MSMaskScrollMode [([]Mode.w[])] ; CookieMode/EraseMode/InvMode/SolidMode/MColourMode/MReMapMode/MSimpleReMapMode

The SMask family of Scroll commands can have a `type' of blit operation which is
set with this command. You can use the already existing Blitz functions or values
0, 1, 2 and 3 which represent CookieMode, EraseMode, InvMode and SolidMode. The
normal mode is CookieMode in which the source's stencil or cookie is used to
perform a blit in which areas of Colour 0 are transparent. EraseMode causes the
source's stencil or cookie to erase an area matching its shape on the
destination image. InvMode causes the destination to be inverted in the shape of
the source stencil or cookie, and SolidMode places a solid copy of the source's
stencil or cookie into the destination's image, which will appear as Colour 255.
MSMaskScrollMode also works with MColourMode, MReMapMode and MSimpleReMapMode. If
used as a function, MSMaskScrollMode will return a number representing the
current mode.