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OpenGL OpenTK. Drawing points by mouse click (port from WebGL)

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Hello,

I try to port this example from WebGL: ch02/ClickedPoints in OpenTK. This example draws the points in position of mouse click.

I draw one point in my example. In beginning the point is drawn in (0, 0.5). Drawing loop is 30 frames per second. When I click on the window area the point must to be redrawn in (0, 0) position.

You can run and test my problem in VS2012 - VS2015: DrawPointsByClick_Problem.zip

VertexShader.glsl

#version 330

in vec4 a_Position;

void main()
{
    gl_Position = a_Position;
    gl_PointSize = 10.0;
}

FragmentShader.glsl

#version 330

out vec4 fragColor;

void main()
{
    fragColor = vec4(0.0, 1.0, 1.0, 1.0);
}

Program.cs

namespace DrawPointsByClick
{
    class Program
    {
        static void Main(string[] args)
        {
            using (var mainWindow = new MainWindow())
            {
                mainWindow.Run(30);
            }
        }
    }
}

MainWindow.cs

using System;
using System.Drawing;
using OpenTK;
using OpenTK.Graphics.OpenGL;
using Utils;
using OpenTK.Input;

namespace DrawPointsByClick
{
    class MainWindow : GameWindow
    {
        private int program;
        private bool canDraw = false;
        private int a_Position;

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

            // Load shaders from files
            string vShaderSource = null;
            string fShaderSource = null;
            ShaderLoader.LoadShader("./Shaders/VertexShader.glsl", out vShaderSource);
            ShaderLoader.LoadShader("./Shaders/FragmentShader.glsl", out fShaderSource);
            if (vShaderSource == null || fShaderSource == null)
            {
                Logger.Append("Failed to load shaders from files");
                return;
            }

            // Initialize the shaders
            if (!ShaderLoader.InitShaders(vShaderSource, fShaderSource, out program))
            {
                Logger.Append("Failed to initialize the shaders");
                return;
            }

            // Get the storage location of a_Position
            a_Position = GL.GetAttribLocation(program, "a_Position");
            if (a_Position < 0)
            {
                Logger.Append("Failed to get the storage location of a_Position");
                return;
            }

            // Pass coordinates of point to a_Position
            GL.VertexAttrib2(a_Position, 0f, 0.5f);

            // Enable Point Size
            GL.Enable(EnableCap.ProgramPointSize);

            // Specify the color for clearing the canvas
            GL.ClearColor(Color.OliveDrab);

            canDraw = true;
        }

        protected override void OnRenderFrame(FrameEventArgs e)
        {
            GL.Viewport(0, 0, Width, Height);
            base.OnRenderFrame(e);

            // Clear the canvas with current color
            GL.Clear(ClearBufferMask.ColorBufferBit);

            if (canDraw)
            {
                // Draw the points
                GL.DrawArrays(PrimitiveType.Points, 0, 1);
            }

            GL.Flush();
            SwapBuffers();
        }

        protected override void OnMouseDown(MouseButtonEventArgs e)
        {
            base.OnMouseDown(e);

            Console.WriteLine("OnMouseDown");

            // Pass coordinates of point to a_Position
            GL.VertexAttrib2(a_Position, 0f, 0f);
        }
    }
}

Utils.cs

using System;
using OpenTK.Graphics.OpenGL;
using System.IO;

namespace Utils
{
    public class ShaderLoader
    {
        ///<summary>
        ///Create a program object and make current
        ///</summary>
        ///<param name="vShader">a vertex shader program</param>
        ///<param name="fShader">a fragment shader program</param>
        ///<param name="program">created program</param>
        ///<returns>
        ///return true, if the program object was created and successfully made current
        ///</returns>
        public static bool InitShaders(string vShaderSource, string fShaderSource, out int program)
        {
            program = CreateProgram(vShaderSource, fShaderSource);
            if (program == 0)
            {
                Logger.Append("Failed to create program");
                return false;
            }

            GL.UseProgram(program);

            return true;
        }

        ///<summary>
        ///Load a shader from a file
        ///</summary>
        ///<param name="errorOutputFileName">a file name for error messages</param>
        ///<param name="fileName">a file name to a shader</param>
        ///<param name="shaderSource">a shader source string</param>
        public static void LoadShader(string shaderFileName, out string shaderSource)
        {
            if (File.Exists(Logger.logFileName))
            {
                // Clear File
                File.WriteAllText(Logger.logFileName, "");
            }

            shaderSource = null;

            using (StreamReader sr = new StreamReader(shaderFileName))
            {
                shaderSource = sr.ReadToEnd();
            }
        }

        private static int CreateProgram(string vShader, string fShader)
        {
            // Create shader object
            int vertexShader = LoadShader(ShaderType.VertexShader, vShader);
            int fragmentShader = LoadShader(ShaderType.FragmentShader, fShader);
            if (vertexShader == 0 || fragmentShader == 0)
            {
                return 0;
            }

            // Create a program object
            int program = GL.CreateProgram();
            if (program == 0)
            {
                return 0;
            }

            // Attach the shader objects
            GL.AttachShader(program, vertexShader);
            GL.AttachShader(program, fragmentShader);

            // Link the program object
            GL.LinkProgram(program);

            // Check the result of linking
            int status;
            GL.GetProgram(program, GetProgramParameterName.LinkStatus, out status);
            if (status == 0)
            {
                string errorString = string.Format("Failed to link program: {0}" + Environment.NewLine, GL.GetProgramInfoLog(program));
                Logger.Append(errorString);
                GL.DeleteProgram(program);
                GL.DeleteShader(vertexShader);
                GL.DeleteShader(fragmentShader);
                return 0;
            }

            return program;
        }

        private static int LoadShader(ShaderType shaderType, string shaderSource)
        {
            // Create shader object
            int shader = GL.CreateShader(shaderType);
            if (shader == 0)
            {
                Logger.Append("Unable to create shader");
                return 0;
            }

            // Set the shader program
            GL.ShaderSource(shader, shaderSource);

            // Compile the shader
            GL.CompileShader(shader);

            // Check the result of compilation
            int status;
            GL.GetShader(shader, ShaderParameter.CompileStatus, out status);
            if (status == 0)
            {
                string errorString = string.Format("Failed to compile {0} shader: {1}", shaderType.ToString(), GL.GetShaderInfoLog(shader));
                Logger.Append(errorString);
                GL.DeleteShader(shader);
                return 0;
            }

            return shader;
        }
    }

    public class Logger
    {
        public static string logFileName = "info.txt";

        /// <summary>
        /// Write a message to a log file
        /// </summary>
        /// <param name="message">a message that will append to a log file</param>
        public static void Append(string message)
        {
            File.AppendAllText(logFileName, message + Environment.NewLine);
        }
    }
}

Edited by 8Observer8

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The solution:
 
1. Open to: C:\Program Files (x86)\Microsoft Visual Studio 12.0\Common7\IDE
2. Right click on devenv.exe.
3. Hover to the "Run with graphics processor..."
4. Select "High-end NVidia processor".
 

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This code draws the point in mouse click position:

protected override void OnMouseDown(MouseButtonEventArgs e)
{
    base.OnMouseDown(e);

    if (e.Button == MouseButton.Left)
    {
        float x = (e.X - Width / 2f) / (Width / 2f);
        float y = -(e.Y - Height / 2f) / (Height / 2f);
        // Pass coordinates of point to a_Position
        GL.VertexAttrib2(a_Position, x, y);

        Console.WriteLine(x + " " + y);
    }
}

Edited by 8Observer8

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