Make canvas draggable with mouse middle-click

Closes #292

.gitignore

@@ -59,6 +59,7 @@ ui_*.py
 source/canvaspreviewframe.py
 source/carla_config.py
 source/digitalpeakmeter.py
+source/draggablegraphicsview.py
 source/ledbutton.py
 source/paramspinbox.py
 source/pianoroll.py

Makefile

@@ -266,6 +266,7 @@ RES = \
 	bin/resources/carla_widgets.py \
 	bin/resources/canvaspreviewframe.py \
 	bin/resources/digitalpeakmeter.py \
+	bin/resources/draggablegraphicsview.py \
 	bin/resources/externalui.py \
 	bin/resources/ledbutton.py \
 	bin/resources/paramspinbox.py \
@@ -354,6 +355,7 @@ endif
 WIDGETS = \
 	source/canvaspreviewframe.py \
 	source/digitalpeakmeter.py \
+	source/draggablegraphicsview.py \
 	source/ledbutton.py \
 	source/paramspinbox.py \
 	source/pianoroll.py \
@@ -628,6 +630,7 @@ endif
 	$(LINK) $(DATADIR)/carla/carla_widgets.py            $(DESTDIR)$(DATADIR)/carla/resources
 	$(LINK) $(DATADIR)/carla/canvaspreviewframe.py       $(DESTDIR)$(DATADIR)/carla/resources
 	$(LINK) $(DATADIR)/carla/digitalpeakmeter.py         $(DESTDIR)$(DATADIR)/carla/resources
+	$(LINK) $(DATADIR)/carla/draggablegraphicsview.py    $(DESTDIR)$(DATADIR)/carla/resources
 	$(LINK) $(DATADIR)/carla/externalui.py               $(DESTDIR)$(DATADIR)/carla/resources
 	$(LINK) $(DATADIR)/carla/ledbutton.py                $(DESTDIR)$(DATADIR)/carla/resources
 	$(LINK) $(DATADIR)/carla/paramspinbox.py             $(DESTDIR)$(DATADIR)/carla/resources

resources/ui/carla_host.ui

@@ -127,7 +127,7 @@
          <number>1</number>
         </property>
         <item row="0" column="1">
-         <widget class="QGraphicsView" name="graphicsView"/>
+         <widget class="DraggableGraphicsView" name="graphicsView"/>
         </item>
         <item row="0" column="2">
          <widget class="DigitalPeakMeter" name="peak_out" native="true"/>
@@ -864,6 +864,11 @@
    <extends>QListWidget</extends>
    <header>racklistwidget.h</header>
   </customwidget>
+  <customwidget>
+   <class>DraggableGraphicsView</class>
+   <extends>QGraphicsView</extends>
+   <header>draggablegraphicsview.h</header>
+  </customwidget>
  </customwidgets>
  <resources>
   <include location="../resources.qrc"/>

source/widgets/draggablegraphicsview.py

@@ -0,0 +1,58 @@
+#!/usr/bin/env python3
+# -*- coding: utf-8 -*-
+
+# Middle-click draggable QGraphicsView
+# Copyright (C) 2016 Filipe Coelho <falktx@falktx.com>
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License as
+# published by the Free Software Foundation; either version 2 of
+# the License, or any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+# GNU General Public License for more details.
+#
+# For a full copy of the GNU General Public License see the doc/GPL.txt file.
+
+# ------------------------------------------------------------------------------------------------------------
+# Imports (Config)
+
+from carla_config import *
+
+# ------------------------------------------------------------------------------------------------------------
+# Imports (Global)
+
+if config_UseQt5:
+    from PyQt5.QtCore import Qt
+    from PyQt5.QtGui import QCursor
+    from PyQt5.QtWidgets import QGraphicsView, QMouseEvent
+else:
+    from PyQt4.QtCore import Qt
+    from PyQt4.QtGui import QCursor, QGraphicsView, QMouseEvent
+
+# ------------------------------------------------------------------------------------------------------------
+# Widget Class
+
+class DraggableGraphicsView(QGraphicsView):
+    def __init__(self, parent):
+        QGraphicsView.__init__(self, parent)
+
+        self.fPanning = False
+
+    def mousePressEvent(self, event):
+        if event.button() == Qt.MiddleButton:
+            self.fPanning = True
+            self.setDragMode(QGraphicsView.ScrollHandDrag)
+            event = QMouseEvent(event.type(), event.pos(), Qt.LeftButton, Qt.LeftButton, event.modifiers())
+
+        QGraphicsView.mousePressEvent(self, event)
+
+    def mouseReleaseEvent(self, event):
+        if self.fPanning:
+            self.fPanning = False
+            self.setDragMode(QGraphicsView.NoDrag)
+            self.setCursor(QCursor(Qt.ArrowCursor))
+
+        QGraphicsView.mouseReleaseEvent(self, event)