Simple3DModel.cs

using System;
using OpenTK.Mathematics;
using OpenTK.Windowing.Common;
using OpenTK.Windowing.Desktop;
using OpenTK.Graphics.OpenGL4;

namespace Simple3DModel
{
    class Program
    {
        static void Main(string[] args)
        {
            var nativeWindowSettings = new NativeWindowSettings
            {
                Size = new Vector2i(800, 600),
                Title = "Simple 3D Model - Rotating Cube"
            };

            using (var window = new ModelWindow(GameWindowSettings.Default, nativeWindowSettings))
            {
                window.Run();
            }
        }
    }

    class ModelWindow : GameWindow
    {
        private float _rotationAngle;
        private DateTime _lastUpdateTime;

        public ModelWindow(GameWindowSettings gameWindowSettings, NativeWindowSettings nativeWindowSettings)
            : base(gameWindowSettings, nativeWindowSettings)
        {
        }

        protected override void OnLoad()
        {
            base.OnLoad();
            GL.ClearColor(0.2f, 0.3f, 0.3f, 1.0f);
            _lastUpdateTime = DateTime.Now;
        }

        protected override void OnRenderFrame(FrameEventArgs e)
        {
            base.OnRenderFrame(e);

            GL.Clear(ClearBufferMask.ColorBufferBit | ClearBufferMask.DepthBufferBit);

            GL.MatrixMode(MatrixMode.Modelview);
            GL.LoadIdentity();
            GL.Translate(0.0f, 0.0f, -6.0f);
            GL.Rotate(_rotationAngle, Vector3.UnitX);
            GL.Rotate(_rotationAngle, Vector3.UnitY);
            GL.Rotate(_rotationAngle, Vector3.UnitZ);

            DrawCube();

            SwapBuffers();

            DateTime currentTime = DateTime.Now;
            TimeSpan elapsedTime = currentTime - _lastUpdateTime;
            _rotationAngle += (float)elapsedTime.TotalMilliseconds / 100.0f;
            _lastUpdateTime = currentTime;
        }

        private void DrawCube()
        {
            GL.Begin(PrimitiveType.Quads);

            // Front face
            GL.Color3(1.0f, 0.0f, 0.0f);
            GL.Vertex3(-1.0f, -1.0f, 1.0f);
            GL.Vertex3(1.0f, -1.0f, 1.0f);
            GL.Vertex3(1.0f, 1.0f, 1.0f);
            GL.Vertex3(-1.0f, 1.0f, 1.0f);

            // Back face
            GL.Color3(0.0f, 1.0f, 0.0f);
            GL.Vertex3(-1.0f, -1.0f, -1.0f);
            GL.Vertex3(1.0f, -1.0f, -1.0f);
            GL.Vertex3(1.0f, 1.0f, -1.0f);
            GL.Vertex3(-1.0f, 1.0f, -1.0f);
                        // Left face
            GL.Color3(0.0f, 0.0f, 1.0f);
            GL.Vertex3(-1.0f, -1.0f, -1.0f);
            GL.Vertex3(-1.0f, -1.0f, 1.0f);
            GL.Vertex3(-1.0f, 1.0f, 1.0f);
            GL.Vertex3(-1.0f, 1.0f, -1.0f);

            // Right face
            GL.Color3(1.0f, 1.0f, 0.0f);
            GL.Vertex3(1.0f, -1.0f, -1.0f);
            GL.Vertex3(1.0f, -1.0f, 1.0f);
            GL.Vertex3(1.0f, 1.0f, 1.0f);
            GL.Vertex3(1.0f, 1.0f, -1.0f);

            // Top face
            GL.Color3(0.0f, 1.0f, 1.0f);
            GL.Vertex3(-1.0f, 1.0f, -1.0f);
            GL.Vertex3(-1.0f, 1.0f, 1.0f);
            GL.Vertex3(1.0f, 1.0f, 1.0f);
            GL.Vertex3(1.0f, 1.0f, -1.0f);

            // Bottom face
            GL.Color3(1.0f, 0.0f, 1.0f);
            GL.Vertex3(-1.0f, -1.0f, -1.0f);
            GL.Vertex3(-1.0f, -1.0f, 1.0f);
            GL.Vertex3(1.0f, -1.0f, 1.0f);
            GL.Vertex3(1.0f, -1.0f, -1.0f);

            GL.End();
        }

        protected override void OnResize(ResizeEventArgs e)
        {
            base.OnResize(e);

            GL.Viewport(0, 0, Size.X, Size.Y);

            GL.MatrixMode(MatrixMode.Projection);
            GL.LoadIdentity();
            Matrix4 perspectiveMatrix = Matrix4.CreatePerspectiveFieldOfView(MathHelper.PiOver4, (float)Size.X / Size.Y, 1.0f, 100.0f);
            GL.LoadMatrix(ref perspectiveMatrix);
        }
    }
}