This is a minimal SDL2 program that uses it's hardware accelerated renderer to allow ReShade to inject itself, thus serving as a very simple test program for programming shaders.
You'll find useful ReShade shaders in the res folder, like displaying a full screen texture, which you can copy to whatever folder you use to store ReShade's shaders.
The program should work with ReShade set in DirectX 9 mode, d3d9.dll, but you could try dxgi.dll or even opengl32.dll.
The program will create a generic config.ini if one doesn't exist, so you can tweak settings like initial width/height, vsync etc.
This program targets C++17, so build it with a compiler that's compatible with it.
You can press Alt+Enter to toggle fullscreen mode.