Re: GSDragView wrong position

[Richard Frith-Macdonald]

On 2005-04-01 13:24:33 +0100 Enrico Sersale <enrico@dtedu.net> wrote:

> On 2005-04-01 12:19:37 +0300 Richard Frith-Macdonald 
> <richard@brainstorm.co.uk> wrote:

> > location. Looking at it on my system, the visible icon image actually 
> > appears a few pixels above and to the right of the the mouse pointer ... 
> > if 
> > the image has a transparent border it could explain that small offset, if 
> > not ... I guess there is a bug there.  Is that the problem you are 
> > referring 
> > to?
>
> In this case you are right. All the GWorkspace icons use -locationInWindow: 
> and -convertPoint:fromView: before starting the drag.

I believe that's what they should be doing if they want the bottom left 
corner of the image to appear at the mouse location specified in the event 
triggering the drag operation.

 Now I should only add
> the offset calculation.

I think this is only needed where the mouse has already been dragged and you 
are passing the image coordinates relative to the mouse-down event.  If I 
understand it correctly, the offset is supposed to be used to adjust the 
position of the image to where it would have been if the image drag had 
started immediately on mouse down.

> Other classes as NSColorPanel, NSImageView, NSToolbarItem, etc. use 
> NSZeroPoint as argument. In these cases the position is shifted up and 
> right. 
> This should be fixed.

I've changed NSColorPanel and NSImageView to center the image on the mouse 
position ... I hope that's the desired/correct behavior.

> But my doubt comes from NSTableView.
> In -mouseDown:, NSTableView should calculate the position of the image 
> using 
> its -dragImageForRows:event:dragImageOffset: method; the third argument of 
> this method is a pointer to a NSPoint that must be used after in 
> dragImage:::::::. The standard implementation returns an 8x8 empty NSImage 
> and ignores the NSPoint pointer (and -mouseDown: uses NSZeroPoint for the 
> position and NSZeroSize for the offset).
>
> Now, we have two classes that inherit from NSTableView: FSNListView in GW 
> and 
> ExtendedOutlineView in GNUMail; both these classes override 
> -dragImageForRows:event:dragImageOffset: to return the right drag image; 
> but 
> both the classes ignore, as NSTableView does, the NSPoint.
>
> The strange think is that, with this code, GNUMail runs perfectly on OS X...

Reading the documentation for -dragImageForRows:event:dragImageOffset: I saw 
that the image was supposed to be centered on the mouse pointer but adjusted 
by the offset returtned fropm that method.  The code was not doing that at 
all, so I implemented that behavior as far as I understand it.

The thing I lack is tests/examples.  Please could you give me some 
instructions as to how I can reproduce problems using GWorkspace and 
GNUMail.  I've never done much with DnD in either one, and don't know what 
the expected/correct behavior is.  I don't have any GNUstep apps running on 
MacOS-X/Cocoa for comparison either :-(