I tested with SDL2 (2.0.9 9bb50edccc46) on macOS 10.14 (18A391) and ported imgui_impl_opengl3.h, imgui_impl_opengl3.cpp, and main.cpp to C (checked calling to cimgui properly).

I faced with the problem of

Assertion failed: (g.IO.DisplaySize.x >= 0.0f && g.IO.DisplaySize.y >= 0.0f && "Invalid DisplaySize value"), function NewFrame, file imgui/imgui.cpp, line 3090.
Abort trap: 6

Download the project: cimgui-sdl2.tar.gz.

To build, simply ...

• make to build against gl3w
• make glew to build against glew

ps.

• notice that I have to do relative-path symlink cimgui.dylib as libcimgui.dylib, related to Symlink cimgui.dylib as libcimgui.dylib on macOS to pass linking phase #78 .
• X11 is installed at /opt/X11 and its include directory is added in Makefile as well.