JOGL - Pre Defined Shapes

In the Previous chapters we have learned how draw a shapes such as line, triangle, rhombus using JOGL. We draw lines by passing a predefined field, Gl_lines to glBegin() method.

Other than GL_LINES, the glBegin() method accepts eight more parameters. You can use them to draw different shapes. These are used the same way as GL_LINES.

The following table shows the glBegin() method parameters along with their description −

Sr.No	Parameters and Description
1	GL_LINES Creates each pair of vertices as an independent line segment.
2	GL_LINE_STRIP Draws a connected group of line segments from the first vertex to the last.
3	GL_LINE_LOOP Draws a connected group of line segments from the first vertex to the last, again back to the first.
4	GL_TRIANGLES Treats each triplet of vertices as an independent triangle.
5	GL_TRIANGLE_STRIP Draws a connected group of triangles. One triangle is defined for each vertex presented after the first two vertices.
6	GL_TRIANGLE_FAN Draws a connected group of triangles. One triangle is defined for each vertex presented after the first two vertices.
7	GL_QUADS Treats each group of four vertices as an independent quadrilateral.
8	GL_QUAD_STRIP Draws a connected group of quadrilaterals. One quadrilateral is defined for each pair of vertices presented after the first pair.
9	GL_POLYGON Draws a single, convex polygon. Vertices 1,…,n define this polygon.

Let us see some examples using glBegin() parameters.

Program to draw a Line Strip

import javax.media.opengl.GL2;
import javax.media.opengl.GLAutoDrawable;
import javax.media.opengl.GLCapabilities;
import javax.media.opengl.GLEventListener;
import javax.media.opengl.GLProfile;
import javax.media.opengl.awt.GLCanvas;

import javax.swing.JFrame;

public class LineStrip implements GLEventListener {

   @Override
   public void display(GLAutoDrawable drawable) {
   
      final GL2 gl = drawable.getGL().getGL2();
		
      gl.glBegin (GL2.GL_LINE_STRIP);
      gl.glVertex3f(-0.50f,-0.75f, 0);
      gl.glVertex3f(0.7f,0.5f, 0);
      gl.glVertex3f(0.70f,-0.70f, 0);
      gl.glVertex3f(0f,0.5f, 0);
      gl.glEnd();
   }
   
   @Override
   public void dispose(GLAutoDrawable arg0) {
      //method body
   }
   
   @Override
   public void init(GLAutoDrawable arg0) {
      // method body
   }
   
   @Override
   public void reshape(GLAutoDrawable arg0, int arg1, int arg2, int arg3, int arg4) {
      // method body
   }
   
   public static void main(String[] args) {
   
      //getting the capabilities object of GL2 profile
      final GLProfile profile = GLProfile.get(GLProfile.GL2);
      GLCapabilities capabilities = new GLCapabilities(profile);
      
      // The canvas
      final GLCanvas glcanvas = new GLCanvas(capabilities);
      LineStrip r = new LineStrip();
      glcanvas.addGLEventListener(r);
      glcanvas.setSize(400, 400);
      
      //creating frame
      final JFrame frame = new JFrame ("LineStrip");
      
      //adding canvas to frame
      frame.getContentPane().add(glcanvas);
            
      frame.setSize(frame.getContentPane().getPreferredSize());
      frame.setVisible(true);
      
   }//end of main
	
}//end of classimport javax.media.opengl.GL2;

If you compile and execute the above code, the following output is generated −

Code snippet for display() method to draw a Line Loop

public void display(GLAutoDrawable drawable) {

   final GL2 gl = drawable.getGL().getGL2();
   
   gl.glBegin (GL2.GL_LINE_LOOP);
   
   gl.glVertex3f( -0.50f, -0.75f, 0);
   gl.glVertex3f(0.7f, .5f, 0);
   gl.glVertex3f(0.70f, -0.70f, 0);
   gl.glVertex3f(0f, 0.5f, 0);
   
   gl.glEnd();
}

If you replace the display() method of any of the basic template programs with the above code, compile, and execute it, the following output is generated −

Code snippet for display() method to draw a triangle using GL_TRIANGLES

public void display(GLAutoDrawable drawable) {

   final GL2 gl = drawable.getGL().getGL2();
   
   gl.glBegin(GL2.GL_TRIANGLES);        // Drawing Using Triangles
   
   gl.glVertex3f(0.5f,0.7f,0.0f);       // Top
   gl.glVertex3f(-0.2f,-0.50f,0.0f);    // Bottom Left
   gl.glVertex3f(0.5f,-0.5f,0.0f);      // Bottom Right
   
   gl.glEnd();
}

If you replace the display() method of any of the basic template programs with the above code, compile, and execute it, the following output is generated −

Code snippet for display() method to draw a Triangle Strip

public void display(GLAutoDrawable drawable) {

   final GL2 gl = drawable.getGL().getGL2();
   
   gl.glBegin (GL2.GL_TRIANGLE_STRIP);
   
   gl.glVertex3f(0f,0.5f,0);
   gl.glVertex3f(-0.50f,-0.75f,0);
   gl.glVertex3f(0.28f,0.06f,0);
   gl.glVertex3f(0.7f,0.5f,0);
   gl.glVertex3f(0.7f,-0.7f,0);
   
   gl.glEnd();
}

If you replace the display() method of any of the basic template programs with the above code, compile and execute it, the following output is generated −

Code snippet for display() method to draw a quadrilateral

public void display(GLAutoDrawable drawable) {

   final GL2 gl = drawable.getGL().getGL2();
   
   gl.glBegin(GL2.GL_QUADS);
   
   gl.glVertex3f( 0.0f,0.75f,0);
   gl.glVertex3f(-0.75f,0f,0);
   gl.glVertex3f(0f,-0.75f,0);
   gl.glVertex3f(0.75f,0f,0);
   
   gl.glEnd();
}

If you replace the display() method of any of the basic template programs with the above code, compile, and execute it, the following output is generated −

Code snippet for display() method to draw a polygon

public void display(GLAutoDrawable drawable) {

   final GL2 gl = drawable.getGL().getGL2();
   
   gl.glBegin(GL2.GL_POLYGON);
   
   gl.glVertex3f(0f,0.5f,0f);
   gl.glVertex3f(-0.5f,0.2f,0f);
   gl.glVertex3f(-0.5f,-0.2f,0f);
   gl.glVertex3f(0f,-0.5f,0f);
   gl.glVertex3f(0f,0.5f,0f);
   gl.glVertex3f(0.5f,0.2f,0f);
   gl.glVertex3f(0.5f,-0.2f,0f);
   gl.glVertex3f(0f,-0.5f,0f);
   
   gl.glEnd();
}

If you replace display() method of any of the basic template programs with the above code, compile, and execute it, the following output is generated −