How to catch Gdk::BUTTON1_MOTION_MASK

[rockandsalt]

How do you catch the BUTTON1_MOTION_MASK? I'd like to get the location of my cursor on the widget when I press the middle mouse button. The goal is to implement a rotation feature in a opengl widget. The following code snippet are inside an Gtk::ApplicationWindow called mainWindow.

I tried :


glWidget.add_events(Gdk::BUTTON2_MOTION_MASK);
glWidget.signal_motion_notify_event().connect(sigc ::mem_fun(*this,&mainWindow::rotate));

with:

bool mainWindow::rotate(GdkEventMotion* motion_event)
{
cout<<"test"<<endl;
}

But the code doesn't react when I click the middle button.

The following snippet works when I replace the mask(BUTTON2_MOTION_MASK) with

Gdk:POINTER_MOTION_MASK

But it catches the signal and print test each time the pointer is on the widget which is not quite what I want.

[norobro]

I don't know enough about gtkmm to understand why one works but not the other.

Try putting your glWidget inside an EventBox and see if it works. https://developer.gnome.org/gtkmm-tutorial/3.0/sec-eventbox.html.en

[rockandsalt]

Hi thanks for the answer. In the end, I figured it out. I needed to add the Gdk::BUTTON1_MOTION_MASK and the Gdk::BUTTON_PRESS_MASK mask.


glWidget.add_events(Gdk::Button1_MOTION_MASK|Gdk:: BUTTON_PRESS_MASK);

But for some reason, this only react when I click the left mouse button. Still searching on how to get it to react to the middle mouse button.

[norobro]

If I understand what you are trying to do, the following seems to work:
mainWindow::mainWindow() {
set_default_size(600, 400);
m_eventBox.add(m_glArea);
m_eventBox.add_events(Gdk::BUTTON2_MOTION_MASK);
m_eventBox.signal_motion_notify_event().connect(si gc::mem_fun(*this, &mainWindow::rotate));
add(m_eventBox);
show_all_children();
}

bool mainWindow::rotate(GdkEventMotion* motion_event) {
std::cout<< motion_event->x << ", " << motion_event->y <<"\n";
return true;
}
Clicking the middle button on the mouse and dragging produces output like this:
173.118, 156.992
173.851, 158.459
173.851, 159.459
174.851, 160.459
175.851, 160.459
176.851, 161.459
...

[rockandsalt]

Hi thanks this works. I noticed that this will react to all the mouse button. This is not a problem since I can check which button was pressed using motion_event->state.
Since state is a bit mask, I went to the gdkModifier page (https://developer.gnome.org/gdk3/stable/gdk3-Windows.html#GdkModifierType) to find the correct constant to use if I want to check which key is pressed. But I noticed the value specified by GDK_BUTTON2_MOTION_MASK is different from what motion_event->state output.

For the middle button the state value is 529 while GDK_BUTTON2_MOTION_MASK is 512. I can probably check for the value 529 but this seems ghetto and will probably create problem if I port the program another platform. I checked with other button mask and they are all off aswell. Is that a bug or am I not using the correct constant?

I am currently running ubuntu.

[norobro]

You're welcome!

Is that a bug ...Dunno. For a 529 GDK_BUTTON2_MASK, GDK_MOD2_MASK and GDK_LOCK_MASK would be set. https://github.com/GNOME/gtk/blob/master/gdk/gdktypes.h#L234

Running the simple example above on my Debian box outputs 272, 528 and 1040 for mouse buttons 1-3.


One possible solution is, in your slot check to see if the bit for a button is set by doing a bitwise &. https://developer.gnome.org/gtkmm/stable/group__gdkmmEnums.html#ga0288c23e93ded8c0326235f1f 1120c61
Like so:
bool mainWindow::rotate(GdkEventMotion* motion_event) {
if(motion_event->state & GDK_BUTTON2_MASK) {
std::cout<< motion_event->x << ", " << motion_event->y <<"\n";
return true;
}
return false;
}