What component is responsible for tray and how to manipulate it using C++?

Question

My goal is to write a desktop gui application that will utilize these commands found in https://askubuntu.com/a/14083/18330

pacmd list-sinks to list name or index number of possible sinks

pacmd set-default-sink "SINKNAME" to set the default output sink

pacmd set-default-source "SOURCENAME" to set the default input

pacmd set-sink-volume index volume

pacmd set-source-volume index volume for volume control (0 = Mute, 65536 = 100%)

Then the application will have a tray icon that shows a list of sound devices that will be clickable to switch the sound device to that one. As they are clicked the sound volume will fade volume from 0 to the point the current system's volume (therefore I need access to the system volume as well.)

Unknowns:

How to programmatically add a tray icon in c++
How to make a drop down display when clicked on that tray icon and have it display items that are also clickable (much like how the mail icon displays Thunderbird)
How to bind the click events to a c++ function that will run (in order to switch to that sound device I will have a c++ function ready.)

I just need some guidance about identifying the desktop component that I'm trying to manipulate and where to find the API documentation for it.

Notes:

Using Ubuntu 14.04 LTS amd64
Going to write this as an open source Node.js extension written in C++
This is an example of notifications written as a Node.js C++ extension

Thank you this was the information I was looking for. Please write an answer with examples to collect the bounty. — Logan, Oct 25 '14 at 00:28
@Logan, for its doc's see: https://askubuntu.com/questions/42211/how-to-create-unity-indicators/234204#234204 — user.dz, Oct 25 '14 at 10:25

score 1 · Answer 1 · edited Apr 13 '17 at 12:25

Check out libappindicator. It is responsible for putting the icon in the tray. The dropdown menu displayed by the indicator is a GtkMenu. The rest should be familiar if you worked with GTK+. Here is a minimal example.

#include <gtk/gtk.h>
#include <libappindicator/app-indicator.h>

static void do_something(GtkWidget *widget, gpointer data) {
  //...
}

int main (int argc, char **argv) {
  gtk_init(&argc, &argv);
  GtkWidget *menu = gtk_menu_new();
  GtkWidget *menuitem = gtk_menu_item_new_with_mnemonic("_This is a menu item");
  gtk_menu_shell_append(GTK_MENU_SHELL(menu), menuitem);
  g_signal_connect(menuitem, "activate", G_CALLBACK(do_something), NULL);

  /* the second parameter is the icon displayed */
  AppIndicator* ind = app_indicator_new("test", "indicator-messages-new", 
                     APP_INDICATOR_CATEGORY_APPLICATION_STATUS);
  app_indicator_set_menu(ind, GTK_MENU(menu));
  gtk_main();
}

You compile it with the following. You'll need libgtk2.0-dev and libappindicator-dev packages.

$ gcc test.c `pkg-config --cflags --libs gtk+-2.0 appindicator-0.1`

You'll figure out the rest. The easiest way is to check out other simple indicator applications. For example, see the indicator from this answer.

What component is responsible for tray and how to manipulate it using C++?

1 Answers1