[Mono-winforms-list] libgdiplus 32-bit BMP support

[Kornél Pál]

Hi,

I am working ImageListStreamer. Win32 image lists support 32-bit bitmaps and
comctl32.dll version 6.0 has 32-bit ARGB alpha channel support.

MS GDI+ can load 32-bit bitmaps, it loads the if they were 32-bit RGB, uses
no alpha channel, but alpha channel is preserved in memory. This means that
nither GetPixel nor Graphics use alpha channel but alpha channel can be
obtained using LockBits.

libgdiplus seems to use Format32bppArgb instead of Format32bppRgb for 32-bit
BMPs that is bug:
http://bugzilla.ximian.com/show_bug.cgi?id=76562

Is it safe to assume that libgdiplus will preserve alpha channel for
LockBits even if it will use Format32bppRgb for 32-bit BMPs?

Kornél