Option to Flip ES Screen Output (to work in a mirror) on a CRT TV (Pi2Scart)

[oneswitch]

RetroPie shaders can flip screen output vertically (and horizontally and rotate 90, 180, 270 degrees) - (see this forum post). This means a game can be played in a reflected mirror / reflective surface horizontally or vertically.

My personal wish for this is to get a Pi2Scart RetroPie vertical CRT set-up in my Space Invaders Taito machine, that uses a mirror to reflect and merge the screen onto a cardboard moonscape. My question is...

...could anyone here make EmulationStation work in this way using Pi2Scart? It can be done with HDMI from the boot file, but I've not found a way to do it using Pi2Scart or composite video output.

[Sakitoshi]

display_rotate works for composite out.

display_rotate=0 Normal
display_rotate=1 90 degrees
display_rotate=2 180 degrees
display_rotate=3 270 degrees
display_rotate=0x10000 horizontal flip
display_rotate=0x20000 vertical flip