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Vertex/Color pointers issue

Posted Monday, 23 August, 2010 - 05:34 by Dr_Asik in

I'm just learning how to use vertex pointers, and I'm having a weird issue with OpenTK. I'm just trying to display a red-blue-green triangle in a GameWindow, with this code:

       protected override void OnRenderFrame(FrameEventArgs e) {
            GL.Clear(ClearBufferMask.ColorBufferBit | ClearBufferMask.DepthBufferBit);
            GL.MatrixMode(MatrixMode.Projection);
            GL.LoadIdentity();
            var matrix = Matrix4.CreatePerspectiveFieldOfView((float)(Math.PI / 4.0), 1.3333f, 1, 1000);
            GL.LoadMatrix(ref matrix);
            GL.MatrixMode(MatrixMode.Modelview);
            GL.LoadIdentity();
 
            var vertices = new float[] { 0.0f, 1.0f, -10.0f, -1.0f, -1.0f, -10.0f, 1.0f, -1.0f, -10.0f };
            var colors = new float[] { 1.0f, 0.0f, 0.0f, 0.0f, 1.0f, 0.0f, 0.0f, 0.0f, 1.0f };
 
            GL.EnableClientState(ArrayCap.VertexArray);
	    GL.EnableClientState(ArrayCap.ColorArray);
 
            GL.ColorPointer(3, ColorPointerType.Float, 0, colors);
            GL.VertexPointer(3, VertexPointerType.Float, 0, vertices);
	    GL.DrawArrays(BeginMode.Triangles, 0, 3);
 
            GL.DisableClientState(ArrayCap.VertexArray);
            GL.DisableClientState(ArrayCap.ColorArray);
 
            SwapBuffers();
        }

The problem is, the vertex that is supposed to be red appears black instead. I've translated the code in C++ and it displays fine. Here's how it looks like with OpenTK:

Here's the equivalent native OpenGL code and the result: 

#include <GL/freeglut.h>
 
float vertices[] = { 0.0f, 1.0f, -10.0f, -1.0f, -1.0f, -10.0f, 1.0f, -1.0f, -10.0f };
float colors[] = { 1.0f, 0.0f, 0.0f, 0.0f, 1.0f, 0.0f, 0.0f, 0.0f, 1.0f };
 
void render() {
	glMatrixMode(GL_PROJECTION);
	glLoadIdentity();
	gluPerspective(45.0, 1.3333, 1, 1000);
	glMatrixMode(GL_MODELVIEW);
	glLoadIdentity();		
 
	glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT);
 
	glEnableClientState(GL_VERTEX_ARRAY);
	glEnableClientState(GL_COLOR_ARRAY);
 
	glColorPointer(3, GL_FLOAT, 0, colors);
	glVertexPointer(3, GL_FLOAT, 0, vertices);
	glDrawArrays(GL_TRIANGLES, 0, 3);
 
	glDisableClientState(GL_VERTEX_ARRAY);
	glDisableClientState(GL_COLOR_ARRAY);
 
	glutSwapBuffers();
 
}
 
int main(int argc,char *argv[])
{
	glutInit(&argc, argv);
	glutInitDisplayMode(GLUT_RGB | GLUT_DEPTH | GLUT_DOUBLE);
	glutInitWindowSize(800, 600);
	glutCreateWindow("test");
	glutDisplayFunc(render);
	glutMainLoop();
	return EXIT_SUCCESS;
}

I am using the OpenTK Branch 1.0 revision 2713 (latest at the time of writing this).

‹ Getting the OpenTK.GLControl HDC Vertex/Color pointers issue ›

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Dr_Asik's picture

Re: Vertex/Color pointers issue

Posted Monday, 23 August, 2010 - 05:58 by Dr_Asik

Ok so I've nailed it down to calling InitTexturing() on the class TexUtil from TexLib. This is what the function does:

    public static void InitTexturing()
    {
      GL.Disable(EnableCap.CullFace);
      GL.Enable(EnableCap.Texture2D);
      GL.Enable(EnableCap.Blend);
      GL.BlendFunc(BlendingFactorSrc.SrcAlpha, BlendingFactorDest.OneMinusSrcAlpha);
      GL.PixelStore(PixelStoreParameter.UnpackAlignment, 1);
    }

So if I disable Texture2D, rendering looks fine again. Guess I just solved my own problem. :P