// This code was written for the OpenTK library and has been released
// to the Public Domain.
// It is provided "as is" without express or implied warranty of any kind.

#region --- Using directives ---

using System;
using System.Collections.Generic;
using System.Text;
using System.Runtime.InteropServices;
using System.Threading;

using OpenTK;
using OpenTK.Graphics;
using OpenTK.Graphics.OpenGL;
using OpenTK.Platform;
using System.Drawing;

#endregion

namespace Examples.Tutorial
{
    [Example("VBO Static", ExampleCategory.OpenGL, "1.x", 3, Documentation = "VBOStatic")]
    public class T08_VBO : GameWindow
    {
        const float rotation_speed = 180.0f;
        float angle;

        struct Vbo { public int VboID, EboID, NumElements; }
        Vbo[] vbo = new Vbo[2];

        VertexPositionColor[] CubeVertices = new VertexPositionColor[]
        {
                new VertexPositionColor(-1.0f, -1.0f,  1.0f, Color.DarkRed),
                new VertexPositionColor( 1.0f, -1.0f,  1.0f, Color.DarkRed),
                new VertexPositionColor( 1.0f,  1.0f,  1.0f, Color.Gold),
                new VertexPositionColor(-1.0f,  1.0f,  1.0f, Color.Gold),
                new VertexPositionColor(-1.0f, -1.0f, -1.0f, Color.DarkRed),
                new VertexPositionColor( 1.0f, -1.0f, -1.0f, Color.DarkRed), 
                new VertexPositionColor( 1.0f,  1.0f, -1.0f, Color.Gold),
                new VertexPositionColor(-1.0f,  1.0f, -1.0f, Color.Gold) 
        };

        readonly short[] CubeElements = new short[]
        {
            0, 1, 2, 2, 3, 0, // front face
            3, 2, 6, 6, 7, 3, // top face
            7, 6, 5, 5, 4, 7, // back face
            4, 0, 3, 3, 7, 4, // left face
            0, 1, 5, 5, 4, 0, // bottom face
            1, 5, 6, 6, 2, 1, // right face
        };

        public T08_VBO() : base(800, 600) { }

        protected override void OnLoad(EventArgs e)
        {
            base.OnLoad(e);

            Version version = new Version(GL.GetString(StringName.Version).Substring(0, 3));
            Version target = new Version(1, 5);
            if (version < target)
            {
                throw new NotSupportedException(String.Format(
                    "OpenGL {0} is required (you only have {1}).", target, version));
            }

            GL.ClearColor(System.Drawing.Color.MidnightBlue);
            GL.Enable(EnableCap.DepthTest);

            vbo[0] = LoadVBO(CubeVertices, CubeElements);
            vbo[1] = LoadVBO(CubeVertices, CubeElements);
        }

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

            GL.Viewport(0, 0, Width, Height);

            float aspect_ratio = Width / (float)Height;
            Matrix4 perpective = Matrix4.CreatePerspectiveFieldOfView(MathHelper.PiOver4, aspect_ratio, 1, 64);
            GL.MatrixMode(MatrixMode.Projection);
            GL.LoadMatrix(ref perpective);
        }

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

            var keyboard = OpenTK.Input.Keyboard.GetState();
            if (keyboard[OpenTK.Input.Key.Escape])
                this.Exit();
        }

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

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

            Matrix4 lookat = Matrix4.LookAt(0, 5, 5, 0, 0, 0, 0, 1, 0);
            GL.MatrixMode(MatrixMode.Modelview);
            GL.LoadMatrix(ref lookat);

            angle += rotation_speed * (float)e.Time;
            GL.Rotate(angle, 0.0f, 1.0f, 0.0f);

            Draw(vbo[0]);

            SwapBuffers();
        }

        Vbo LoadVBO<TVertex>(TVertex[] vertices, short[] elements) where TVertex : struct
        {
            Vbo handle = new Vbo();
            int size;

            // To create a VBO:
            // 1) Generate the buffer handles for the vertex and element buffers.
            // 2) Bind the vertex buffer handle and upload your vertex data. Check that the buffer was uploaded correctly.
            // 3) Bind the element buffer handle and upload your element data. Check that the buffer was uploaded correctly.

            GL.GenBuffers(1, out handle.VboID);
            GL.BindBuffer(BufferTarget.ArrayBuffer, handle.VboID);
            GL.BufferData(BufferTarget.ArrayBuffer, (IntPtr)(vertices.Length * BlittableValueType.StrideOf(vertices)), vertices,
                          BufferUsageHint.StaticDraw);
            GL.GetBufferParameter(BufferTarget.ArrayBuffer, BufferParameterName.BufferSize, out size);
            if (vertices.Length * BlittableValueType.StrideOf(vertices) != size)
                throw new ApplicationException("Vertex data not uploaded correctly");

            GL.GenBuffers(1, out handle.EboID);
            GL.BindBuffer(BufferTarget.ElementArrayBuffer, handle.EboID);
            GL.BufferData(BufferTarget.ElementArrayBuffer, (IntPtr)(elements.Length * sizeof(short)), elements,
                          BufferUsageHint.StaticDraw);
            GL.GetBufferParameter(BufferTarget.ElementArrayBuffer, BufferParameterName.BufferSize, out size);
            if (elements.Length * sizeof(short) != size)
                throw new ApplicationException("Element data not uploaded correctly");

            handle.NumElements = elements.Length;
            return handle;
        }

        void Draw(Vbo handle)
        {
            // To draw a VBO:
            // 1) Ensure that the VertexArray client state is enabled.
            // 2) Bind the vertex and element buffer handles.
            // 3) Set up the data pointers (vertex, normal, color) according to your vertex format.
            // 4) Call DrawElements. (Note: the last parameter is an offset into the element buffer
            //    and will usually be IntPtr.Zero).

            GL.EnableClientState(ArrayCap.ColorArray);
            GL.EnableClientState(ArrayCap.VertexArray);

            GL.BindBuffer(BufferTarget.ArrayBuffer, handle.VboID);
            GL.BindBuffer(BufferTarget.ElementArrayBuffer, handle.EboID);

            GL.VertexPointer(3, VertexPointerType.Float, BlittableValueType.StrideOf(CubeVertices), new IntPtr(0));
            GL.ColorPointer(4, ColorPointerType.UnsignedByte, BlittableValueType.StrideOf(CubeVertices), new IntPtr(12));

            GL.DrawElements(PrimitiveType.Triangles, handle.NumElements, DrawElementsType.UnsignedShort, IntPtr.Zero);
        }

        /// <summary>
        /// Entry point of this example.
        /// </summary>
        [STAThread]
        public static void Main()
        {
            using (T08_VBO example = new T08_VBO())
            {
                Utilities.SetWindowTitle(example);
                example.Run(30.0, 0.0);
            }
        }
    }
}
