DN598161419

Subject: HELP WANTED: Tk and DND... long - DN [1]

Petasis George <petasis@iit.demokritos.gr> - 16 Mar 2000 - comp.lang.tcl

 Hi all,

 I am trying to write an extension that will offer
 an initial DND implementation to tk, under windows
 and unix. The current status is as follows:

 Currently, only text transfer is supported and the only action
 is copy (both of them have to change of course :-)).
 There is a running implementation for both platforms.
 The tcl side is exactly the same for both platforms. The types are
 given with their mime types. Under windows a modified version of
 the "olednd" extension is used. Under unix, the extension uses the
 XDND protocol. The protocol itself is implemented through the
 sample files given at the official protocol page (xdnd.c & xdnd.h).

 Under windows, everything work as expected. Some sporadic crashes
 of tk during exiting that the initial olednd package presented are
 corrected.

 Under unix (tested under linux RH6.1 & solaris 2.6), the dnd is
 working very well among different tk applications (or within the same
 application). The sample tests included with the "olednd" extension
 work exactly the same under both windows and unix.

 BUT (there is always a but :-)), there seem to be some problems in
 communications with other applications. As i don't have in my desktop
 applications that use that protocol (kde 1.x does not support it, v
 2.0 will support it and I have not installed gnome at all...),
 I downloaded and installed QT 2.1beta2 in my system. QT supports
 this protocol (up to version 4). I am using the "dragdrop" example
 program that comes with the distribution.

 The good news is that from a tk app you can drop an object in a qt
 application. But you cannot drop from qt to tk. When you try it,
 the feedback you get from the qt app (shown by the mouse cursor) is
 that all tk windows do not support dnd. The protocol defines that
 in order for a source application to see if the target window supports
 XDND is to see if it has the XdndAware window property.
 I am using the XChangePropery to add this property to any tk window
 that is a dnd source or target. And communication between tk apps is
 working. That means that the property is there, but QT for some reason
 fails to find it.

 After examing the toplevel qt windows with xprop, I found out that
 all of them have the property XdndAware defined, but they were not
 drop sources (they didn't have any drop types defined). I tried
 to reproduce this behaviour with tk, but i came to a problem:
 Seems, that I cannot add this property to toplevel windows.
 For example, if I make "." a drop target and then run xprop
 and select the "." window, this window does not have the XdndAware
 property. But dropping from another tk app works, and thats confusing
 me. Is there something I have missed? I mean tk toplevel windows are real
 toplevel windows? Why xprop cannot see the property, while another
 tk app does? The only explanation I can give is for tk toplevel windows
 to be inside another "special" window. Other tk apps can see the property,
 as the examing the window just under the cursor, but xprop doesn't,
 as it examines only the "parent" window. But according to the man
 pages this cannot be the case, because it is stated that tk toplevels
 are children of the root window. Does anyone has any idea what possibly
 goes wrong?

 The other thing I wanted to ask, is whether there is a simple way to
 add the ability to transfer images. If the user wants to drop an image
 and he gives me the name of a tk image as the data, is there an easy way
 to get the image data in a known format (i.e. gif)? Any sample code?

 Thanks,
 George