https://bugs.winehq.org/show_bug.cgi?id=56755
--- Comment #7 from Ben Mayes czahrien@gmail.com --- I just attached a patch file and an archive containing a solution for a test application.
The test application needs to be built in Visual Studio. It loads a bitmap file, runs it through cascading conversions which cover the one added to converter.c, then renders it to the window.
The original bitmap is a 32 bit gradient with no noticeable color banding, due to the down conversion from 32 to 16 bit, color banding is visible on the displayed bitmap. Between this and the color accuracy, the conversion appears to be correct.
I am open to hearing any thoughts on how I could have potentially tested this entirely on Linux using the wine includes and libraries and winemaker rather than using Visual Studio. Although the examples online are rather straightforward a lot of them do not build because they utilize types and helper functions defined in d2d1helper.h which is not present in wine.