Building a 3D game engine from scratch can seem like a daunting task, but with the right tools and knowledge, it can be a rewarding experience. In this article, we will explore how to build a 3D game engine with Java and OpenGL.

What is OpenGL?

OpenGL is an open-source graphics library that provides a set of APIs for rendering 2D and 3D graphics. It is widely used in the gaming industry and is supported by most operating systems. OpenGL provides a low-level interface for accessing graphics hardware, allowing developers to create high-performance graphics applications.

Setting up the Environment

Before we start building our game engine, we need to set up our environment. We will be using the LWJGL library, which provides bindings for OpenGL, OpenAL, and GLFW. We will also be using Gradle as our build tool.

To get started, create a new Gradle project and add the following dependencies to your build.gradle file:

dependencies {
    implementation 'org.lwjgl:lwjgl:3.2.3'
    implementation 'org.lwjgl:lwjgl-glfw:3.2.3'
    implementation 'org.lwjgl:lwjgl-opengl:3.2.3'
}

Next, create a new Java class called GameEngine and add the following code:

import org.lwjgl.glfw.GLFW;
import org.lwjgl.opengl.GL;
import org.lwjgl.opengl.GL11;

public class GameEngine {
    private long window;

    public void run() {
        init();
        loop();
        cleanup();
    }

    private void init() {
        GLFW.glfwInit();
        GLFW.glfwWindowHint(GLFW.GLFW_CONTEXT_VERSION_MAJOR, 3);
        GLFW.glfwWindowHint(GLFW.GLFW_CONTEXT_VERSION_MINOR, 2);
        GLFW.glfwWindowHint(GLFW.GLFW_OPENGL_PROFILE, GLFW.GLFW_OPENGL_CORE_PROFILE);
        GLFW.glfwWindowHint(GLFW.GLFW_OPENGL_FORWARD_COMPAT, GL11.GL_TRUE);
        window = GLFW.glfwCreateWindow(800, 600, "Game Engine", 0, 0);
        GLFW.glfwMakeContextCurrent(window);
        GL.createCapabilities();
    }

    private void loop() {
        while (!GLFW.glfwWindowShouldClose(window)) {
            GLFW.glfwSwapBuffers(window);
            GLFW.glfwPollEvents();
        }
    }

    private void cleanup() {
        GLFW.glfwTerminate();
    }
}

This code initializes GLFW, creates a window, and sets up OpenGL. The loop method runs continuously until the window is closed, swapping the buffers and polling for events.

Rendering 3D Objects

Now that we have our environment set up, we can start rendering 3D objects. We will be using vertex buffers and shaders to render our objects.

First, create a new Java class called Mesh and add the following code:

import org.lwjgl.opengl.GL15;
import org.lwjgl.opengl.GL30;

public class Mesh {
    private int vao;
    private int vbo;
    private int vertexCount;

    public Mesh(float[] vertices) {
        vertexCount = vertices.length / 3;
        vao = GL30.glGenVertexArrays();
        GL30.glBindVertexArray(vao);
        vbo = GL15.glGenBuffers();
        GL15.glBindBuffer(GL15.GL_ARRAY_BUFFER, vbo);
        GL15.glBufferData(GL15.GL_ARRAY_BUFFER, vertices, GL15.GL_STATIC_DRAW);
        GL30.glVertexAttribPointer(0, 3, GL15.GL_FLOAT, false, 0, 0);
        GL15.glBindBuffer(GL15.GL_ARRAY_BUFFER, 0);
        GL30.glBindVertexArray(0);
    }

    public void render() {
        GL30.glBindVertexArray(vao);
        GL15.glBindBuffer(GL15.GL_ARRAY_BUFFER, vbo);
        GL11.glDrawArrays(GL11.GL_TRIANGLES, 0, vertexCount);
        GL15.glBindBuffer(GL15.GL_ARRAY_BUFFER, 0);
        GL30.glBindVertexArray(0);
    }
}

This code creates a new mesh object and initializes the vertex array object (VAO) and vertex buffer object (VBO). The render method binds the VAO and VBO and draws the triangles.

