I'm sure others have made similar tools, but after using Kirk Israel's playfield pal, and wishing the "missing features" on it were finished, I decided to spend a little time recreating it with some of those features. It's sitting at http://www.tolberts.net/pf.html if anyone is interested.
It's pretty similar to Kirk's, but adds:
- painting by clicking and dragging
- a grid that you can toggle on/off
- you can edit the code or the graphics, and the other immediately updates (and you can paste code in, as long as the height matches what you entered).
- changing the height doesn't erase everything
It's still missing support for different colors though.
Let me know if you play with it and something doesn't work correctly (I wouldn't be surprised if the code parsing is fragile)
(The odd presets -- height of 23 and the left/right bars already filled are what I tend to use on the game I'm working on)