Hello,
I have few more questions concerning GLGraphics

1] How it is possible to erase  GLGraphics or GLGraphicsOffScreen?
.getTexture().clear() does not work like I expected:

Code:

import processing.opengl.*;
import codeanticode.glgraphics.*;
import codeanticode.protablet.*;

GLGraphicsOffScreen buf;
GLTexture tex;

void setup()
{
size(600, 600, GLConstants.GLGRAPHICS);  
buf = new GLGraphicsOffScreen(this, width, height, true, 4);
tex = buf.getTexture();

  buf.beginDraw();
  
  // Paint what should be erased
  buf.fill(0,255);  
  buf.ellipse(100,100,50,50);

  //try to erase buf
  tex.setValue(0,0,0,0);
  tex.clear(0,0,0,0);
  
  buf.endDraw();

image(buf.getTexture(), 0, 0, width, height);
// Hey, die, you damn circle !!!
}
 

It does nothing. I think the trouble is that getTexture() return copy of GLgraphics texture not pointer to actual object. clear() clears "tex" but not content of buf.

2] Are render modes for setBlendMode() documented somewhere?
is it possible to activate aditive, substractive or maximum blend mode?
Isn't it possible just pass original opengl glBlendFunc(); and glBlendEquation() into GLGraphics?

3]Is there allready some functionality to set Alpha channel?
I'd like to use it for loading Brush stencils from Black&White pictures. (Use White as transparent and black as opaque)

I'm very happy for your fast answer.
If I use gettexture().clear() outside beginDraw() ... endDraw() it clears something but picture resurect when I start drawing again. I don't understand this behaviour.

This code illustrate it:
Code:

import processing.opengl.*;
import codeanticode.glgraphics.*;
import codeanticode.protablet.*;

GLGraphicsOffScreen buf;
GLTexture tex;

void setup()
{
  size(600, 600, GLConstants.GLGRAPHICS); 
  buf = new GLGraphicsOffScreen(this, width, height, true, 4);
  buf.beginDraw();
  buf.noStroke();
  buf.endDraw();
}

//set color of stroke
void mousePressed(){
  buf.beginDraw();
  buf.fill(random(255),random(255),random(255),128);
  buf.endDraw();
};


//paint the stroke
void mouseDragged(){
 buf.beginDraw();
 buf.ellipse(mouseX,mouseY,50,50);
 buf.endDraw();
};

//clear the stroke from buffer buf
void mouseReleased(){
  buf.getTexture().clear(0,0,0,0);
};

void draw(){
 //some strips as background 
 background(255,255);
 stroke(0);
 for(int i=0;i<width;i+=10){
 line(i,0,i,height);
 };
  
 //view buffer buf 
 image(buf.getTexture(), 0, 0, width, height);
};
 

I hope the behaviour with your version of Glgraphics (I downloaded the glgraphics-20091116 you linked here) is the same as mine.

If you press mouse button and drag the mouse stroke is painted. When you release musebutton it should clear the buffer. Until you press the mouse again everything looks OK. But after the next stroke is started the old stroke returns form the hell.

Hey, I found the problem with clearing the texture of the offscreen surface. It happens when you use antialising, because in that mode there are actually two color buffers used to render the offscreen image, one is the texture that you get with buf.getTexture(), but then there is another one used to generate the downsampling, which doesn't have public access. Doing buf.getTexture().clear(0, 0, 0, 0); only updates the former. So I added a GLGraphicsOffScreen.clear() method that take the same arguments as GLTexture.clear() but clears both buffers:

Code:

import processing.opengl.*;
import codeanticode.glgraphics.*;

GLGraphicsOffScreen buf;
GLTexture tex;

void setup() {
  size(600, 600, GLConstants.GLGRAPHICS); 
  buf = new GLGraphicsOffScreen(this, width, height, true, 4);
  buf.beginDraw();
  buf.noStroke();
  buf.endDraw();
}

void mousePressed(){
  buf.beginDraw();
  buf.fill(random(255),random(255),random(255),128);
  buf.endDraw();
};

void mouseDragged(){
 buf.beginDraw();
 buf.ellipse(mouseX,mouseY,50,50);
 buf.endDraw();
};

void mouseReleased(){
  buf.beginDraw();
  buf.clear(0, 0, 0, 0);
  buf.endDraw();  
};

void draw(){
 //some strips as background 
 background(255,255);
 stroke(0);
 for(int i=0;i<width;i+=10){
 line(i,0,i,height);
 };
  
 image(buf.getTexture(), 0, 0, width, height);
};
 

The copy texture method would also be a good addition to GLTexture, so I prepared this new version that incorporates GLGraphicsOffScreen.clear() and GLTexture.copy():

http://users.design.ucla.edu/~acolubri/processing/glgraphics/glgraphics-20091213.zip