Import a scene from an .mg file into the current graph

Add an "Import Scene" (Ctrl+Shift+I) option in the File menu
that allows to select an existing .mg file and import it in the
current graph.

The imported scene will automatically be placed below the lowest
existing node along the Y axis.

meshroom/ui/commands.py

@@ -7,7 +7,7 @@ from PySide2.QtCore import Property, Signal
 
 from meshroom.core.attribute import ListAttribute, Attribute
 from meshroom.core.graph import GraphModification
-from meshroom.core.node import nodeFactory
+from meshroom.core.node import nodeFactory, Position
 
 
 class UndoCommand(QUndoCommand):
@@ -216,6 +216,37 @@ class PasteNodeCommand(GraphCommand):
         self.graph.removeNode(self.nodeName)
 
 
+class ImportSceneCommand(GraphCommand):
+    """
+    Handle the import of a scene into a Graph.
+    """
+    def __init__(self, graph, filepath=None, yOffset=0, parent=None):
+        super(ImportSceneCommand, self).__init__(graph, parent)
+        self.filepath = filepath
+        self.importedNames = []
+        self.yOffset = yOffset
+
+    def redoImpl(self):
+        status = self.graph.load(self.filepath, setupProjectFile=False, importScene=True)
+        importedNodes = self.graph.importedNodes
+        self.setText("Import Scene ({} nodes)".format(importedNodes.count))
+
+        lowestY = 0
+        for node in self.graph.nodes:
+            if node not in importedNodes and node.y > lowestY:
+                lowestY = node.y
+
+        for node in importedNodes:
+            self.importedNames.append(node.name)
+            self.graph.node(node.name).position = Position(node.x, node.y + lowestY + self.yOffset)
+
+        return status
+
+    def undoImpl(self):
+        for nodeName in self.importedNames:
+            self.graph.removeNode(nodeName)
+        self.importedNames = []
+
 class SetAttributeCommand(GraphCommand):
     def __init__(self, graph, attribute, value, parent=None):
         super(SetAttributeCommand, self).__init__(graph, parent)