glBlendEquation — specify the equation used for both the RGB blend equation and the Alpha blend equation
C Specification
void glBlendEquation(GLenum mode);
Parameters
mode
specifies how source and destination colors are combined.
It must be GL_FUNC_ADD, GL_FUNC_SUBTRACT,
GL_FUNC_REVERSE_SUBTRACT, GL_MIN, GL_MAX.
Description of glBlendEquation
The blend equations determine how a new pixel (the ''source'' color)
is combined with a pixel already in the framebuffer (the ''destination''
color). This function sets both the RGB blend equation and the alpha
blend equation to a single equation.
These equations use the source and destination blend factors
specified by either glBlendFunc or glBlendFuncSeparate.
See glBlendFunc or glBlendFuncSeparate for a description of the various blend factors.
Details
Refer to http://www.opengl.org/sdk/docs/man/xhtml/glBlendEquation.xml
Example in Java for glBlendEquation
package glredbook12x;
/**
* Demonstrate the different blending functions available with the OpenGL
* imaging subset. This program demonstrates use of the glBlendEquation() call.
* The following keys change the selected blend equation function: <br>
* <ul>
* <li>'a' -> GL_FUNC_ADD
* <li>'s' -> GL_FUNC_SUBTRACT
* <li>'r' -> GL_FUNC_REVERSE_SUBTRACT
* <li>'m' -> GL_MIN 'x' -> GL_MAX
* </ul>
*
* @author Kiet Le (java port)
*/
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;
import javax.swing.*;
import javax.media.opengl.*;
import javax.media.opengl.glu.*;
public class blendeqn
extends JFrame
implements GLEventListener//
, KeyListener
{
private GLCapabilities caps;
private GLCanvas canvas;
private GLU glu;
private KeyEvent key;
public blendeqn()
{
super("blendeqn");
//
canvas = new GLCanvas();
canvas.addGLEventListener(this);
canvas.addKeyListener(this);
add(canvas);
}
public void run()
{
setSize(512, 512);
setLocationRelativeTo(null);
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
setVisible(true);
canvas.requestFocusInWindow();
}
public static void main(String[] args)
{
new blendeqn().run();
}
public void init(GLAutoDrawable drawable)
{
GL gl = drawable.getGL();
//
gl.glClearColor(1.0f, 1.0f, 0.0f, 0.0f);
gl.glBlendFunc(GL.GL_ONE, GL.GL_ONE);
gl.glEnable(GL.GL_BLEND);
}
public void display(GLAutoDrawable drawable)
{
GL gl = drawable.getGL();
//
gl.glClear(GL.GL_COLOR_BUFFER_BIT);
if (key != null)
{
switch (key.getKeyCode()) {
case KeyEvent.VK_A:
/*
* Colors are added as: (1, 1, 0) + (0, 0, 1) = (1, 1, 1) which will
* produce a white square on a yellow background.
*/
gl.glBlendEquation(GL.GL_FUNC_ADD);
break;
case KeyEvent.VK_S:
/*
* Colors are subtracted as: (0, 0, 1) - (1, 1, 0) = (-1, -1, 1) which
* is clamped to (0, 0, 1), producing a blue square on a yellow
* background
*/
gl.glBlendEquation(GL.GL_FUNC_SUBTRACT);
break;
case KeyEvent.VK_R:
/*
* Colors are subtracted as: (1, 1, 0) - (0, 0, 1) = (1, 1, -1) which
* is clamed to (1, 1, 0). This produces yellow for both the square
* and the background.
*/
gl.glBlendEquation(GL.GL_FUNC_REVERSE_SUBTRACT);
break;
case KeyEvent.VK_M:
/*
* The minimum of each component is computed, as [min(1, 0), min(1,
* 0), min(0, 1)] which equates to (0, 0, 0). This will produce a
* black square on the yellow background.
*/
gl.glBlendEquation(GL.GL_MIN);
break;
case KeyEvent.VK_X:
/*
* The minimum of each component is computed, as [max(1, 0), max(1,
* 0), max(0, 1)] which equates to (1, 1, 1) This will produce a white
* square on the yellow background.
*/
gl.glBlendEquation(GL.GL_MAX);
break;
}
key = null;
}
gl.glColor3f(0.0f, 0.0f, 1.0f);
gl.glRectf(-0.5f, -0.5f, 0.5f, 0.5f);
gl.glFlush();
}
public void reshape(GLAutoDrawable drawable, //
int x, int y, int w, int h)
{
GL gl = drawable.getGL();
//
double aspect = (double) w / (double) h;
gl.glViewport(0, 0, w, h);
gl.glMatrixMode(GL.GL_PROJECTION);
gl.glLoadIdentity();
if (aspect < 1.0)
{
aspect = 1.0 / aspect;
gl.glOrtho(-aspect, aspect, -1.0, 1.0, -1.0, 1.0);
}
else gl.glOrtho(-1.0, 1.0, -aspect, aspect, -1.0, 1.0);
gl.glMatrixMode(GL.GL_MODELVIEW);
}
public void displayChanged(GLAutoDrawable drawable, //
boolean deviceChanged, boolean modeChanged)
{
}
public void keyTyped(KeyEvent e)
{
}
public void keyPressed(KeyEvent e)
{
this.key = e;
switch (e.getKeyCode()) {
case KeyEvent.VK_ESCAPE:
System.exit(0);
break;
}
canvas.display();
}
public void keyReleased(KeyEvent e)
{
}
} Source: Kiet Le's The Red Book Examples using JOGL
