When rendering to a texture map and then putting that texture map onto a quad. The texture is swapped between opengl and directx. I've attached an example program. 

The result with env QSG_RHI_BACKEND=opengl

The result with env QSG_RHI_BACKEND=directx

If you look at the textures in NVidia's NSight. You'll notice that DirectX use top left as 0,0 for the origin in a texture and in OpenGL, it's the bottom right. 

DirectX:

OpenGL: