Hello,

i have my own image format (for medical system). I want to display thumbnails in Windows Explorer. I am on W7 x64 and try to port a DLL that worked on XP..
I developp my DLL that exports a IThumbnailProvider::GetThumbnail, and returns a HBITMAP.
It works quite well and the DLL is well called for cx = 1024, cx = 256, cx = 480 and cx = 96 by the system, and thumbnails are displayed in all parts of explorer.... -in all sizes of icon..
(I save also bmp in a debug directory to be sure bitmap are well generated by DLL + a log file and it's ok).

However, they sometimes appear totally black, and in this case, DLL in not called again (image is taken into cache?). For example, if I leave the directory, and then come back again, all well displayed thumbnails are black...

What does Windows makes with the bitmap handle I give it?
Is that a configuration of Windows? Which one?
Did I missed something in code? (I follow msdn help to write it).

Thanks for any help, I'm out of idea, and already spent two days on forums..

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