NAME
        MoveScreen -- Attempt to move the screen by the increments provided.

    SYNOPSIS
        MoveScreen( screen, deltax, deltay )
                    A0      D0      D1

        VOID MoveScreen( struct screen *, word, word );

    FUNCTION
        Moves the screen the specified increment, specified in screen
        pixel resolution coordinates.

        New for V36: screen movement limits have been greatly relaxed,
        to support screen scrolling.  In particular, negative values
        for screen LeftEdge and TopEdge may now be valid.

       If the DeltaX and DeltaY variables you specify would move the screen
       in a way that violates any restrictions, the screen will be moved
       as far as possible.  You may examine the LeftEdge and TopEdge fields
        of the screen structure after this function returns to see where
        the screen really ended up.

    INPUTS
        screen = pointer to a screen structure
        DeltaX = amount to move the screen on the x-axis
                Note that DeltaX no longer (V36) need be set to zero
        DeltaY = amount to move the screen on the y-axis
                Note that these coordinates are in the same resolution
                as the screen (such as HIRES or INTERLACE)

    RESULT
        None

    BUGS

    SEE ALSO
        screenposition(), rethinkdisplay()