So to set the shape of a window i can use SDL_SetWindowShape, but how can I get the shape of a window once it has been set?
Probably there is no SDL_GetWindowShape because the surface you originally passed to SDL_SetWindowShape gets converted to whatever is the native representation of the shape (which could be a list of rectangles, for example), so for providing a SDL_GetWindowShape, code would need to be written to convert the native representation of each platform into an SDL_Surface.
It will be more efficient if you simply keep the surface you passed to SDL_SetWindowShape around, if you need it again later.
Ah ok, well i will do that then!