The Mysterious Case of LWJGL glfwPollEvents Blocking libGDX Main Loop on macOS

Are you a game developer using libGDX and LWJGL, and have you stumbled upon a pesky issue where your main loop gets blocked on macOS? Well, you’re not alone! Many developers have fallen victim to this mysterious problem, and today, we’re going to unravel the mystery and provide a solution to this frustrating issue.

What’s happening behind the scenes?

Before we dive into the solution, let’s take a step back and understand the underlying issue. The problem occurs when the `glfwPollEvents()` function from LWJGL’s GLFW library is called repeatedly in the main loop of your libGDX application on macOS. This function is responsible for processing events, such as keyboard and mouse input, and updating the window.

However, on macOS, the `glfwPollEvents()` function can get stuck in an infinite loop, causing your main loop to block indefinitely. This is because the function is waiting for events that never arrive, effectively freezing your application.

The Culprit: macOS’s Event Handling Mechanism

The root of the problem lies in macOS’s event handling mechanism. Unlike Windows and Linux, macOS uses a Run Loop to handle events, which can lead to issues when using GLFW’s event handling mechanism.

When `glfwPollEvents()` is called, it waits for events to be processed by the Run Loop. However, if the Run Loop is not properly initialized or if there are no events to process, the function will block indefinitely.

Solution 1: Use glfwWaitEvents instead of glfwPollEvents

One solution to this problem is to replace `glfwPollEvents()` with `glfwWaitEvents()` in your main loop. `glfwWaitEvents()` will wait for events to be available, but it will not block indefinitely if no events are available.

while (!glfwWindowShouldClose(window)) {
    glfwWaitEvents(); // Replace glfwPollEvents() with glfwWaitEvents()
    // Your game logic here
}

This solution is simple and effective, but it may not be suitable for all applications, especially those that require precise control over event handling.

Solution 2: Create a Custom Event Handling Mechanism

A more robust solution is to create a custom event handling mechanism that integrates with libGDX’s event handling system. This approach requires more effort, but it provides finer control over event handling and can be tailored to your specific needs.

Here’s an example of how you can create a custom event handling mechanism:

import com.badlogic.gdx.ApplicationAdapter;
import com.badlogic.gdx.Gdx;
import com.badlogic.gdx.input.GdxInput;
import org.lwjgl.glfw.GLFW;

public class CustomEventHandling extends ApplicationAdapter {
    private long window;

    @Override
    public void create() {
        window = GLFW.glfwCreateWindow(800, 600, "Custom Event Handling", null, null);
        GLFW.glfwMakeContextCurrent(window);
    }

    @Override
    public void render() {
        // Your game logic here

        // Process events using libGDX's event handling system
        GdxInput.processEvents();

        // Update the window
        GLFW.glfwSwapBuffers(window);
        GLFW.glfwPollEvents();
    }

    @Override
    public void dispose() {
        GLFW.glfwDestroyWindow(window);
    }
}

In this example, we create a custom `ApplicationAdapter` that integrates with libGDX’s event handling system. We use `GdxInput.processEvents()` to process events and `GLFW.glfwPollEvents()` to update the window.

Solution 3: Use a Timer to Limit Event Processing

Another solution is to use a timer to limit the amount of time spent processing events. This approach can help prevent the main loop from blocking indefinitely.

long lastEventTime = System.nanoTime();
while (!glfwWindowShouldClose(window)) {
    long currentTime = System.nanoTime();
    if (currentTime - lastEventTime > 100000000) { // Limit event processing to 100ms
        glfwPollEvents();
        lastEventTime = currentTime;
    }
    // Your game logic here
}

In this example, we use a timer to limit the amount of time spent processing events. We only call `glfwPollEvents()` every 100ms, which helps prevent the main loop from blocking indefinitely.

Conclusion

In conclusion, the issue of `LWJGL glfwPollEvents` blocking the main loop on macOS can be resolved using one of the three solutions mentioned above. By understanding the underlying issue and using a combination of LWJGL and libGDX’s event handling mechanisms, you can create a robust and efficient event handling system for your game or application.

Tips and Tricks

Here are some additional tips and tricks to help you tackle this issue:

• Make sure to initialize the GLFW library properly before creating the window.
• Use `glfwSetErrorCallback()` to set an error callback function to handle errors.
• Use `glfwGetError()` to get the last error code and message.
• Use `GLFW.glfwWaitEventsTimeout()` instead of `GLFW.glfwWaitEvents()` to specify a timeout.

Frequently Asked Questions

Question	Answer
What is the difference between glfwPollEvents and glfwWaitEvents?	glfwPollEvents() blocks indefinitely until events are available, while glfwWaitEvents() waits for events to be available but returns immediately if no events are available.
Why does glfwPollEvents block indefinitely on macOS?	On macOS, the Run Loop can get stuck in an infinite loop if not properly initialized or if there are no events to process.
Can I use glfwWaitEvents() in my main loop?	Yes, you can use glfwWaitEvents() in your main loop, but you may need to adjust the timing and event handling to suit your application’s needs.

We hope this article has provided you with a comprehensive understanding of the issue and solutions to tackle the problem of `LWJGL glfwPollEvents` blocking the main loop on macOS. Happy coding!

Frequently Asked Question

Getting stuck with LWJGL glfwPollEvents blocking your libGDX main loop on macOS? Don’t worry, we’ve got you covered!