Do I just draw, make a texture and use blending and alpha?
Drawing a ‘translucent filled rectangle’ can be achieved as follows. where alpha
is set to the desired opacity:
SDL_SetRenderDrawBlendMode(renderer, SDL_BLENDMODE_BLEND);
SDL_SetRenderDrawColor(renderer, r, g, b, alpha);
SDL_RenderFillRect(renderer, &rect);
Yay, that worked, thanks rtrussell.