Added a mockup of the Source Capabilities dialog

It's not functional yet, but it opens when the Source Capabilities list
item is clicked on the Sink page.  It looks about right, so that's a
start!

data/src-cap-dialog.ui

+<?xml version="1.0" encoding="UTF-8"?>
+<!-- Generated with glade 3.20.0 -->
+<interface>
+  <requires lib="gtk+" version="3.20"/>
+  <object class="GtkDialog" id="src-cap-dialog">
+    <property name="can_focus">False</property>
+    <property name="title" translatable="yes">Source Capabilities</property>
+    <property name="modal">True</property>
+    <property name="type_hint">dialog</property>
+    <child internal-child="vbox">
+      <object class="GtkBox">
+        <property name="can_focus">False</property>
+        <property name="orientation">vertical</property>
+        <child internal-child="action_area">
+          <object class="GtkButtonBox">
+            <property name="can_focus">False</property>
+            <property name="layout_style">end</property>
+            <child>
+              <placeholder/>
+            </child>
+            <child>
+              <placeholder/>
+            </child>
+          </object>
+          <packing>
+            <property name="expand">False</property>
+            <property name="fill">False</property>
+            <property name="position">0</property>
+          </packing>
+        </child>
+        <child>
+          <object class="GtkScrolledWindow">
+            <property name="visible">True</property>
+            <property name="can_focus">True</property>
+            <property name="hscrollbar_policy">never</property>
+            <property name="min_content_height">250</property>
+            <property name="propagate_natural_width">True</property>
+            <child>
+              <object class="GtkViewport">
+                <property name="visible">True</property>
+                <property name="can_focus">False</property>
+                <child>
+                  <object class="GtkBox">
+                    <property name="visible">True</property>
+                    <property name="can_focus">False</property>
+                    <property name="valign">start</property>
+                    <property name="margin_left">50</property>
+                    <property name="margin_right">50</property>
+                    <property name="margin_top">22</property>
+                    <property name="margin_bottom">22</property>
+                    <property name="hexpand">True</property>
+                    <property name="vexpand">False</property>
+                    <property name="orientation">vertical</property>
+                    <property name="spacing">18</property>
+                    <child>
+                      <object class="GtkGrid">
+                        <property name="visible">True</property>
+                        <property name="can_focus">False</property>
+                        <property name="halign">center</property>
+                        <property name="row_spacing">6</property>
+                        <property name="column_spacing">12</property>
+                        <child>
+                          <object class="GtkLabel">
+                            <property name="visible">True</property>
+                            <property name="can_focus">False</property>
+                            <property name="halign">end</property>
+                            <property name="label" translatable="yes">PDO Power</property>
+                            <style>
+                              <class name="dim-label"/>
+                            </style>
+                          </object>
+                          <packing>
+                            <property name="left_attach">0</property>
+                            <property name="top_attach">0</property>
+                          </packing>
+                        </child>
+                        <child>
+                          <object class="GtkLabel">
+                            <property name="visible">True</property>
+                            <property name="can_focus">False</property>
+                            <property name="halign">end</property>
+                            <property name="valign">start</property>
+                            <property name="label" translatable="yes">Information</property>
+                            <style>
+                              <class name="dim-label"/>
+                            </style>
+                          </object>
+                          <packing>
+                            <property name="left_attach">0</property>
+                            <property name="top_attach">1</property>
+                          </packing>
+                        </child>
+                        <child>
+                          <object class="GtkLabel" id="power-label">
+                            <property name="visible">True</property>
+                            <property name="can_focus">False</property>
+                            <property name="halign">start</property>
+                            <property name="valign">center</property>
+                            <property name="label" translatable="yes">label</property>
+                          </object>
+                          <packing>
+                            <property name="left_attach">1</property>
+                            <property name="top_attach">0</property>
+                          </packing>
+                        </child>
+                        <child>
+                          <object class="GtkLabel" id="info-label">
+                            <property name="visible">True</property>
+                            <property name="can_focus">False</property>
+                            <property name="label" translatable="yes">label
+test
+asdf</property>
+                          </object>
+                          <packing>
+                            <property name="left_attach">1</property>
+                            <property name="top_attach">1</property>
+                          </packing>
+                        </child>
+                      </object>
+                      <packing>
+                        <property name="expand">False</property>
+                        <property name="fill">True</property>
+                        <property name="position">0</property>
+                      </packing>
+                    </child>
+                    <child>
+                      <object class="GtkFrame">
+                        <property name="visible">True</property>
+                        <property name="can_focus">False</property>
+                        <property name="label_xalign">0</property>
+                        <property name="shadow_type">in</property>
+                        <child>
+                          <object class="GtkAlignment">
+                            <property name="visible">True</property>
+                            <property name="can_focus">False</property>
+                            <child>
+                              <object class="GtkListBox" id="src-cap-list">
+                                <property name="width_request">300</property>
+                                <property name="visible">True</property>
+                                <property name="can_focus">False</property>
+                                <property name="selection_mode">none</property>
+                                <property name="activate_on_single_click">False</property>
+                                <child>
+                                  <object class="GtkListBoxRow">
+                                    <property name="visible">True</property>
+                                    <property name="can_focus">False</property>
+                                    <property name="activatable">False</property>
+                                    <property name="selectable">False</property>
+                                    <child>
+                                      <object class="GtkBox">
+                                        <property name="visible">True</property>
+                                        <property name="can_focus">False</property>
+                                        <property name="margin_left">12</property>
+                                        <property name="margin_right">12</property>
+                                        <property name="margin_top">6</property>
+                                        <property name="margin_bottom">6</property>
+                                        <property name="spacing">12</property>
+                                        <property name="homogeneous">True</property>
+                                        <child>
+                                          <object class="GtkLabel" id="pdo-type">
+                                            <property name="visible">True</property>
+                                            <property name="can_focus">False</property>
+                                            <property name="halign">start</property>
+                                            <property name="label" translatable="yes">Fixed</property>
+                                          </object>
+                                          <packing>
+                                            <property name="expand">True</property>
+                                            <property name="fill">True</property>
+                                            <property name="position">0</property>
+                                          </packing>
+                                        </child>
+                                        <child>
+                                          <object class="GtkLabel" id="pdo-center">
+                                            <property name="visible">True</property>
+                                            <property name="can_focus">False</property>
+                                            <property name="halign">end</property>
+                                            <property name="label" translatable="yes">5 V</property>
+                                          </object>
+                                          <packing>
+                                            <property name="expand">True</property>
+                                            <property name="fill">True</property>
+                                            <property name="position">1</property>
+                                          </packing>
