Internal data structures

• int cmdCode - the unique integer ID of the command; this is one of the names in the main enumeration described above.
• int cmdSize - the number of bytes which the data will occupy when copied into a given display list.
• void *Data - a block of cmdSize bytes which stores the data to be copied into a given display list.
• void *dataLoc - a pointer to the last place into which the bytes in Data were copied. If it is NULL, the data has not yet been copied. This is stored so that the reput command can copy new data over previously-stored data, instead of just appending the data to the end of a display list.