Basic Drawings with OpenGL using C#


The purpose of this paper is to show the functions and elements used to plot basic shapes and implement their transformations.

The line drawing in OpenGL is based on the use of vertices, i.e. if you want to draw a line you must define two vertices (start and end), the line will be drawn according to the connection mode you choose, taking into account each of the vertices defined (GL_LINESGL_POLYGON, etc.) then if we define four vertices and selects as the connection mode "GL_LINES" this may result in 2-line stroke, but if you select "GL_QUADS" will result a square.

OpenGl1.gif

Well, having said this we will proceed with our application. The first thing we do is add our control SimpleOpenGlControl which make our lives easier by not having to follow a series of complicated steps to initialize your work area.

El SimpleOpenGlControl belongs to Tao Framework and if we want to use it we must add a reference to Tao.Platform.Windows.

OpenGl2.gif

SimpleOpenGlControl

Step 1:

public Form1()
        {
            InitializeComponent();

            int height = simpleOpenGlControl1.Height;
            int width = simpleOpenGlControl1.Width;

            simpleOpenGlControl1.InitializeContexts();
            Gl.glViewport(0, 0, width,height);

            Gl.glMatrixMode(Gl.GL_PROJECTION);
            Gl.glLoadIdentity();
            Glu.gluPerspective(45.0f, (double)width / (double)height, 0.01f, 5000.0f);
       
}

double xrot, yrot, zrot = 0;


Initialize our workspace and variables that will control the rotation of our figure
simpleOpenGlControl1.InitializeContexts() Initialize out control context or work area.

Gl.glViewport().-Our work area
Gl.glMatrixMode().-  Specify which matrix is the current matrix
Gl.GL_PROJECTION .- Defines the properties of the camera that views the objects 
Gl.GL_MODELVIEW.- matrix defines how your objects are transformed
Glu.gluPerspective.-  set up a perspective projection matrix

Step 2:

Now we are ready to start drawing.

For this we will use the "Paint" event of the control.

private void simpleOpenGlControl1_Paint(object sender, PaintEventArgs e) // OnPaint event
        {
            Gl.glClear(Gl.GL_COLOR_BUFFER_BIT | Gl.GL_DEPTH_BUFFER_BIT);
//clear buffers to preset values

            Gl.glMatrixMode(Gl.GL_MODELVIEW);
            Gl.glLoadIdentity();                
// load the identity matrix

            Gl.glTranslated(0, 0, -4);          //moves our figure (x,y,z)
            Gl.glRotated(xrot += 0.5, 1, 0, 0); //rotate on x
            Gl.glRotated(yrot += 0.3, 0, 1, 0); //rotate on y
            Gl.glRotated(zrot += 0.2, 0, 0, 1);
//rotate on z

            //face 1
            Gl.glBegin(Gl.GL_LINE_LOOP);    //start drawing GL_LINE_LOOP is the connection mode
           
Gl.glColor3ub(255, 0, 255);
            Gl.glVertex3d(1, 1, -1);
            Gl.glVertex3d(1, -1, -1);
            Gl.glVertex3d(-1, -1, -1);
            Gl.glVertex3d(-1, 1, -1);
            Gl.glEnd();

            //face 2
            Gl.glBegin(Gl.GL_LINE_LOOP);
           
Gl.glColor3ub(0, 255, 255);
            Gl.glVertex3d(-1, -1, -1);
            Gl.glVertex3d(1, -1, -1);
            Gl.glVertex3d(1, -1, 1);
            Gl.glVertex3d(-1, -1, 1);
            Gl.glEnd();

            //face 3
            Gl.glBegin(Gl.GL_LINE_LOOP);
           
Gl.glColor3ub(255, 255, 0);
            Gl.glVertex3d(-1, 1, -1);
            Gl.glVertex3d(-1, -1, -1);
            Gl.glVertex3d(-1, -1, 1);
            Gl.glVertex3d(-1, 1, 1);
            Gl.glEnd();

            //face 4
            Gl.glBegin(Gl.GL_LINE_LOOP);
           
Gl.glColor3ub(0, 0, 255);
            Gl.glVertex3d(1, 1, 1);
            Gl.glVertex3d(1, -1, 1);
            Gl.glVertex3d(1, -1, -1);
            Gl.glVertex3d(1, 1, -1);
            Gl.glEnd();

            //face 5
            Gl.glBegin(Gl.GL_LINE_LOOP);
           
Gl.glColor3ub(0, 255, 0);
            Gl.glVertex3d(-1, 1, -1);
            Gl.glVertex3d(-1, 1, 1);
            Gl.glVertex3d(1, 1, 1);
            Gl.glVertex3d(1, 1, -1);
            Gl.glEnd();

            //face 6
            Gl.glBegin(Gl.GL_LINE_LOOP);
           
Gl.glColor4d(255, 0, 0, 100);
            Gl.glVertex3d(-1, 1, 1);
            Gl.glVertex3d(-1, -1, 1);
            Gl.glVertex3d(1, -1, 1);
           
Gl.glVertex3d(1, 1, 1);
            Gl.glEnd();

        }

OpenGl3.gif

Gl.glTranslated(0, 0, -4);          //moves our figure (x,y,z)
Gl.glRotated(xrot += 0.5, 1, 0, 0); //rotate on x
Gl.glRotated(yrot += 0.3, 0, 1, 0); //rotate on y
Gl.glRotated(zrot += 0.2, 0, 0, 1); //rotate on z

Applies rotation and translation matrix to our figure.


Don't you know what TAO is?
Get in here 
http://tinyurl.com/2d5napd 

You need it to start working with openGL and C#
____________
Thanks to Sam ... Great advice

References:

http://www.fastgraph.com/makegames/3drotation/
http://www.opengl.org/

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