anchor.diff:          let sTexUniform = Gl.GetUniformLocation (samplerShaderProgram, "tex")
   
           let vertexData =
  -            [|-0.5f; -0.5f;
  -              +0.5f; -0.5f;
  -              +0.5f; +0.5f;
  -              -0.5f; +0.5f|]
  +            [|-0.9f; -0.9f;
  +              +0.9f; -0.9f;
  +              +0.9f; +0.9f;
  +              -0.9f; +0.9f|]
           let mutable vertexBuffers = [|0u|]
           Gl.GenBuffers (1, vertexBuffers)
           let vertexBuffer = vertexBuffers.[0]
  
positive.code:             Gl.DisableVertexAttribArray wVertexPos2DAttrib
              Gl.UseProgram 0u
  
              //Gl.BindFramebuffer (Gl.FramebufferTarget.Framebuffer, 0u)
              //Gl.ClearColor (0.0f, 0.0f, 0.0f, 0.0f)
              //Gl.Clear (Gl.ClearBufferMask.ColorBufferBit ||| Gl.ClearBufferMask.DepthBufferBit ||| Gl.ClearBufferMask.StencilBufferBit)
              //Gl.UseProgram whiteShaderProgram
              //Gl.EnableVertexAttribArray sVertexPos2DAttrib
              //Gl.BindBuffer (Gl.BufferTarget.ArrayBuffer, vertexBuffer)
              //Gl.VertexAttribPointer (sVertexPos2DAttrib, 2, Gl.VertexAttribPointerType.Float, false, 2 * sizeof<single>, nativeint 0)
              //Gl.BindBuffer (Gl.BufferTarget.ElementArrayBuffer, indexBuffer)
              //Gl.Uniform1i (sTexUniform, 0) // set attrib to texture slot 0
              //Gl.ActiveTexture 0 // make texture slot 0 active
              //Gl.BindTexture (Gl.TextureTarget.Texture2D, textureFramebufferTexture) // bind texture to slot 0
              //Gl.BindSampler (0u, 0u) // use texture's built-in sampling configuration
              //Gl.DrawElements (Gl.BeginMode.TriangleFan, 4, Gl.DrawElementsType.UnsignedInt, nativeint 0)
              //Gl.DisableVertexAttribArray sVertexPos2DAttrib
              //Gl.UseProgram 0u
  
              SDL.SDL_GL_SwapWindow window
              Threading.Thread.Sleep 16
  
negative.code: 
          while true do
  
              Gl.BindFramebuffer (Gl.FramebufferTarget.Framebuffer, 0u)
              Gl.ClearColor (0.0f, 0.0f, 0.0f, 0.0f)
              Gl.Clear (Gl.ClearBufferMask.ColorBufferBit ||| Gl.ClearBufferMask.DepthBufferBit ||| Gl.ClearBufferMask.StencilBufferBit)
              // 3d rendering...
  
              Gl.BindFramebuffer (Gl.FramebufferTarget.Framebuffer, textureFramebufferTexture)
              Gl.ClearColor (0.0f, 0.0f, 0.0f, 0.0f)
              Gl.Clear (Gl.ClearBufferMask.ColorBufferBit ||| Gl.ClearBufferMask.DepthBufferBit ||| Gl.ClearBufferMask.StencilBufferBit)
              Gl.UseProgram whiteShaderProgram
  