moduleH-Blank direct memory access
It allows to change how things are drawn in each screen horizontal line, since they transfer data to the GBA during each horizontal blanking (H-Blank) period.
For example, with HDMA you can change the transparent color every screen horizontal line, which is how games like Chrono Trigger fills their menus with a color gradient.
It differs from H-Blank effects in that multiple registers can be written by HDMA in each screen horizontal line, but since there's only one DMA channel available, written registers must be consecutive.
It is also lower level than H-Blank effects, so you should try with H-Blank effects first.
- file bn_hdma.h