HowTo.txt

1, How to build

The easier way would be to build the project with Admin access rights (run VS as Admin), or
follow step 2 after building dll.

2, How to setup/install the handlers for Windows

To register, run (as admin):
	regsvr32 EMFExplorerHandlers.dll

To unregister, run (as admin):
	regsvr32 /u EMFExplorerHandlers.dll

3, How to debug

Use PreviewHandlers
https://www.brad-smith.info/blog/archives/183

Or:

See MSDN example here

C++ Windows Shell thumbnail handler (CppShellExtThumbnailHandler)
https://code.msdn.microsoft.com/windowsapps/CppShellExtThumbnailHandler-32399b35

===== QUOTE BEGIN =====
Debugging thumbnail handlers is difficult for several reasons.

1) The Windows Explorer hosts thumbnail providers in an isolated process to 
get robustness and improve security. Because of this it is difficult to debug 
your handler as you cannot set breakpoints on your code in the explorer.exe 
process as it is not loaded there. The isolated process is DllHost.exe and 
this is used for other purposes so finding the right instance of this process 
is difficult. 

2) Once a thumbnail is computed for a particular file it is cached and your 
handler won't be called again for that item unless you invalidate the cache 
by updating the modification date of the file. Note that this cache works 
even if the files are renamed or moved.

Given all of these issues the easiest way to debug your code in a test 
application then once you have proven it works there test it in the context 
of the explorer. 

Another thing to do is to disable the process isolation feature of explorer. 
You can do this by putting the following named value on the CLSID of your 
handler

   HKCR\CLSID\{CLSID of Your Handler}
       DisableProcessIsolation=REG_DWORD:1

Be sure to not ship your handler with this on as customers require the 
security and robustness benefits of the isolated process feature.
===== QUOTE END =====

So, to debug a shell handler, you need to first make sure it's registered
in the system first. 

Then, edit the registry as mentioned above, or run the reg file
	DisableHandlerProcessIsolation.reg
	(to restore, run EnableHandlerProcessIsolation.reg)

To debug the *thumbnail* handler dll, you need to attach the debugger to:
	explorer.exe
	
To debug the *preview* handler dll, you need to attach the debugger to:
	prevhost.exe
	
Note: if that didn't work, you might need to try one of these (or all of them):
a, Terminate the host process accordingly.
b, Figure out a way to update the modify date of the sample file (*.opju,*.ogg),
such as edit the file with VS in hex mode, normally simply change a random byte
would do the trick (just remember to restore it back).