Graphics

float[,] ctrlpoints = new float [4,3] {{ -4.0f, -4.0f, 0.0f }, { -2.0f, 4.0f, 0.0f }, { 2.0f, -4.0f, 0.0f }, { 4.0f, 4.0f, 0.0f }};

private void openGLControl_OpenGLDraw(object sender, RenderEventArgs e)
{
    //  Get the OpenGL object.
    OpenGL gl = openGLControl.OpenGL;

    //  Clear the color and depth buffer.
    gl.Clear(OpenGL.GL_COLOR_BUFFER_BIT | OpenGL.GL_DEPTH_BUFFER_BIT);

    int i;

    gl.Color(1.0f, 1.0f, 1.0f);
    gl.Begin(OpenGL.GL_LINE_STRIP);
    for (i = 0; i <= 30; i++)
    {
        gl.EvalCoord1((float)i / 30.0);
    }
    gl.End();
    // display the control points
    gl.PointSize(5.0f);
    gl.Color(1.0f, 1.0f, 0.0f);
    gl.Begin(OpenGL.GL_POINTS);
    for (i = 0; i < 4; i++)
    {
        gl.Vertex(&ctrlpoints[i][0]);
    }
    gl.End();
    gl.Flush();
}

//(x1,y1)(x2,y2) //original Line
//(x1,y1)(px1,px2) //Perpendicular Line

Orig_Line_Slope = (y1-y2)/(x1-x2);
Recipical_Slope = ((1.0 / Orig_Line_Slope)*-1);

HashLength = 10.0;

px2 = (x1+HashLength);
py2 = (y1+(Orig_Line_Slope*HashLength));

MoveToEx(hdc, x1, y1, NULL);
LineTo(hdc, px2, py2 );