I think I know how uxtheme works...

Jonathan Wilson jonwil at tpgi.com.au
Wed Mar 23 20:19:23 CST 2005

What I strongly suspect happens is this:
1.The themes service is always loaded and running and holds the theme data 
(and it contains details of which .msstyles file to use)
2.At some point (either at startup if the changes are global or when an app 
loads if the changes are app specific, I cant find where this bit happens 
but I suspect the themes service does this) control passes to ordinal 34 in 
uxtheme.dll (aka ThemeHooksInstall acording to uxtheme.pdb). This function 
calls an undocumented function in user32 called RegisterUserApiHooks (which 
appears to be taylor made for uxtheme to do what it needs to do).
The function hooks:
PreWndProc (probobly stuff that happens internally before the window 
procedure gets called)
PostWndProc (probobly stuff that happens internally after the window 
procedure gets called)
PreDefDlgProc (probobly connected to dialog boxes)
PostDefDlgProc (probobly connected to dialog boxes)
MDIRedrawFrame (probobly related to MDI frame windows)
This is what causes all apps (including non-theme-aware ones) to get themed 
non-client areas (window borders etc)
3.Apps that are theme aware have a manifest, load comctl32.dll 6.0 and 
probobly have to call InitCommonControlsEx (although I think some of the 
code in the dllmain for comctl32.dll 6.0 may also end up calling 
InitCommonControlsEx). This causes new versions of the stock classes 
(button, list box, edit, combo box etc etc etc) to be created and 
registered. A cursory examination of some of these classes shows that they 
dont seem to "pull code" from the stock implementation in user32.dll (i.e. 
anything they dont themselves handle goes back to DefWindowProc). In 
particular, it doesnt appear as though they have any knowledge of the 
classes or window procedures contained in user32.dll.
then 4.Apps that need to do something extra call into functions exported by 
uxtheme.dll to do whatever they need to do.

user32.dll seems to have no knowledge whatsoever about themeing and 
uxtheme. All that user32 has is RegisterUserApiHooks (and the matching 
UnregisterUserApiHooks) that uxtheme uses to hook into user32.dll and do stuff.

Exactly how the theme service and theme engine works "under the hood" 
doesnt matter.
But for ReactOS and WINE purposes, I suggest we implement the following:
1.A function similar to RegisterUserApiHooks/UnregisterUserApiHooks (either 
reverse engineer the MS function or write our own). This will allow uxtheme 
to hook into the global drawing for things like window borders without 
user32 needing to care about uxtheme and what uxtheme does (just like how 
MS hooks into user32 that way)
2.Whatver code is necessary to get the hooks installed right so that all 
apps get the "global" theming like on real windows
3.Support to read the manifest and load a new comctl32.dll that would be 
like the version 6 from microsoft (and would contain complete theme-aware 
implementations of the stock controls just like MS comctl32.dll 6.0 does)
and 4.All the needed uxtheme exports to make stuff run

This would be the same way Microsoft does things.
User32.dll would have no idea whatsoever about uxtheme and theming
All apps would get non-client-area themeing like on windows.
And only theme aware apps would get themed controls etc (the rest would get 
"stock" windows controls)

Oh and btw, if this "reverse engineering" is not "clean room" enough for 
WINE and ReactOS, let me know and I will stop posting it :)

More information about the wine-devel mailing list