Defining Your Own Control Definition Function
A control definition function determines how a control generally looks and behaves. Various Control Manager functions call a control definition function whenever they need to perform a control-dependent action, such as drawing the control on the screen. In addition to standard control definition functions, defined by the system, you can make your own custom control definition functions.The Control Manager calls the Resource Manager to access a control definition function with the given resource ID; for a description of how to derive a control definition function ID, see "Control Definition IDs". The Resource Manager reads a control definition function into memory and returns a handle to it. The Control Manager stores this handle in the
contrlDefProcfield of the control structure.When various Control Manager functions need to perform a type-dependent action on the control, they call the control definition function and pass it the variation code for its type as a parameter. You can define your own variation codes; this allows you to use one
'CDEF'resource to handle several variations of the same general control. See "The Control Definition Function Resource" and "The Control Resource" for further discussion of controls, their resources, and their IDs.If you choose to provide your own control definition functions, these functions should apply the user's desktop color choices the same way the standard control definition functions do. You can use control color tables of any desired size and define their contents in any way you wish, except that part indices and messages 0 through 127 are reserved for system definition.