[Bug 173833] thumbnail.png adds solid white padding to force a square aspect ratio instead of preserving page dimensions or using transparency

[bugzilla-daemon]

https://bugs.documentfoundation.org/show_bug.cgi?id=173833

--- Comment #2 from Ismail <lh.ismagh...@gmail.com> ---
(In reply to V Stuart Foote from comment #1)
> Don't think that is true. The thumbnail view in recentdocsviewitem() as used
> for the MRU history recorded to profile, and showining in the StartCenter,
> and also for saving into ODF archive as preview (that os/DE file managers or
> LO's own file manager can parse) does take a default ratio into account.
> 
> And, believe we now can have thumbnail previews that use transparency, so
> may need some rework for the getModuleOverlay(). 
> 
> But the flow for these preview images gets over my head pretty quick.
> 
> @Justin, is that correct understanding?


I double-checked the saved ODF container and confirmed:

Inside .odt Archive: The Thumbnails/thumbnail.png file is indeed saved as a
clean rectangular image, preserving the page's original aspect ratio.

StartCenter: Displays the thumbnail correctly as rectangular.

Windows File Explorer: However, in Windows File Explorer, the preview is
displayed with solid white padding on the sides to force a square shape.

Since the core thumbnail generator creates a proper rectangular PNG, I suspect
this might be related to how the preview is handed over to Windows File
Explorer—perhaps somewhere in the Windows Shell Extension (shlxthdl) or the
thumbnail provider handler? It seems possible that the bitmap is being rendered
onto a square canvas with a solid white background before being delivered to
the OS, rather than keeping the background transparent or preserving the native
aspect ratio.

I'm not entirely sure about the exact technical pipeline here, but hopefully
this observation helps narrow down where the white padding is being added!

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