JOGL - Lighting


Advertisements


This chapter explains you how to apply lighting effect to an object using JOGL.

To set lighting, initially enable lighting using the glEnable() method. Then apply lighting for the objects, using the glLightfv(int light, int pname, float[] params, int params_offset) method of GLLightingFunc interface. This method takes four parameters.

The following table describes the parameters of gllightfv() method.

Sr.No. Parameter Name and Description
1

Light

Specifies a light. The number of lights depends on the implementation, but at least eight lights are supported. It accepts ten values, those parameters are discussed in a separate table named Light Source Parameters given below.

2

Pname

Specifies a single valued light source parameter. For light source, there are ten parameters as discussed below.

3

Params

Specifies a pointer to the value or values that is set to the parameter pname of light source light.

4

Light source parameter

You can use any of the light source parameters given below.

Light source parameters

Sr.No. Parameter and Description
1

GL_AMBIENT

It contains the parameters that specify the ambient intensity of the light.

2

GL_DIFFUSE

It contains the parameters that specify the diffuse intensity of the light.

3

GL_SPECULAR

It contains the parameters that specify the specular intensity of the light.

4

GL_POSITION

It contains four integer or floating-point values that specify the position of the light in homogeneous object coordinates.

5

GL_SPOT_DIRECTION

It contains parameters that specify the direction of light in homogeneous object coordinates.

6

GL_SPOT_EXPONENT

Its parameters specify the intensity distribution of light.

7

GL_SPOT_CUTOFF

The single parameter of this specifies the maximum spread angle of the light.

8

GL_CONSTANT_ATTENUATION or GL_LINEAR_ATTENUATION or GL_QUADRATIC_ATTENUATION

You can use any of these attenuation factors, which is represented by a single value.

Lighting is enabled or disabled using glEnable() and glDisable () methods with the argument GL_LIGHTING.

The following template is given for lighting −

gl.glEnable(GL2.GL_LIGHTING); 
gl.glEnable(GL2.GL_LIGHT0);  
gl.glEnable(GL2.GL_NORMALIZE); 

float[] ambientLight = { 0.1f, 0.f, 0.f,0f };  // weak RED ambient 
gl.glLightfv(GL2.GL_LIGHT0, GL2.GL_AMBIENT, ambientLight, 0); 

float[] diffuseLight = { 1f,2f,1f,0f };  // multicolor diffuse 
gl.glLightfv(GL2.GL_LIGHT0, GL2.GL_DIFFUSE, diffuseLight, 0); 

Applying Light to a Rotating Polygon

Follow the given steps for applying light to a rotating polygon.

Rotate the polygon using glRotate() method

gl.glClear(GL2.GL_COLOR_BUFFER_BIT | GL2.GL_DEPTH_BUFFER_BIT); 
  
// Clear The Screen And The Depth Buffer  
gl.glLoadIdentity();  
                 
// Reset The View  
gl.glRotatef(rpoly, 0.0f, 1.0f, 0.0f); 

Let us go through the program to apply light to a rotating polygon −

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; 

import com.jogamp.opengl.util.FPSAnimator; 
 
public class PolygonLighting implements GLEventListener { 
   private float rpoly;
	
   @Override 
	
   public void display( GLAutoDrawable drawable ) {
   
      final GL2 gl = drawable.getGL().getGL2(); 
      gl.glColor3f(1f,0f,0f); //applying red
      
      // 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.glRotatef( rpoly, 0.0f, 1.0f, 0.0f ); 
		
      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(); 
		
      gl.glFlush(); 
      
      rpoly += 0.2f;  //assigning the angle 
      
      gl.glEnable( GL2.GL_LIGHTING );  
      gl.glEnable( GL2.GL_LIGHT0 );  
      gl.glEnable( GL2.GL_NORMALIZE );  

      // weak RED ambient 
      float[] ambientLight = { 0.1f, 0.f, 0.f,0f };  
      gl.glLightfv(GL2.GL_LIGHT0, GL2.GL_AMBIENT, ambient-Light, 0);  

      // multicolor diffuse 
      float[] diffuseLight = { 1f,2f,1f,0f };  
      gl.glLightfv( GL2.GL_LIGHT0, GL2.GL_DIFFUSE, diffuse-Light, 0 ); 
   }  
      
   @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 ); 
      PolygonLighting polygonlighting = new PolygonLighting(); 
      glcanvas.addGLEventListener( polygonlighting ); 
      glcanvas.setSize( 400, 400 ); 

      //creating frame 
      final JFrame frame = new JFrame (" Polygon lighting ");  

      //adding canvas to it 
      frame.getContentPane().add( glcanvas ); 
      frame.setSize( frame.getContentPane().getPreferredSize()); 
      frame.setVisible( true );  
                    
      //Instantiating and Initiating Animator 
      final FPSAnimator animator = new FPSAnimator(glcanvas, 300,true ); 
      animator.start();                     
      
   } //end of main 
	
} //end of class 

If you compile and execute the above program, it generates the following output. Here, you can observe various snapshots of a rotating polygon with lighting.

Polygon Lighting

Advertisements