+                                        </child>
+                                        <child>
+                                          <object class="GtkBox">
+                                            <property name="visible">True</property>
+                                            <property name="can_focus">False</property>
+                                            <property name="halign">end</property>
+                                            <property name="spacing">6</property>
+                                            <child>
+                                              <object class="GtkLabel" id="pdo-right">
+                                                <property name="visible">True</property>
+                                                <property name="can_focus">False</property>
+                                                <property name="label" translatable="yes">3 A</property>
+                                              </object>
+                                              <packing>
+                                                <property name="expand">False</property>
+                                                <property name="fill">True</property>
+                                                <property name="pack_type">end</property>
+                                                <property name="position">0</property>
+                                              </packing>
+                                            </child>
+                                            <child>
+                                              <object class="GtkImage" id="pdo-icon">
+                                                <property name="visible">True</property>
+                                                <property name="can_focus">False</property>
+                                                <property name="tooltip_text" translatable="yes">Something something peak current
+another line about peak current</property>
+                                                <property name="icon_name">dialog-information-symbolic</property>
+                                              </object>
+                                              <packing>
+                                                <property name="expand">False</property>
+                                                <property name="fill">True</property>
+                                                <property name="pack_type">end</property>
+                                                <property name="position">1</property>
+                                              </packing>
+                                            </child>
+                                          </object>
+                                          <packing>
+                                            <property name="expand">True</property>
+                                            <property name="fill">True</property>
+                                            <property name="pack_type">end</property>
+                                            <property name="position">2</property>
+                                          </packing>
+                                        </child>
+                                      </object>
+                                    </child>
+                                  </object>
+                                </child>
+                                <child>
+                                  <object class="GtkListBoxRow">
+                                    <property name="visible">True</property>
+                                    <property name="can_focus">False</property>
+                                    <property name="activatable">False</property>
+                                    <property name="selectable">False</property>
+                                    <child>
+                                      <object class="GtkBox">
+                                        <property name="visible">True</property>
+                                        <property name="can_focus">False</property>
+                                        <property name="margin_left">12</property>
+                                        <property name="margin_right">12</property>
+                                        <property name="margin_top">6</property>
+                                        <property name="margin_bottom">6</property>
+                                        <property name="spacing">12</property>
+                                        <property name="homogeneous">True</property>
+                                        <child>
+                                          <object class="GtkLabel" id="pdo-type1">
+                                            <property name="visible">True</property>
+                                            <property name="can_focus">False</property>
+                                            <property name="halign">start</property>
+                                            <property name="label" translatable="yes">Battery</property>
+                                          </object>
+                                          <packing>
+                                            <property name="expand">True</property>
+                                            <property name="fill">True</property>
+                                            <property name="position">0</property>
+                                          </packing>
+                                        </child>
+                                        <child>
+                                          <object class="GtkLabel" id="pdo-center1">
+                                            <property name="visible">True</property>
+                                            <property name="can_focus">False</property>
+                                            <property name="halign">end</property>
+                                            <property name="label" translatable="yes">6–8.4 V</property>
+                                          </object>
+                                          <packing>
+                                            <property name="expand">True</property>
+                                            <property name="fill">True</property>
+                                            <property name="position">1</property>
+                                          </packing>
+                                        </child>
+                                        <child>
+                                          <object class="GtkBox">
+                                            <property name="visible">True</property>
+                                            <property name="can_focus">False</property>
+                                            <property name="halign">end</property>
+                                            <property name="spacing">6</property>
+                                            <child>
+                                              <object class="GtkLabel" id="pdo-right1">
+                                                <property name="visible">True</property>
+                                                <property name="can_focus">False</property>
+                                                <property name="label" translatable="yes">18 W</property>
+                                              </object>
+                                              <packing>
+                                                <property name="expand">False</property>
+                                                <property name="fill">True</property>
+                                                <property name="pack_type">end</property>
+                                                <property name="position">0</property>
+                                              </packing>
+                                            </child>
+                                            <child>
+                                              <object class="GtkImage" id="pdo-icon1">
+                                                <property name="can_focus">False</property>
+                                                <property name="icon_name">dialog-information-symbolic</property>
+                                              </object>
+                                              <packing>
+                                                <property name="expand">False</property>
+                                                <property name="fill">True</property>
+                                                <property name="pack_type">end</property>
+                                                <property name="position">1</property>
+                                              </packing>
+                                            </child>
+                                          </object>
+                                          <packing>
+                                            <property name="expand">True</property>
+                                            <property name="fill">True</property>
+                                            <property name="pack_type">end</property>
+                                            <property name="position">2</property>
+                                          </packing>
+                                        </child>
+                                      </object>
+                                    </child>
+                                  </object>
+                                </child>
+                              </object>
+                            </child>
+                          </object>
+                        </child>
+                        <child type="label_item">
+                          <placeholder/>
+                        </child>
+                      </object>
+                      <packing>
+                        <property name="expand">False</property>
+                        <property name="fill">False</property>
+                        <property name="position">1</property>
+                      </packing>
+                    </child>
+                  </object>
+                </child>
+              </object>
+            </child>
+          </object>
+          <packing>
+            <property name="expand">True</property>
+            <property name="fill">True</property>
+            <property name="position">1</property>
+          </packing>
+        </child>
+      </object>
+    </child>
+    <child>
+      <placeholder/>
+    </child>
+  </object>
+</interface>

