At the moment, these mockups only show three tabs:
Local Tab - controls local login appearance
Remote Tab - controls remote login appearance
Accessibility Tab - controls accessibility features
I haven't ruled out the possibility of retaining all the other configuration features in this dialog too, but if we decide to split it into two dialogs, this constitutes my first best-guess at what should go in the "end user" one.
The Style dropdown at the top of the Local tab offers the option of Themed, Plain, or Plain with Face Browser. (I've used Plain since I think it would be good to remove the term 'Gtk theme' from the dialog.) The contents of the tab differ depending on whether Themed or one of the two Plain options is selected, so I'll deal with them separately.
I believe we should aim to make theme selection as close as possible to the desktop theme and background selection experience, so this looks quite a lot different from the current theme selection tab. There should be plenty of code from gnome-control-center to borrow, though :)
The Theme dropdown offers the choice of Selected Only or Random from Selected. When Selected Only is chosen, the theme list below it is single-select only. When Random from Selected is chosen, the list becomes multi-selectable, and the theme shown at login time is chosen randomly from the selected themes.
The theme selection list is identical to that in the desktop theme manager et al.; a thumbnail on the left, the name of the theme in large bold on the right, with its description below in regular font. The author and copyright information for the theme are shown to the right of the list.
The Install and Remove buttons behave as they do now. (The mockup obviously doesn't show the correct button icons.)
The Welcome Message section allows the user to choose the standard (locale-friendly) welcome message for local logins, or to type their own, which will not be localised of course.
Allow system administrator to log in determines whether root is allowed to log in locally via gdm.
The Background section allows the user to set a background colour if desired, and/or a background image, when using the gtk theme. Colours are selected using the standard GNOME colour button, image files using the standard GNOME file chooser button (wrongly shown as a dropdown list in this mockup-- the arrow should be a folder icon). Scale to fit screen is enabled only when Image is checked. The thumbnail on the left should reflect all three settings; i.e., unless Scale to fit screen is selected, there should be a border around the thumbnail of the image, filled with the selected colour.
(Note: IIRC there's one combination of background/colour that this design supports that the current gdmsetup doesn't... guess we'd either need to fix gdm to support it, or do some cunning disabling.)
The Logo section allows the user to choose whether to show a logo or not, with thumbmail preview.
In both sections, the file chooser buttons should open a gtk file dialog with a thumbnail preview, so the user can visually confirm which file they're opening before they do so.
The Menubar section controls whether the Actions menu is shown in the login screen menubar, and whether or not it should contain the Configure Login Screen menu item, and/or the Hostname Chooser (XDMCP) menu item. (I'm not sure what the best name is for the XDMCP browser is-- it very likely isn't "XDMCP Browser", but we might want to retain some reference to XDMCP for those who know what it is.)
The Welcome Message and Allow system administrator to log in items are identical to those described under Themed, and should appear in the same location (i.e. they shouldn't jump around if you switch between Plain and Themed in the Style dropdown.)
The contents of the remote tab vary a little depending on what is selected on the Local tab. This is just one of gdm's (or is it X11's?) non-orthogonal features that makes this dialog so difficult to design :/ But here's my best attempt so far.
When the local login is set to Themed, there are four options for the Style dropdown on the Remote tab: Same as Local, Plain, Plain with Face Browser, or Remote Login Disabled.
Same as Local: the same controls are shown as for the Themed style on the Local tab, except that the Theme dropdown, theme list, Install and Remove buttons are disabled. This allows the user to see the theme details, but not to change them. I think this is slightly preferable to being able to edit them and have them change on both the Remote and Local tabs simultaneously, but I'm open to persuasion.
Plain / Plain with face browser: the same controls are shown as for the Plain and Plain with Face Browser styles on the Local tab, except that the menubar section is hidden, since the Actions menu can not be shown for remote logins AFAICT.
Remote login disabled: no controls are shown other than the Style dropdown.
When the local login is set to Plain or Plain with face browser, there are three options for the Style dropdown on the Remote tab: Same as Local, Themed, or Remote Login Disabled.
Same as Local: the same controls are shown as for the Plain or Plain with face browser style (whichever is selected) on the Local tab, except that all the corresponding Background and Logo controls are disabled. This allows the user to see the theme details, but not to change them. I think this is slightly preferable to being able to edit them and have them change on both the Remote and Local tabs simultaneously, but I'm open to persuasion.
There is one additional checkbox in the Background section that is not shown on the Local tab: Don't show image for remote logins. This is enabled only if the Image checkbox is checked, and, if checked, will prevent the image chosen on the Local tab from being shown for remote logins.
Themed: the same controls are shown as for the Themed style on the Local tab.
Remote login disabled: no controls are shown other than the Style dropdown.
This one's pretty straightforward in comparison :)
Enable accessible login turns on the accessibility features.
Allow users to change fonts and colors of plain greeter allows the user to change the gtk theme from the login screen, but again I was trying to use neither the term 'gtk', nor the term 'theme' which is used elsewhere in this dialog specifically to mean the gdm theme.
Login screen ready: if checked, a sound is played when the login screen is ready to accept input.
Login successful : if checked, a sound is played when a valid username and password combination are entered.
Login failed : if checked, a sound is played when an invalid username and password combination are entered.
For all three sounds, the sound is chosen with a standard GNOME file chooser button-- would be nice if the file dialog that opened included a Play button for previewing sounds before the file was chosen. There is also a Play button to the right of each file chooser button, to allow the user to preview the current sound.