public DrawingManager(EscherDggRecord dgg) 
{
 // key = Short(drawingId), value=EscherDgRecord
        this.dgg = dgg;
}

 public int allocateShapeId(short drawingGroupId) 
{
        // Get the last shape id for this drawing group.
        EscherDgRecord dg = (EscherDgRecord) dgMap.get(new Short(drawingGroupId));
        int lastShapeId = dg.getLastMSOSPID();
        // Have we run out of shapes for this cluster?
        int newShapeId = 0;
        if (lastShapeId % 1024 == 1023)
        {
            // Yes:
                // Find the starting shape id of the next free cluster
            newShapeId = findFreeSPIDBlock();
                // Create a new cluster in the dgg record.
            dgg.addCluster(drawingGroupId, 1);
        }
        else
        {
            // No:
                // Find the cluster for this drawing group with free space.
            for (int i = 0; i <  dgg.getFileIdClusters().length; i++)
            {
                EscherDggRecord.FileIdCluster c = dgg.getFileIdClusters()[i];
                if (c.getDrawingGroupId() == drawingGroupId)
                {
                    if (c.getNumShapeIdsUsed() != 1024)
                    {
                        // Increment the number of shapes used for this cluster.
                        c.incrementShapeId();
                    }
                }
                // If the last shape id = -1 then we know to find a free block;
                if (dg.getLastMSOSPID() == -1)
                {
                    newShapeId = findFreeSPIDBlock();
                }
                else
                {
                    // The new shape id to be the last shapeid of this cluster + 1
                    newShapeId = dg.getLastMSOSPID() + 1;
                }
            }
        }
        // Increment the total number of shapes used in the dgg.
        dgg.setNumShapesSaved(dgg.getNumShapesSaved() + 1);
        // Is the new shape id  >= max shape id for dgg?
        if (newShapeId  >= dgg.getShapeIdMax())
        {
            // Yes:
                // Set the max shape id = new shape id + 1
            dgg.setShapeIdMax(newShapeId + 1);
        }
        // Set last shape id for this drawing group.
        dg.setLastMSOSPID(newShapeId);
        // Increased the number of shapes used for this drawing group.
        dg.incrementShapeCount();
        return newShapeId;
}

Allocates new shape id for the new drawing group id.

 public EscherDgRecord createDgRecord() 
{
        EscherDgRecord dg = new EscherDgRecord();
        dg.setRecordId( EscherDgRecord.RECORD_ID );
        short dgId = findNewDrawingGroupId();
        dg.setOptions( (short) ( dgId < <  4 ) );
        dg.setNumShapes( 0 );
        dg.setLastMSOSPID( -1 );
        dgg.addCluster( dgId, 0 );
        dgg.setDrawingsSaved( dgg.getDrawingsSaved() + 1 );
        dgMap.put( new Short( dgId ), dg );
        return dg;
}

 boolean drawingGroupExists(short dgId) 
{
        for ( int i = 0; i <  dgg.getFileIdClusters().length; i++ )
        {
            if ( dgg.getFileIdClusters()[i].getDrawingGroupId() == dgId )
                return true;
        }
        return false;
}

 int findFreeSPIDBlock() 
{
        int max = dgg.getShapeIdMax();
        int next = ( ( max / 1024 ) + 1 ) * 1024;
        return next;
}

 short findNewDrawingGroupId() 
{
        short dgId = 1;
        while ( drawingGroupExists( dgId ) )
            dgId++;
        return dgId;
}

 public EscherDggRecord getDgg() 
{
        return dgg;
}