I believe it's this from workbench/workbench.h include file:
struct DrawerData {
struct NewWindow dd_NewWindow; /* args to open window */
LONG dd_CurrentX; /* current x coordinate of origin */
LONG dd_CurrentY; /* current y coordinate of origin */
};
struct DiskObject {
UWORD do_Magic; /* a magic number at the start of the file */
UWORD do_Version; /* a version number, so we can change it */
struct Gadget do_Gadget; /* a copy of in core gadget */
UBYTE do_Type;
char * do_DefaultTool;
char ** do_ToolTypes;
LONG do_CurrentX;
LONG do_CurrentY;
struct DrawerData * do_DrawerData;
char * do_ToolWindow; /* only applies to tools */
LONG do_StackSize; /* only applies to tools */
};
Get the SDK for all the details you might need.
