OpenTK Texturing example

#r "System.Drawing"
#r "OpenTK"
open OpenTK
open OpenTK.Graphics
open OpenTK.Graphics.OpenGL4

let window = new GameWindow (400,400,
                             GraphicsMode.Default, "",
                             GameWindowFlags.Default,
                             DisplayDevice.Default,
                             4, 1, GraphicsContextFlags.ForwardCompatible)

let vao =
    let vao = GL.GenVertexArray()
    GL.BindVertexArray(vao)
    let vbo = GL.GenBuffer()
    GL.BindBuffer(BufferTarget.ArrayBuffer, vbo)
    let data = [|
                //  Position      Color             Texcoords
                -0.5f;  0.5f; 1.0f; 0.0f; 0.0f; 0.0f; 0.0f; // Top-left
                0.5f;  0.5f; 0.0f; 1.0f; 0.0f; 1.0f; 0.0f; // Top-right
                0.5f; -0.5f; 0.0f; 0.0f; 1.0f; 1.0f; 1.0f; // Bottom-right
                -0.5f; -0.5f; 1.0f; 1.0f; 1.0f; 0.0f; 1.0f  // Bottom-left
                |]
    GL.BufferData(BufferTarget.ArrayBuffer,
                  nativeint (4*data.Length), data,
                  BufferUsageHint.StaticDraw)
    
    let ebo = GL.GenBuffer()
    GL.BindBuffer(BufferTarget.ElementArrayBuffer, ebo)
    let elements = [| 0;1;2;2;3;0 |]
    GL.BufferData(BufferTarget.ElementArrayBuffer,
                  nativeint (4 * elements.Length), elements,
                  BufferUsageHint.StaticDraw)
    vao

let vs_source = @"
#version 150 core

in vec2 position;
in vec3 color;
in vec2 texcoord;

out vec2 uv;
void main() {
    uv = texcoord;
    
    gl_Position = vec4(position, 0, 1);
}"
let fs_source = "
#version 150 core

uniform sampler2D tex;

in vec2 uv;

out vec4 col;

void main() {
    col = texture(tex, uv);
}"

let shaderprogram =
    let vs, fs =
        GL.CreateShader(ShaderType.VertexShader),
        GL.CreateShader(ShaderType.FragmentShader)
    GL.ShaderSource(vs, vs_source)
    GL.CompileShader(vs)
    GL.ShaderSource(fs, fs_source)
    GL.CompileShader(fs)
    GL.GetShaderInfoLog(fs) |> printfn "%s"
    GL.GetShaderInfoLog(vs) |> printfn "%s"
    let id = GL.CreateProgram()
    GL.AttachShader(id, vs)
    GL.AttachShader(id, fs)
    GL.LinkProgram(id); GL.UseProgram(id);
    GL.GetProgramInfoLog(id) |> printfn "%s"
    id

let textures =
    let t1, t2 = GL.GenTexture(), GL.GenTexture()
    GL.ActiveTexture(TextureUnit.Texture0)
    GL.BindTexture(TextureTarget.Texture2D, t1)
    let r = new System.Random(0)
    let data = Array.init 10000 (fun i -> r.Next())
    GL.TexImage2D(TextureTarget.Texture2D, 0,
                  PixelInternalFormat.Rgba, 100, 100, 0,
                  PixelFormat.Rgba, PixelType.UnsignedByte, data);
    GL.TexParameter(TextureTarget.Texture2D,
                    TextureParameterName.TextureMinFilter,
                    (float32 TextureMinFilter.Nearest))
    GL.TexParameter(TextureTarget.Texture2D,
                    TextureParameterName.TextureMagFilter,
                    (float32 TextureMagFilter.Nearest))
    let pos = GL.GetAttribLocation(shaderprogram, "position")
    GL.EnableVertexAttribArray(pos)
    GL.VertexAttribPointer(pos, 2, VertexAttribPointerType.Float,
                           false, 7 * 4, (nativeint 0));

    let col = GL.GetAttribLocation(shaderprogram, "color")
    GL.EnableVertexAttribArray(col)
    GL.VertexAttribPointer(pos, 3, VertexAttribPointerType.Float,
                           false, 7 * 4, (nativeint 8));

    let tex = GL.GetAttribLocation(shaderprogram, "texcoord")
    GL.EnableVertexAttribArray(tex)
    GL.VertexAttribPointer(tex, 2, VertexAttribPointerType.Float,
                           false, 7 * 4, (nativeint (5 * 4)));

let render e =
    GL.ClearColor(Color4.Gray)
    GL.Clear(ClearBufferMask.ColorBufferBit)

    GL.DrawElements(PrimitiveType.Triangles, 6,
                    DrawElementsType.UnsignedInt,
                    (nativeint 0))

    window.SwapBuffers()

window.RenderFrame.Add render
window.Run()