glMakeContextCurrent / glViewport fatal error

Question

I am following a book online on how to get started with GLFW. For reference, I am using Java.

I have written some code by following along with the book, but I am getting this error: FATAL ERROR in native method: Thread[main,5,main]: No context is current or a function that is not available in the current context was called. My code is below:

import org.lwjgl.glfw.GLFW;
import org.lwjgl.opengl.GL11;
import org.lwjgl.system.MemoryUtil;

public class Window {
    private long window;
    
    public Window()
    {
        
    }
    
    public void init()
    {
        GLFW.glfwWindowHint(GLFW.GLFW_CONTEXT_VERSION_MAJOR, 3);
        GLFW.glfwWindowHint(GLFW.GLFW_CONTEXT_VERSION_MINOR, 3);
        GLFW.glfwWindowHint(GLFW.GLFW_OPENGL_PROFILE, GLFW.GLFW_OPENGL_CORE_PROFILE);
        
        if(!GLFW.glfwInit())
        {
            throw new IllegalStateException("Could not initialize glfw");
        }
        
        window = GLFW.glfwCreateWindow(800, 600, "window", MemoryUtil.NULL, MemoryUtil.NULL);
        
        if(window == MemoryUtil.NULL)
        {
            throw new IllegalStateException("Could not initialize window");
        }
        
        GLFW.glfwMakeContextCurrent(window);
        
        GL11.glViewport(0, 0, 800, 600);
        
        GLFW.glfwSetFramebufferSizeCallback(window,  (window, width, height) -> {
            GL11.glViewport(0, 0, width, height);
        });
    }
    
    public void gameLoop()
    {
        while(!GLFW.glfwWindowShouldClose(window))
        {
            GLFW.glfwSwapBuffers(window);
            GLFW.glfwPollEvents();
        }
        
        GLFW.glfwTerminate();
    }
    
    public void cleanup() {
        GLFW.glfwDestroyWindow(window);
    }
}

How should I fix this error? Also, if my code is not structured well, please let me know.

Thanks!

Answer 1

You need GL.createCapabilities() after GLFW.glfwMakeContextCurrent().

This is mentioned in the official sample code (https://www.lwjgl.org/guide).

  // This line is critical for LWJGL's interoperation with GLFW's
  // OpenGL context, or any context that is managed externally.
  // LWJGL detects the context that is current in the current thread,
  // creates the GLCapabilities instance and makes the OpenGL
  // bindings available for use.
  GL.createCapabilities();