MSBlockScroll X1.w,Y1.w,Width.w,Height.w,X2.w,Y2.w[,SourceBitmapNum.w] ; Block-Copy bm 2 bm and st 2 st

Stencil-BlockScrolls an area within the currently used chunky Bitmap, or using a
different source Bitmap if specified. Width, X1 and X2 should be multiples of 16.
If SScrollCut is Off, a normal `SBlockBlit' will be performed in which the source
Bitmap's graphic will be mask-blockcopied to the destination Bitmap's graphic
(with masking), and the source Bitmap's stencil is copied to the destination
Bitmap's stencil (with masking). If SSCrollCut is On, the destination Bitmap's
stencil willbe used to protect areas of the destination Bitmap's graphic, instead
of copying the source stencil into the destination stencil, effectively scrolling
the source image `behind' the protected parts of the destination. Both source and
destination Bitmaps should have stencils. 040+ routines are used where possible
but not when MSScrollCut is On as this is not possible.