For calibration purposes, I want to display structured drawings/images in my Processing sketch, and capture a camera's view of that with the Capture package.

By calibration I mean a camera pixel to sketch pixel mapping, so that if a camera frame shows something of interest, I can locate it in my sketch, within a reasonable accuracy.

I believe there is no "immediate" mode drawing in Processing, right?  I.e. no way to force the pixels[] to be displayed in the sketch other than at the end of the draw() proc?

I ask because I'd prefer to draw some pixels, wait for cam.available() (maybe twice), then grab the camera's view of the structured image, in a loop involving at least 20 draw/capture pairs.  

The alternative appears to set up a fairly simple state machine, and in even draws create the drawing, and odd draws capture the camera's image of that drawing.

I suspect this has been done several times, but I didn't find it via searching.  Any pointers?