I've been trying to create an alpha channel from a PGraphics as follows:

1.         PGraphics pg = createGraphics(640, 950, P2D);
2.         pg.beginDraw();
3.         myRegions[i].draw(this); // draw this shape
4.         pg.endDraw();

Doing this:

1.         PImage img = loadImage("raspberries.jpg");
2.         img.mask(pg);
3.         image(img,0,0);

just draws my mask image. Same for calling img.mask(pg.pixels). Creating a new PImage from the java.awt.Image returned by pg.getImage() is not only needlessly complicated, but has the same result: just the mask show up.

Saving the graphics out to a file and loading it works just as you'd hope:

1. img.mask(loadImage("mask.png"));

But this is hardly an efficient way to do things--and I want to use this technique in real time interaction.

Seems like a useful technique, creating an offscreen buffer with a PGraphics that serves as an alpha channel for  a PImage. I"m sure someone has done it before, but a brief search hasn't turned up the answer.

thanks,

-- Paul