How to convert GDI bitmap to QPixmap

[Cesar]

How to convert a GDI GpBitmap* to QPixmap?

[Chris Kawa]

There's no direct conversion, but QImage can be created from HBITMAP, so you can do it in 2 steps: create HBITMAP from GpBitmap and then create QImage out of that. Something like:

Gdiplus::GpBitmap* gpBitmap = /* something */;
HBITMAP bitmap {};
Gdiplus::DllExports::GdipCreateHBITMAPFromBitmap(gpBitmap, &bitmap, Gdiplus::Color::Transparent);
QImage image = QImage::fromHBITMAP(bitmap);
DeleteObject(bitmap);

Note that QImage::fromHBITMAP is available in Qt6.
In Qt5 it was part of a separate module QtWinExtras: QtWin::imageFromHBITMAP()

It's a bit of a waste because it's doing two conversions. If you care for performance the best would be to get access to the GpBitmap raw data and create QImage from that directly, but that's more work. The above is the lazy way.

[Cesar]

Does it preserve transparency?

get access to the GpBitmap raw data and create QImage from that directly

Do you mean lockbits?

[Chris Kawa]

Does it preserve transparency?

I don't know. Check.

Do you mean lockbits?

Yeah, probably, although from what I understand it also does a copy and conversion to the format you specify, so maybe it's not worth it.,