IMAGEOBJ: COPYFN vs COPYBUTTONEVENTINFN

[pamoroso]

What is the difference between the COPYFN and COPYBUTTONEVENTINFN functions of image objects?

[nbriggs]

Hmm... looking at the source, WINDOWOBJ, the IMAGEFNS methods are documented as:

(DATATYPE IMAGEFNS
    (DISPLAYFN     (* ; "FN called to display the object's image")
     IMAGEBOXFN               (* ; "To tell how big it is")
     PUTFN                          (* ; "To write it onto a file")
     GETFN                          (* ; "To read it back from the file")
     COPYFN                       (* ; "To make a copy of the object")
     BUTTONEVENTINFN  (* ;  "Called when the mouse goes down over the object")
     COPYBUTTONEVENTINFN    (* ;  "Called when the MIDDLE mouse button goes down over the object")
     WHENMOVEDFN                     (* ;  "Called when the object is moved within a document or other environment")
     WHENINSERTEDFN                (* ;  "Called when the object is inserted into a context")
     WHENDELETEDFN                 (* ;  "Called when the object is removed from a context")
     WHENCOPIEDFN                    (* ;  "Called when the object is copied within a context")
     WHENOPERATEDONFN         (* ;  "Called when something interesting happens to the object")
     PREPRINTFN
     IMAGECLASSNAME          (* ;  "LITATOM unique name by which this kind of IMAGEOBJ is to be known to the world.")
    )
  (SYSTEM))

I wonder why the PREPRINTFN didn't get an explanation.

[pamoroso]

The comment in the code seems to imply a programmatic copy for COPYFN but the IRM entry mentions "a copy-select operation", i.e. a user-initiated action.

[nbriggs]

I think the IRM entry is actually pretty clear. The COPYFN is for making a new instance of the object if/when the object gets copied to a new location - e.g., it might be making a deep copy of a bitmap rather than retaining a copy of a pointer to a bitmap (shared between the objects), while the COPYBUTTONEVENTINFN is involved in the user interaction. You can always break a function that you've put in your object and see how and when it gets called (and return different results to see the effects)