ifIf you use the SDL2 Renderer you should, say goodbye to the idea of accessing the pixelpixels directly. ofOf course this is, it is possible but everytime you do this you "download" the pixel everytime from your graphiccardgraphics card and then you have to push themit up again.
I would suggest you, that you do all pixel manipulation beforebefore in a SDL_SurfaceSDL_Surface and you load the result as texture into you graphicgraphics card OR use OpenGL complete.