Drawing A Triangle In Java

JOGL - 3D Triangle

In previous chapter we have seen how to draw 3d shapes, this chapter teaches you how to draw 3d triangle and rotate it.

Below given is the program to draw a 3d triangle an rotate it.

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.media.opengl.glu.GLU;  import javax.swing.JFrame;  import com.jogamp.opengl.util.FPSAnimator;  public class Triangle3d implements GLEventListener {     private GLU glu = new GLU();    private float rtri = 0.0f;           @Override    public void display(GLAutoDrawable drawable) {       final GL2 gl = drawable.getGL().getGL2();        // Clear The Screen And The Depth Buffer       gl.glClear( GL2.GL_COLOR_BUFFER_BIT | GL2.GL_DEPTH_BUFFER_BIT );       gl.glLoadIdentity(); // Reset The View       gl.glTranslatef( -0.5f, 0.0f, -6.0f ); // Move the triangle       gl.glRotatef( rtri, 0.0f, 1.0f, 0.0f );       gl.glBegin( GL2.GL_TRIANGLES );                 //drawing triangle in all dimensions       // Front       gl.glColor3f( 1.0f, 0.0f, 0.0f ); // Red       gl.glVertex3f( 1.0f, 2.0f, 0.0f ); // Top Of Triangle (Front) 		       gl.glColor3f( 0.0f, 1.0f, 0.0f ); // Green       gl.glVertex3f( -1.0f, -1.0f, 1.0f ); // Left Of Triangle (Front) 		       gl.glColor3f( 0.0f, 0.0f, 1.0f ); // Blue       gl.glVertex3f( 1.0f, -1.0f, 1.0f ); // Right Of Triangle (Front)                // Right       gl.glColor3f( 1.0f, 0.0f, 0.0f ); // Red       gl.glVertex3f( 1.0f, 2.0f, 0.0f ); // Top Of Triangle (Right) 		       gl.glColor3f( 0.0f, 0.0f, 1.0f ); // Blue       gl.glVertex3f( 1.0f, -1.0f, 1.0f ); // Left Of Triangle (Right) 		       gl.glColor3f( 0.0f, 1.0f, 0.0f ); // Green       gl.glVertex3f( 1.0f, -1.0f, -1.0f ); // Right Of Triangle (Right)                // Left       gl.glColor3f( 1.0f, 0.0f, 0.0f ); // Red       gl.glVertex3f( 1.0f, 2.0f, 0.0f ); // Top Of Triangle (Back) 		       gl.glColor3f( 0.0f, 1.0f, 0.0f ); // Green       gl.glVertex3f( 1.0f, -1.0f, -1.0f ); // Left Of Triangle (Back) 		       gl.glColor3f( 0.0f, 0.0f, 1.0f ); // Blue       gl.glVertex3f( -1.0f, -1.0f, -1.0f ); // Right Of Triangle (Back)                //left       gl.glColor3f( 0.0f, 1.0f, 0.0f ); // Red       gl.glVertex3f( 1.0f, 2.0f, 0.0f ); // Top Of Triangle (Left) 		       gl.glColor3f( 0.0f, 0.0f, 1.0f ); // Blue       gl.glVertex3f( -1.0f, -1.0f, -1.0f ); // Left Of Triangle (Left) 		       gl.glColor3f( 0.0f, 1.0f, 0.0f ); // Green       gl.glVertex3f( -1.0f, -1.0f, 1.0f ); // Right Of Triangle (Left) 		       gl.glEnd(); // Done Drawing 3d triangle (Pyramid)       gl.glFlush();       rtri += 0.2f;    }        @Override    public void dispose( GLAutoDrawable drawable ) {       //method body    }        @Override    public void init( GLAutoDrawable drawable ) {       //method body    }        @Override    public void reshape( GLAutoDrawable drawable, int x, int y, int width, int height ) { 	       // TODO Auto-generated method stub       final GL2 gl = drawable.getGL().getGL2();       if(height lt;=;)          height = 1; 			       final float h = ( float ) width / ( float ) height;       gl.glViewport( 0, 0, width, height );       gl.glMatrixMode( GL2.GL_PROJECTION );       gl.glLoadIdentity(); 		       glu.gluPerspective( 45.0f, h, 1.0, 20.0 );       gl.glMatrixMode( GL2.GL_MODELVIEW );       gl.glLoadIdentity();    }        public static void main( String[] args ) {           // TODO Auto-generated method stub       final GLProfile profile = GLProfile.get( GLProfile.GL2 );       GLCapabilities capabilities = new GLCapabilities( profile );                 // The canvas       final GLCanvas glcanvas = new GLCanvas( capabilities );       Triangle3d triangle = new Triangle3d(); 		       glcanvas.addGLEventListener( triangle );       glcanvas.setSize( 400, 400 ); 		       final JFrame frame = new JFrame ( "3d Triangle (shallow)" ); 		       frame.getContentPane().add( glcanvas );       frame.setSize( frame.getContentPane().getPreferredSize() );       frame.setVisible( true ); 		       final FPSAnimator animator = new FPSAnimator(glcanvas,300,true);       animator.start();    } 	 }

