How about a Modifier Key that, once down, temporarily disable the link mode? (icon would be updated to give a visual feedback)
Once the key released, the link mode is back on.

Can be done by reimplementing:
virtual void QWidget::keyPressEvent(QKeyEvent event);
and
virtual void QWidget keyReleaseEvent(QKeyEvent event);

See test branch here: https://github.com/fedorov/Slicer/branches/link-modifier

---------- Forwarded message ----------
From: Julien Finet <julien.finet@kitware.com>
Date: Sun, Jan 29, 2012 at 10:30 PM
Subject: Re: qLineEdit in a ctkPopupWidget
To: Jim Miller <millerjv@gmail.com>
Cc: Jean-Christophe Fillion-Robin <jchris.fillionr@kitware.com>

Hi Jim,
It seems that it's not possible. I spent some try to debug and my observations are:

• to get focus on click, QLineEdit must be in a window that is active. For some reasons, ctkPopupWidget is not a window but it belongs to the window of the base widget. I changed the code to make it an active window, but a 2nd problem appears.
• once the ctkPopupWidget is an activeWindow, QLineEdit still doesn't receive key events, only the base widget receives them. I've no idea why, but it might be because ctkPopupWidget is considered as a Qt::ToolTip type and not a regular type. :-/

The only work around I found is to make the QLineEdit into a popup inside the popup.
ctkPopupWidget popupWidget(baseWidget);
...
layout->addWidget(&button);
popup.setLayout(layout);

QMenu menu = new QMenu;
QWidgetAction lineEditAction = new QWidgetAction(menu);
lineEditAction->setDefaultWidget(new QLineEdit);
menu->addAction(lineEditAction);
button.setMenu(menu);

But then I face some always-on-top issues. I'm not sure there is an easy fix :-/ I wonder, maybe ctkPopupWidget should be a Qt::Popup (or Qt::Tool) instead of a Qt::ToolTip...

Julien.

On Sun, Jan 29, 2012 at 5:03 PM, Jim Miller <millerjv@gmail.com> wrote:
Julien, JC,

I am trying to use a qLineEdit widget inside a ctkPopupWidget. I can set the text for the QLineEdit fine. I can pull up the context menu and paste text into the QLineEdit fine. But I cannot type any text. It is like the LineEdit never gets the focus. I click in the entry area but not cursor appears. It looks like the widget is enabled.

Is there something special in the ctkPopupWidget that would prevent widgets like the LineEdit widget?

Looking at the code, there appears to be code managing "something" on mouse over.

Jim

Per discussion with JC, J2, Tobias and Andrey, it was agreed:

• to add a method SliceLinkLogic::SetLinkScopeModifier(LinkPropertiesModifier)
• LinkPropertiesModifier will be defined as a bitset that would allow turning off individual linking modes (eg, Bg, Fg, Label)
• the modifier will be set in the python startup script
• the option to add an application setting, visual feedback for the user (changing color of the volume selector or icon) will be considered later

Suggested patch is available here: https://github.com/fedorov/Slicer/tree/1772-linking-modifier

Currently waiting for Jim to approve/comment.

If resolving that issue before Sept 1st does not sound reasonable, please let me know. Thanks Jc

Link modifier API added in r20856 and r20857