Hey guys, I'm kind of new (to programming and processing). I'm trying to find a way to display only part of an image, and change the amount you can see. I know the image and the mask image (or alpha... i'm not sure what the difference is) need to be the same size, but I didn't know if you could change that while the program's running. I tried using the alpha method I found in the reference, but the program told me it's not a method (i'm running 1.0.9).  It wouldn't let me use resize on a mask either. I couldn't find this in the book either so I didn't know if I was missing something or if this isn't possible.

Code:

void display()   
  {

    xDirector();

    int g= (thisSize/2);

    pushMatrix(); 

    thisCurrentX += Xdirection;
    thisCurrentY += Ydirection;

    translate(thisCurrentX, thisCurrentY);

    rotate(rotationTotal); 
    rotationTotal += rotationRate;
    cat.mask(dotMask[dotShape]);
    dotMask[dotShape].resize(thisSize, thisSize);
    image(cat, -g, -g, thisSize, thisSize);
    

    popMatrix();

  } 

you can use copy http://processing.org/reference/copy_.html
to do that.