Minimal Java OpenGL example with LWJGL: displays window with red background

MyGame.java

import org.lwjgl.Version;
import org.lwjgl.opengl.GL;

import static org.lwjgl.glfw.Callbacks.glfwFreeCallbacks;
// glfwCreateWindow, etc.
import static org.lwjgl.glfw.GLFW.*;
// GL_COLOR_BUFFER_BIT, etc.
import static org.lwjgl.opengl.GL11.*;
import static org.lwjgl.system.MemoryUtil.NULL;

// java -XstartOnFirstThread -cp lwjgl-release-3.3.3-custom/lwjgl.jar:lwjgl-release-3.3.3-custom/lwjgl-natives-macos.jar:lwjgl-release-3.3.3-custom/lwjgl-glfw.jar:lwjgl-release-3.3.3-custom/lwjgl-glfw-natives-macos.jar:lwjgl-release-3.3.3-custom/lwjgl-opengl.jar:lwjgl-release-3.3.3-custom/lwjgl-opengl-natives-macos.jar MyGame.java
//
// https://www.lwjgl.org/customize
// * ZIP Bundle
// * Minimal OpenGL
// * macOS x64
//
// See also https://github.com/LWJGL/lwjgl3-demos/tree/main/src/org/lwjgl/demo/intro
// Provides justification for every compontent in basic example
public class MyGame {
	public static void main(String[] args) {
		System.out.println("Hello LWJGL " + Version.getVersion() + "!");

		if (!glfwInit())
			throw new IllegalStateException("Unable to initialize GLFW");

		long window = glfwCreateWindow(300, 300, "Hello World!", NULL, NULL);
		if (window == NULL)
			throw new RuntimeException("Failed to create the GLFW window");

		glfwMakeContextCurrent(window);
		glfwSwapInterval(1);
		glfwShowWindow(window);

		GL.createCapabilities();
		glClearColor(1.0f, 0.0f, 0.0f, 0.0f);

		int x = 0;
		int delta = 1;

		// game loop
		while (!glfwWindowShouldClose(window)) {
			glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

			/*
			glBegin(GL_QUADS); 
			glVertex2f(-0.5f, 0.5f);
			glVertex2f(0.5f, 0.5f);
			glVertex2f(0.5f, -0.5f);
			glVertex2f(-0.5f, -0.5f);
			glEnd();
			*/

			if (x > 290)
				delta = -1;

			if (x < 0)
				delta = 1;

			x += delta;

			glColor3f(100, 100, 100);
			drawRectangle(x, 0, 10, 10);

			glColor3f(0, 155, 155);
			drawRectangle(100, 100, 10, 10);

			glfwSwapBuffers(window);
			glfwPollEvents();
		}

		glfwFreeCallbacks(window);
		glfwTerminate();
	}

	/**
	 * How to test?
	 *
	 * Unit:
	 *  - glVertex2f called expected number of times, in order with expected arguments
	 *
	 * Integration:
	 *  - draw rectangle using glVertex2f based method
	 *  - draw the same rectangle using drawRectangle method
	 *  - compare metrices (should match) or sutract matrices and assert result is 0
	 *
	 *  Alternatively: Change Design to make testing easier
	 *   - static Vertex2f[] rectangleVertices(int x, int y, int width, int height);
	 *     - returns list of points (tuples)
	 *   - static void drawVertices(Vertex2f[] vertices, GL_QUADS);
	 *     - humble object pattern (loop over vertices and draws the quad)
	 *
	 */
	private static void drawRectangle(int x, int y, int width, int height) {
		glBegin(GL_QUADS); 
		pixelVertex2i(x, y);
		pixelVertex2i(x + width, y);
		pixelVertex2i(x + width, y + height);
		pixelVertex2i(x, y + height);
		glEnd();
	}

	private static void pixelVertex2i(int x, int y) {
		glVertex2f(pixelPos2Gl(x), pixelPos2Gl(y));
	}

	private static float pixelPos2Gl(int i) {
		return -1.0f + (float) i * (2.0f / 300.0f) + (1.0f / 300.0f);
	}
}