Next, create a new Java class called Shader and add the following code:

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;

import org.lwjgl.opengl.GL20;

public class Shader {
    private int program;

    public Shader(String vertexShaderPath, String fragmentShaderPath) {
        int vertexShader = loadShader(vertexShaderPath, GL20.GL_VERTEX_SHADER);
        int fragmentShader = loadShader(fragmentShaderPath, GL20.GL_FRAGMENT_SHADER);
        program = GL20.glCreateProgram();
        GL20.glAttachShader(program, vertexShader);
        GL20.glAttachShader(program, fragmentShader);
        GL20.glLinkProgram(program);
        GL20.glValidateProgram(program);
    }

    public void use() {
        GL20.glUseProgram(program);
    }

    private int loadShader(String path, int type) {
        StringBuilder shaderSource = new StringBuilder();
        try {
            BufferedReader reader = new BufferedReader(new FileReader(path));
            String line;
            while ((line = reader.readLine()) != null) {
                shaderSource.append(line).append('\n');
            }
            reader.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
        int shader = GL20.glCreateShader(type);
        GL20.glShaderSource(shader, shaderSource);
        GL20.glCompileShader(shader);
        if (GL20.glGetShaderi(shader, GL20.GL_COMPILE_STATUS) == GL11.GL_FALSE) {
            System.err.println("Shader compilation failed!");
            System.err.println(GL20.glGetShaderInfoLog(shader));
            System.exit(1);
        }
        return shader;
    }
}

This code loads the vertex and fragment shaders from files and compiles them into a shader program. The use method sets the shader program to be used for rendering.

Finally, modify the GameEngine class to render a cube using the Mesh and Shader classes:

public class GameEngine {
    private long window;
    private Mesh mesh;
    private Shader shader;

    public void run() {
        init();
        loop();
        cleanup();
    }

    private void init() {
        GLFW.glfwInit();
        GLFW.glfwWindowHint(GLFW.GLFW_CONTEXT_VERSION_MAJOR, 3);
        GLFW.glfwWindowHint(GLFW.GLFW_CONTEXT_VERSION_MINOR, 2);
        GLFW.glfwWindowHint(GLFW.GLFW_OPENGL_PROFILE, GLFW.GLFW_OPENGL_CORE_PROFILE);
        GLFW.glfwWindowHint(GLFW.GLFW_OPENGL_FORWARD_COMPAT, GL11.GL_TRUE);
        window = GLFW.glfwCreateWindow(800, 600, "Game Engine", 0, 0);
        GLFW.glfwMakeContextCurrent(window);
        GL.createCapabilities();

        float[] vertices = {
                // front
                -0.5f, -0.5f,  0.5f,
                 0.5f, -0.5f,  0.5f,
                 0.5f,  0.5f,  0.5f,
                -0.5f,  0.5f,  0.5f,
                // back
                -0.5f, -0.5f, -0.5f,
                 0.5f, -0.5f, -0.5f,
                 0.5f,  0.5f, -0.5f,
                -0.5f,  0.5f, -0.5f,
        };
        mesh = new Mesh(vertices);

        shader = new Shader("vertexShader.glsl", "fragmentShader.glsl");
    }

    private void loop() {
        while (!GLFW.glfwWindowShouldClose(window)) {
            GL11.glClear(GL11.GL_COLOR_BUFFER_BIT | GL11.GL_DEPTH_BUFFER_BIT);
            shader.use();
            mesh.render();
            GLFW.glfwSwapBuffers(window);
            GLFW.glfwPollEvents();
        }
    }

    private void cleanup() {
        mesh.cleanup();
        GLFW.glfwTerminate();
    }
}

This code initializes the mesh and shader objects, and renders the cube in the loop method.

Conclusion

In this article, we explored how to build a 3D game engine with Java and OpenGL. We set up our environment, rendered 3D objects using vertex buffers and shaders, and created a cube using the Mesh and Shader classes. With this knowledge, you can continue to build your own 3D game engine and create amazing games.

Thank you for reading!

Related Articles

No related articles found.

The post How to Build a 3D Game Engine with Java and OpenGL appeared first on Java Master.