When allocating using a friend bitmap, it is not safe to assume
anything about the structure of the bitmap data if that friend
BitMap might not be a standard amiga bitmap (for instance, if the
workbench is running on a non-amiga display device, its
Screen->RastPort->BitMap won't be in standard amiga format. The
only safe operations to perform on a non-standard BitMap are:
- blitting it to another bitmap, which must be either a
standard Amiga bitmap, or a friend of this bitmap.
- blitting from this bitmap to a friend bitmap or to a
standard Amiga bitmap.
- attaching it to a rastport and making rendering calls.
Good arguments to pass for the friend_bitmap are your window's
RPort->BitMap, and your screen's RastPort->BitMap. Do NOT pass
&(screenptr->BitMap)!
BitMaps not allocated with BMF_DISPLAYABLE may not be used as
Intuition Custom BitMaps or as RasInfo->BitMaps. They may be
blitted to a BMF_DISPLAYABLE BitMap, using one of the BltBitMap()
family of functions.