MSBlit [ShapeNumber.w,]Xpos.w,Ypos,w ; Blit shape to bitmap and cookie to stencil, any coords

Performs a straight masked-blit of a chunky Shape into a chunky Bitmap to
coordinates Xpos,Ypos. If the ShapeNumber is omitted the currently used Shape is
used. The type of blit performed is defined with the MSBlitMode command. Normally
the Shape is simply cookie-blitted onto the Bitmap, with areas of Colour 0 as
transparent. If SBlitCut is Off, the same operation is performed with the Shape's
cookie, in which the cookie is blitted to the Bitmap's stencil using the same
SBlitMode. If SBlitCut is On, the Bitmap's stencil will act to protect areas of
the Bitmap's image, causing the Shape to be blitted `behind' the protected areas.
With SBlitCut On the cookie is no longer copied to the stencil.