The Blitting Processor is a component of the Wii's GX subsystem. It is responsible for copying the EFB to the XFB, doing the RGBA->YCbCr conversion and scaling/antialiasing in the process.
BP (blitting processor) registers
The BP registers are accessed by writing a 8-bit value of 0x61 to the FIFO, followed by 32 bit value. This value is a bit weird - the high 8 bits are the register, and the low 24 bits are the register value.
EFB source registers
One can specify which part of the EFB is copied to the XFB or texture, using the following BP registers:
- 0x49: coordinates to top left of rectangle in EFB that will be copied (packed format, unknown)
- 0x4a: width and height-1 of rectangle to copy in EFB (again, unknown packed format)
XFB destination registers
The destination of the copy in the XFB is specified by the physical address of the XFB and the row stride (basically width of row, but no scaling appled).
- 0x4b: Address of destination (XFB). BEWARE: You only have 24 bits, which means your XFB must reside somewhere in the low 16MiB of RAM.
- 0x4d: Low 10 bits specify row stride of destination.
Copy control register
|Field||Begin copy||Clear enable|
- 0x52: This register starts a copy. Important bits:
* bit 10: Clear enable flag * bits 12-15: Set all to 1 to enable a copy.
Copy filter registers
Registers 0x01-0x04 are used for tricks like antialiasing. For a plain copy (i.e. no antialiasing) set all for to 0x666666.
Beginning a copy
The following must take place to do a copy:
- Setup clear and z clear registers (optional)
- Set source and destination registers
- Write to display copy control register to begin a copy
- Set clear, z, and control registers again (what? doubt necessary, libogc GX is stupid)