Megadrive bitmap rotator

• 13 November 2026
• notes,
• megadrive,
• gamedev,
• doohicky,
• demo

Pretend this image is spinning

It turns out the Megadrive can rotate a large graphic at 60FPS without helper hardware!

All code and graphics assets ME except the underlying SGDK bits which i'm using as a foundation, Hi Stef!
Uses my M68K Assembler tool judiciously to create the rotation kernels.

Controls

A = Change background mode  
    0   :   NOTHING  
    1   :   Tilemap demo  
    2   :   Moon VRAM state  
B = Set Software render on/off  
    Will smoothly scroll then snap back  
C = Set Hardware shifters on/off  
    Will turn in large increments when it feels like it  
ARROWS =  
    SCROLL BACKGROUND (mode 1)  

FILE

HERE ---> Download (128KB Sega Megadrive/Genesis ROM) <--- HERE

Tested in Blastem emulator, Clownmdemu emulator, and on a PAL Model2 Megadrive.