Mostly C port of Microsoft's Simple Direct2D tutorial
This is a largely-C port of the Direct2D tutorial that can be found at https://docs.microsoft.com/en-us/windows/win32/direct2d/direct2d-quickstart, where all the code are converted to plain C89 C, except for the part where we use ID2D1HwndRenderTarget::GetSize, as there are issues in the C interface of this code that we must call this using C++.
This is tested on Visual Studio 2008 Win32/x64 configs, and should work on later versions of Visual Studio, up to and including 2019.
You will need a d2d1.h header that contains C definitions of methods for this to work, so for Visual Studio 2015 and later you will need to first target the Windows 10 SDK 10586 or earlier, using [vcvars|vcvarsx64].bat 10.0.10586.0, as the later Direct2D headers removed the C definitions of the Direct2D COM functions.
Compile in a Visual Studio command prompt as follows (for release builds): cl /MD /O2 /W3 /GL /Zi d2d-sample.c d2d-sample-helper.cpp /link /DEBUG /opt:ref /LTCG d2d1.lib ole32.lib user32.lib
(for debug builds): cl /MDd /Od /W3 /GL /Zi d2d-sample.c d2d-sample-helper.cpp /link /DEBUG d2d1.lib ole32.lib user32.lib