Support snapping to edges as long as Alt is not pressed

xrandroll/main.py

@@ -346,6 +346,23 @@ class Window(QObject):
             mon["item"].update_visuals(mon)
         self.adjust_view()
 
+    def possible_snaps(self, name):
+        """Return two lists of values to which the x and y position
+        of monitor "name" could snap to."""
+        snaps_x = []
+        snaps_y = []
+
+        for monitor, data in self.xrandr_info.items():
+            if monitor == name:
+                continue
+            else:
+                mod_x, mod_y = [int(x) for x in data["current_mode"].split("x")]
+                snaps_x.append(data["pos_x"])
+                snaps_x.append(data["pos_x"] + mod_x)
+                snaps_y.append(data["pos_y"])
+                snaps_y.append(data["pos_y"] + mod_y)
+        return snaps_x, snaps_y
+
     def adjust_view(self):
         self.ui.sceneView.resetTransform()
         self.ui.sceneView.ensureVisible(self.scene.sceneRect(), 100, 100)

xrandroll/monitor_item.py

@@ -73,10 +73,21 @@ class MonitorItem(QGraphicsRectItem, QObject):
         self.window.pos_label.hide()
 
     def mouseMoveEvent(self, event):
+        snaps_x, snaps_y = self.window.possible_snaps(self.name)
         view = event.widget().parent()
         click_pos = event.buttonDownScreenPos(Qt.LeftButton)
         current_pos = event.screenPos()
-        self.setPos(
-            view.mapToScene(view.mapFromScene(self.orig_pos) + current_pos - click_pos)
-        )
+        new_pos = view.mapFromScene(self.orig_pos) + current_pos - click_pos
+        new_pos = view.mapToScene(new_pos)
+        if not event.modifiers() & Qt.AltModifier:
+            # Check for snaps
+            x = new_pos.x()
+            delta_x = min((abs(x - sx), i) for i, sx in enumerate(snaps_x))
+            if delta_x[0] < 50:  # snap
+                new_pos.setX(int(snaps_x[delta_x[1]]))
+            y = new_pos.y()
+            delta_y = min((abs(y - sy), i) for i, sy in enumerate(snaps_y))
+            if delta_y[0] < 50:  # snap
+                new_pos.setY(int(snaps_y[delta_y[1]]))
+        self.setPos(new_pos)
         self.window.show_pos(int(self.pos().x()), int(self.pos().y()))