When you compile and execute the above program, the following output is generated. Here, you have the snapshots of rotating 3D triangle. Since this program does not includes depth test, the triangle is generated hollow.

Triangle 3D

To make the triangle solid, you need to enable depth test by using glEnable(GL_DEPTH_TEST). Enabling the depth buffer gives you a blank screen. This can be cleared by clearing the color using glClear(GL_COLOR_BUFFERBIT | GL_DEPTH_BUFFER_BIT) method. To enable depth test in the init() method or in the glDisplay() method, write the following code −

public void init(GLAutoDrawable drawable) {    final GL2 gl = drawable.getGL().getGL2(); 	    gl.glShadeModel(GL2.GL_SMOOTH);    gl.glClearColor(0f, 0f, 0f, 0f);    gl.glClearDepth(1.0f);    gl.glEnable(GL2.GL_DEPTH_TEST);    gl.glDepthFunc(GL2.GL_LEQUAL);    gl.glHint(GL2.GL_PERSPECTIVE_CORRECTION_HINT, GL2.GL_NICEST);  }

Below given is the Program to draw a 3D triangle with depth test.

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.media.opengl.glu.GLU;  import javax.swing.JFrame;  import com.jogamp.opengl.util.FPSAnimator;  public class Triangledepthtest implements GLEventListener {     private GLU glu = new GLU();    private float rtri = 0.0f;  	    @Override    public void display( GLAutoDrawable drawable ) { 	       final GL2 gl = drawable.getGL().getGL2(); 		       gl.glShadeModel( GL2.GL_SMOOTH );       gl.glClearColor( 0f, 0f, 0f, 0f );       gl.glClearDepth( 1.0f );       gl.glEnable( GL2.GL_DEPTH_TEST );       gl.glDepthFunc( GL2.GL_LEQUAL );       gl.glHint(GL2.GL_PERSPECTIVE_CORRECTION_HINT, GL2.GL_NICEST);        // Clear The Screen And The Depth Buffer       gl.glClear(GL2.GL_COLOR_BUFFER_BIT | GL2.GL_DEPTH_BUFFER_BIT);        gl.glLoadIdentity(); // Reset The View       gl.glTranslatef( -0.5f,0.0f,-6.0f ); // Move the triangle       gl.glRotatef( rtri, 0.0f, 1.0f, 0.0f );       gl.glBegin( GL2.GL_TRIANGLES );         //drawing triangle in all dimensions       //front       gl.glColor3f( 1.0f, 0.0f, 0.0f ); // Red       gl.glVertex3f( 1.0f, 2.0f, 0.0f ); // Top 		       gl.glColor3f( 0.0f, 1.0f, 0.0f ); // Green       gl.glVertex3f( -1.0f, -1.0f, 1.0f ); // Left 		       gl.glColor3f( 0.0f, 0.0f, 1.0f ); // Blue       gl.glVertex3f( 1.0f, -1.0f, 1.0f ); // Right)        //right       gl.glColor3f( 1.0f, 0.0f, 0.0f );       gl.glVertex3f( 1.0f, 2.0f, 0.0f ); // Top 		       gl.glColor3f( 0.0f, 0.0f, 1.0f );       gl.glVertex3f( 1.0f, -1.0f, 1.0f ); // Left 		       gl.glColor3f( 0.0f, 1.0f, 0.0f );       gl.glVertex3f( 1.0f, -1.0f, -1.0f ); // Right        //left       gl.glColor3f( 1.0f, 0.0f, 0.0f );       gl.glVertex3f( 