Very nice!

Scrolling performance is perfect, don't remove the transparency. How much of the image are you rotating? Rotating the entire image is probably faster than changing line orientation and rotating each text separately, even though there would be fewer pixels being rotated. Maybe you could determine the area that shifts and blit its already rotated form. Then draw the newly exposed area and only rotate the new area onto the screen. Unless that is already what you do.

I know this just a test and the final will change a lot but the rotation icon should open a menu with As to quickly select an orientation.

Can't wait for it to be finished.