While testing the speed of SDL_RenderDrawLinesF on different renderers I noticed a big difference when passing -1 (to SDL_CreateRenderer to let it choose the best renderer) compared to specifying an other renderer. Usually -1 chooses rendering index 0, but even specifying 0 directly causes SDL_RenderDrawLinesF to run slower. So what gives? What’s special about -1? Why should it be any different to manually choosing the renderer it will choose.
Renderer 0 on my PC is direct3d, 1 is direct3d11 which is much slower for line drawing.