pd-buddy-gtk.py

                 s = "No Source_Capabilities"
             flags = Gtk.DialogFlags.DESTROY_WITH_PARENT;
             window = self.builder.get_object("pdb-window")
-            dialog = Gtk.MessageDialog(window,
-                             flags,
-                             Gtk.MessageType.INFO,
-                             Gtk.ButtonsType.CLOSE,
-                             None)
-            dialog.set_markup("<span font_family='monospace'>{}</span>".format(s))
+            dialog_builder = Gtk.Builder.new_from_file("data/src-cap-dialog.ui")
+            dialog = dialog_builder.get_object("src-cap-dialog")
+            dialog.set_transient_for(window)
+            #dialog = Gtk.MessageDialog(window,
+            #                 flags,
+            #                 Gtk.MessageType.INFO,
+            #                 Gtk.ButtonsType.CLOSE,
+            #                 None)
+            #dialog.set_markup("<span font_family='monospace'>{}</span>".format(s))
             dialog.run()
             dialog.destroy()
 
     def do_startup(self):
         Gtk.Application.do_startup(self)
 
-        self.builder = Gtk.Builder()
-        self.builder.add_from_file("data/pd-buddy-gtk.ui")
+        self.builder = Gtk.Builder.new_from_file("data/pd-buddy-gtk.ui")
         self.builder.connect_signals(Handler(self.builder))
 
     def do_activate(self):