I’m about at my wits end, and don’t know where else to turn. My dear lazy­web, please come to my aid before I start crying.

I have a toplevel win­dow. I wish to remove dec­o­ra­tions, place it at a spe­cific point on the screen, and give it a spe­cific size. This arrange­ment is so I can have a sin­gle win­dow cov­er­ing mul­ti­ple mon­i­tors in a xin­erama con­fig­u­ra­tion. This doesn’t seem like it should be so hard.
Doing this over a sin­gle mon­i­tor seems to work just fine, at least with metac­ity. My win­dow hap­pily goes “fullscreen”, cov­er­ing the panel at the top, on the mon­i­tor I expect it to. Then, when try­ing to move_resize it to cover both of my heads, things get bad. Attempt­ing to set it to 3200x1200+0+0 gives me a win­dow which is 2721x1200+1600+0 (the min­i­mum width as per gtk size request, cor­rect height, bad X and cor­rect Y). Note that this is tran­si­tion­ing from one screen to both.
Kwin does a lit­tle bet­ter. Depend­ing on which head I attempt, it may go “fullscreen” on the wrong one ini­tially, but it seems to work after that.

Set­ting this win­dow as override-redirect causes all sorts of more-bogus behav­ior, so I’ve pretty much given up on that. Get­ting a new hint into EWMH for multi-head-fullscreen-windows is the cor­rect thing to do, but I don’t have nearly enough time for that right now, and this has to work with cur­rent (and older…) win­dow man­ager releases.

Help?