NAME   

     InitBitMap -- Initialize bit map structure with input values.

   SYNOPSIS
        InitBitMap( bm, depth, width, height )
                    a0   d0     d1      d2

        void InitBitMap( struct bitmap *, byte, uword, uword );

   FUNCTION
        Initialize various elements in the bitmap structure to
        correctly reflect depth, width, and height.
        Must be used before use of bitmap in other graphics calls.
        The Planes[8] are not initialized and need to be set up
        by the caller.  The Planes table was put at the end of the
        structure so that it may be truncated to conserve space,
        as well as extended. All routines that use bitmap should
        only depend on existence of depth number of bitplanes.
        The Flagsh and pad fields are reserved for future use and
        should not be used by application programs.

   INPUTS
        bm - pointer to a bitmap structure (gfx.h)
        depth - number of bitplanes that this bitmap will have
        width - number of bits (columns) wide for this bitmap
        height- number of bits (rows) tall for this bitmap

   BUGS

   SEE ALSO
        graphics/gfx.h