Question

I’m trying to make a clock-wise rotating triangle, but I can not. I made a timer control but the result is the same without the timer. As a result, the below code does not show rotating triangle.

How can i rotate triangle with CSGL?

namespace WinDrawCoordinate
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private float a = 0.0f;
        private void Form1_Load(object sender, EventArgs e)
        {

            timer1.Start();
        }

        protected void Gosterim()
        {
            GL.glClear(GL.GL_COLOR_BUFFER_BIT);
            GL.glLoadIdentity();
            Hesapla();
            Ucgen();

        }
        protected void ayarlar()
        {
            GL.glClearColor(1, 1, 1, 1);
            GL.glShadeModel(GL.GL_FLAT);
        }
        protected void Hesapla()
        {
            a += 0.5f;
            this.Refresh();
        }

        protected void Ucgen()
        {
            GL.glColor3f(0, 1, 1);
            GL.glRotatef(a, 0, 0, -1);
            GL.glBegin(GL.GL_TRIANGLES);
            GL.glVertex2f(-0.2f, -0.2f);
            GL.glVertex2f(0.2f, -0.2f);
            GL.glVertex2f(0.0f, 0.2f);
            GL.glEnd();
        }

        private void timer1_Tick(object sender, EventArgs e)
        {
            ayarlar();

            Gosterim();
        }
    }

Answer 1

From the code posted I see a couple things:

1. You don’t have any matrix set-up. While you can use the default matrices you should almost certainly specify your own to ensure the triangle is where you expect. The default matrices should work for you here as they specify an identity modelview and projection.

2. You don’t have a call to swap buffers. You need a call after you’re done drawing to swap the front and back buffers so that the triangle is displayed. For CsGL I think there is a SwapBuffer() method you can use.

3. Don’t use a timer to pump your redrawing. Timers work unreliably as they use the windows message pump and they are hard to get good results from. Instead you should use a render loop–a loop that runs the entire time your program runs and just keeps refreshing the screen. You have to make sure you give the operating system time to handle your messages though. A very simple render loop might be:

   void RenderLoop() {
     while (true) {
       SetUpCamera();
       CreateGeometry();
       SwapBuffers();
       Application.DoEvents(); // this lets windows process messages
     }
   }
   

   note that there are better ways to get a good message loop in C# but this is easy to set up and reason about.