The following description is derived from my experience getting MozPlugger to work in Firefox to display PDF files using Evince.
Swallowing Message Flow
X Windows uses messages for communication between programs and the X Server. Messages are queued for each program and read at the programs leisure.
- Firefox registers for root window notitications, then starts Evince.
- Evince creates its main window and asks X Server to display it.
- X Server passes the display request to Window Manager.
- Window Manager assumes control of Evinces main window.
- Firefox requests that Window Manager relinquish control of Evinces main window.
- Firefox requests control of Evinces main window.
- Firefox gains control and moves and resizes Evinces main window to fit in a tab.
- FF -> XSelectInput(wXS, SubstructureNotifyMask)
- FF -> Exec(EV)
- EV -> XCreateWindow(wEV) -> XS
- XS -> CreateNotify\[w?] -> FF
- FF -> Save w? (Note: FF doesn't know yet which window is wEV)
- EV -> XMapWindow(wEV) -> XS
- XS -> MapRequest\[wEV] -> WM
- WM -> XReparentWindow(wEV, parent: wXS -> wWM) -> XS
- WM -> XChangeProperty(wEV, WM_STATE = Normal) -> XS
- XS -> ReparentNotify\[wEV, parent: wXS -> wWM] -> FF
- FF -> Locate wEV in w?s
- FF -> XSelectInput(wEV, SubstructureNotifyMask | PropertyChangeMask)
- FF -> If WM_STATE != Withdrawn: XWithdrawWindow(wEV) -> XS
- XS -> PropertyNotify\[wEV, WM_STATE = Normal] -> FF (Note: This may not be seen by FF, depending on timing)
- FF -> If wEV not withdrawn above: XWithdrawWindow(wEV) -> XS
- XS -> ReparentNotify\[wEV, parent: wWM -> wXS] -> FF
- FF -> XReparentWindow(wEV, parent: wXS -> wFF) -> XS
- XS -> ReparentNotify\[wEv, parent: wXS -> wFF] -> FF
- FF-> XMoveResizeWindow(wEv)
- Because the messaging system is asynchronous, the PropertyNotify of wEVs WM_STATE change to Normal may come before FF is listening for PropertyNotifiy on wEV. In that case, FF checks wEVs WM_STATE in the initial ReparentNotify.