How will flipping pictures cause the game to take less disk space? Just wondering, as by flipping sprites inside the game, the file the sprite is made from still exists in the game, and will in no way change its size.
Oh, and the only solution to actually flipping (mirroring a picture), you would have to do this using the bitmap of the picture. 'self.bitmap' does work within the Sprite_Picture class, so inside Spriteset_Map you can use the code:
@picture_sprites[number].mirror
Replace number with whatever the picture number is.
I hope this helps. If this was not what you meant, try to be more descriptive next time.
Cheers.