Bug: Execution interrupted while drawing

Yes, I think likely what's happening is the IDE uploads the code and then doesn't get a response after a second or so, so it issues a Ctrl-C to break out of it.

You could do:

setTimeout(function() {
  invertCircle(g.getWidth() / 2, g.getHeight() / 2, 30);
}, 1000);

to run the command after a delay so the IDE can upload the code fine and see a response, but then the code happens after.

BUT: iterating over every pixel is always going to be really slow I'm afraid - it's probably not something you want to be doing if there's any way to avoid it. What I'd suggest is actually making two images - one with what you want to draw and one with the circle, and XORing the actual binary data of the image together.

ga = Graphics.createArrayBuffer(176,176,1,{msb:true});
gb = Graphics.createArrayBuffer(176,176,1,{msb:true});
var ba = new Uint32Array(ga.buffer);
var bb = new Uint32Array(gb.buffer);

ga.setFont("Vector:80").drawString("Hello");
gb.fillCircle(40,40,40);

// define this once so JIT only runs once
function xor(a,i) { "jit"
  return a ^ bb[i];
}

function update() {
  var t = getTime();
  E.mapInPlace(ba, ba, xor);
  g.drawImage(ga); // draws with current FG and BG colors
  print("took",getTime()-t,"sec");
}
update();

There are other ways to do it (eg compiled code) but this way a relatively straightforward.

It still takes ~0.4sec to do the entire screen, but if you only wanted part of the screen done then it'd be a bit faster.

I was considering adding different draw styles (add/xor/or/etc) to the Graphics lib which would really help with this, but I'm afraid that isn't implemented yet.