tokumaru wrote:
Hacking an existing game is more complex, because you can't easily tell if you have enough time to do the extra stuff you want. The game may very well have been "tuned" to use all of the vblank time (which is the only time you're allowed to write to VRAM if rendering is on) under certain conditions, and if you try to put the extra 140 to 200 cycles that updating 16 bytes takes, you might extrapolate the allowed time for updates an end up with corrupted graphics/scroll, even though the copy procedure by itself is correct.
To hack a game you need more than just the knowledge of how to perform a certain task, you need to know how that task and the time it takes will affect the existing game engine, in order to avoid any conflicts and timing issues.
Thanks I read about VBlank. I'm pretty sure I know some function which will check that and I will be able to use this
I'm glad you mentionned it I forgot about this.