
</dependencies>

<repositories>
    <repository>
        <id>oss.sonatype.org-snapshot</id>
        <url>https://oss.sonatype.org/content/repositories/snapshots</url>
    </repository>
</repositories>

[Smoll05]

Hello and thank you so much for the quick update. I tried adding the dependency and repository in my project, replacing the old FXGL version. But after adding it, I am now unable to add the requires com.almasb.fxgl.all; in my module-info.java. Do you know any fixes for this?

[AlmasB]

Not sure. If this:

open module app.name {
    requires com.almasb.fxgl.all;
}

doesn't work, try using the latest JDK 24.

[Smoll05]

Thank you very much, everything has been resolved now. I also tried propagating the crash, and it doesn't happen anymore. Mr. Almas Baim, I want to thank you again for your dedication and help. If any problems arise, I will notify you again, and hopefully you will assist me again.