1.0f, 2.0f, 0.0f ); // Top 		       gl.glColor3f( 0.0f, 1.0f, 0.0f );       gl.glVertex3f( 1.0f, -1.0f, -1.0f ); // Left  		       gl.glColor3f( 0.0f, 0.0f, 1.0f );       gl.glVertex3f( -1.0f, -1.0f, -1.0f ); // Right         //top       gl.glColor3f( 0.0f, 1.0f, 0.0f );       gl.glVertex3f( 1.0f, 2.0f, 0.0f ); // Top 		       gl.glColor3f( 0.0f, 0.0f, 1.0f );       gl.glVertex3f( -1.0f, -1.0f, -1.0f ); // Left 		       gl.glColor3f( 0.0f, 1.0f, 0.0f );       gl.glVertex3f( -1.0f, -1.0f, 1.0f ); // Right 		       gl.glEnd(); // Done Drawing 3d triangle (Pyramid)        gl.glFlush();       rtri += 0.2f;    }           @Override    public void dispose( GLAutoDrawable drawable ) {    }        @Override    public void init( GLAutoDrawable drawable ) { 	       final GL2 gl = drawable.getGL().getGL2(); 		       gl.glShadeModel( GL2.GL_SMOOTH );       gl.glClearColor( 0f, 0f, 0f, 0f );       gl.glClearDepth( 1.0f );       gl.glEnable( GL2.GL_DEPTH_TEST );       gl.glDepthFunc( GL2.GL_LEQUAL );       gl.glHint(GL2.GL_PERSPECTIVE_CORRECTION_HINT, GL2.GL_NICEST );    }        @Override    public void reshape(GLAutoDrawable drawable, int x, int y, int width, int height ) { 	       // TODO Auto-generated method stub       final GL2 gl = drawable.getGL().getGL2();       if( height <= 0 )           height = 1; 			       final float h = ( float ) width / ( float ) height;       gl.glViewport( 0, 0, width, height );       gl.glMatrixMode( GL2.GL_PROJECTION );       gl.glLoadIdentity(); 		       glu.gluPerspective( 45.0f, h, 1.0, 20.0 );       gl.glMatrixMode( GL2.GL_MODELVIEW );       gl.glLoadIdentity();    }           public static void main( String[] args ) { 	       // TODO Auto-generated method stub       final GLProfile profile = GLProfile.get( GLProfile.GL2 );       GLCapabilities capabilities = new GLCapabilities( profile ); 		       // The canvas       final GLCanvas glcanvas = new GLCanvas( capabilities );       Triangledepthtest triangledepthtest = new Triangledepthtest(); 		       glcanvas.addGLEventListener( triangledepthtest );       glcanvas.setSize( 400, 400 ); 		       final JFrame frame = new JFrame ( "3d Triangle (solid)" );       frame.getContentPane().add(glcanvas);       frame.setSize( frame.getContentPane().getPreferredSize() );       frame.setVisible( true );       final FPSAnimator animator = new FPSAnimator( glcanvas, 300,true); 		       animator.start();    } 	 }

When you compile and execute the above program, the following output is generated.

Here, you can see the snapshots of a rotating 3D triangle. Since this program includes code for depth test, the triangle is generated solid.

Triangle Depth Test