Programming guideline of WinDom
Objects are caracterized by their type : the ob_type field of the
OBJECT structure. For example, the buttons have a G_BUTTON type. AES
includes some predefined type and it is possible to create a new
type. For that purpose, a special type is used : the G_USERDEF. This
type means that the aes call a special function when it has to draw
the object. A G_USERDEF object has an ob_spec pointing to a special
structure containing the address of the drawing object function. To
identifiate an object, AES uses only the low byte of the ob_type
field. So, the high byte value can be used by the user. In
particular, we use this field to give a second type to the userdef
objects. This value is called the extended type. All ressource
editors offer the possibility to edit this value.