Hello,

I could really use some advice on the following scenario.
It's basically using shapes as compositing masks.

Idea is that Shape A is drawn to screen.
Shape B is then drawn as an alpha channel to A.  Where ever it  is solid, you reveal the background, textures or other shapes through A.

I searched around for awhile, the closest thing I could find is this discussion but it is still using a texture, not another object as the matte...

http://archives.java.sun.com/cgi-bin/wa?A2=ind0207&L=java3d-interest&P=67305

If anyone had ideas it could be a huge help...

---- processing here ----------

import processing.opengl.*;

void setup() {
 size(200, 200, OPENGL);
}

void draw() {

 background(0, 0, 200);
 
 // OBJECT A which is solid
 fill(255,255,255);
 beginShape();
 vertex(30, 20);
 vertex(85, 20);
 vertex(85, 75);
 vertex(30, 75);
 endShape();
 
 // OBJECT B which shold be a mask revealing the background
 fill(255,0,0);
 beginShape();
 vertex(40, 40);
 vertex(60, 60);
 vertex(40, 60);
 endShape();

}

Wow that example is cool.

That one is a bit harder than what I'm trying to do, maybe it's using clipping planes to take out some of the polygons.  

In this case I don't want to punch a hole not with a 3d clipping plane, but just an alpha channel in 2d.  An that alpha is generated using polygons.

http://www.digitalartform.com/archives/2004/10/alpha_channel_a_1.html

http://www.digitalartform.com/assets/fromCG1.jpg

This shows the concept in 2d art:
http://www.luckysquirrel.com/gal_embelshmts/emgal_punc_trees.html

Hope that is more clear,
RoboHaus

The zeitguised stuff is pretty much like what happens when you use the boolean function in 3D packages. I bought a onedotzero book and guessed that that was how he did it. I assumed he took the simple route to making something cool.

What you're suggesting by constantly referring to alpha channels is a mask.

http://processing.org/reference/PImage_mask_.html

To do that you would have to create an offscreen PGraphics object. Draw to it. Then use that PGraphics as a mask for your graphics on screen (g.mask() "g" being the object that holds the graphics being displayed in the applet). Or perhaps do all the drawing in memory and have a PGraphics mask and a PGraphics display. display.mask(). image(mask, 0, 0);

That might slow your work down a shedload.

I've looked for boolean operations on Google but can't find anything. There are numerous threads on creating PGraphics.

just my 2 cents

adm, just posted a playlist over here: http://www.toxi.co.uk/blog/2006/08/my-12-favourite-demos.htm