Rendering triangles with OpenTK from VBO

Question

I cannot render triangles for the life of me with a VBO in OpenTK. I am loading my data to the VBO in glControl_Load() event. I get a background screen with no triangles when running. The data is a from a mesh m.OpenGLArrays(out data, out indices) outputs a list of floats and ints. The list of floats for the vertices T1v1, T1v2, T1v3, T2v1, T2v2, T2v3, .... , all three vertices for each triangle back to back.

However given a blank screen with the code when I comment the "intermediate" rendering code everything renders fine....??? What am I doing wrong?

    private void glControl_Load(object sender, EventArgs e)
    {
        loaded = true;
        glControl.MouseMove += new MouseEventHandler(glControl_MouseMove);
        glControl.MouseWheel += new MouseEventHandler(glControl_MouseWheel);

        GL.ClearColor(Color.DarkSlateGray);
        GL.Color3(1f, 1f, 1f);

        m.OpenGLArrays(out data, out indices);
        this.indicesSize = (uint)indices.Length;
        GL.GenBuffers(1, out VBOid[0]);
        GL.GenBuffers(1, out VBOid[1]);

        SetupViewport();
    }

    private void SetupViewport()
    {
        if (this.WindowState == FormWindowState.Minimized) return;
        glControl.Width = this.Width - 32;
        glControl.Height = this.Height - 80;
        Frame_label.Location = new System.Drawing.Point(glControl.Width / 2, glControl.Height + 25);
        GL.MatrixMode(MatrixMode.Projection);
        //GL.LoadIdentity();
        GL.Ortho(0, glControl.Width, 0, glControl.Height, -1, 1); // Bottom-left corner pixel has coordinate (0, 0)
        GL.Viewport(0, 0, glControl.Width, glControl.Height); // Use all of the glControl painting area
        GL.Enable(EnableCap.DepthTest);

        GL.BindBuffer(BufferTarget.ArrayBuffer, VBOid[0]);
        GL.BufferData(BufferTarget.ArrayBuffer, (IntPtr)(data.Length * sizeof(float)), data, BufferUsageHint.StaticDraw);
        GL.BindBuffer(BufferTarget.ArrayBuffer, 0);

        float aspect_ratio = this.Width / (float)this.Height;
        projection = Matrix4.CreatePerspectiveFieldOfView(MathHelper.PiOver4, aspect_ratio, 1, 1024);
        GL.MatrixMode(MatrixMode.Projection);
        GL.LoadMatrix(ref projection);
    }

    private void glControl_Paint(object sender, PaintEventArgs e)
    {
        if (loaded)
        {
            GL.Clear(ClearBufferMask.ColorBufferBit |
                     ClearBufferMask.DepthBufferBit |
                     ClearBufferMask.StencilBufferBit);

            modelview = Matrix4.LookAt(0f, 0f, -200f + zoomFactor, 0, 0, 0, 0.0f, 1.0f, 0.0f);
            var aspect_ratio = Width / (float)Height;
            projection = Matrix4.CreatePerspectiveFieldOfView(MathHelper.PiOver4, aspect_ratio, 1, 512);

            GL.MatrixMode(MatrixMode.Projection);
            GL.LoadMatrix(ref projection);
            GL.MatrixMode(MatrixMode.Modelview);
            GL.LoadMatrix(ref modelview);
            GL.Rotate(angleY, 1.0f, 0, 0);
            GL.Rotate(angleX, 0, 1.0f, 0);

            GL.EnableClientState(ArrayCap.VertexArray);

            GL.BindBuffer(BufferTarget.ArrayBuffer, VBOid[0]);

            GL.Color3(Color.Yellow);

            GL.VertexPointer(3, VertexPointerType.Float, Vector3.SizeInBytes, new IntPtr(0));
            GL.DrawArrays(PrimitiveType.Triangles, 0, data.Length);
            GL.BindBuffer(BufferTarget.ArrayBuffer, 0);
            GL.DisableClientState(ArrayCap.VertexArray);

            //GL.Color3(Color.Yellow);
            //GL.PolygonMode(MaterialFace.Front, PolygonMode.Fill);
            //GL.Begin(PrimitiveType.Triangles);

            //for (int i = 0; i < this.md.mesh.Count; i++)
            //{
            //    GL.Normal3(this.md.mesh[i].normal);
            //    GL.Vertex3(this.md.mesh[i].vertices[0]);
            //    GL.Vertex3(this.md.mesh[i].vertices[1]);
            //    GL.Vertex3(this.md.mesh[i].vertices[2]);
            //}
            //GL.End();
            //GL.EndList();

            glControl.SwapBuffers();

            Frame_label.Text = "Frame: " + frameNum++;
        }
    }

You're using deprecated OpenGL: opengl.org/wiki/Legacy_OpenGL — Felix K.

Jared Bolin Jared Bolin · Accepted Answer · 2015-07-24T06:17:41

If something doesn't seem right, then it probably isn't. I seriously questioned my understanding of opengl and spent hours looking at this. However it was just a simple error of forgetting to iterate a count variable in a for loop to transfer the mesh from one object to another. Each triangle had identical vertices! Always expect the unexpected when it comes to debugging!

Rendering triangles with OpenTK from VBO

1 Answers