Add addon to help debugging new dependency graph

Useful for developers, technical users and TD's.

Works for both 2.7x and 2.8x series. In 2.7x series new tools are to be found in
the Scene buttons, Dependency Graph panel. In 2.8x this panel is in layer
buttons.

depsgraph_debug.py

+# ##### BEGIN GPL LICENSE BLOCK #####
+#
+#  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 (at your option) 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.
+#
+#  You should have received a copy of the GNU General Public License
+#  along with this program; if not, write to the Free Software Foundation,
+#  Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
+#
+# ##### END GPL LICENSE BLOCK #####
+
+import bpy
+from bpy.types import (
+        Operator,
+        Panel,
+        )
+from bpy.props import (StringProperty, )
+
+bl_info = {
+    "name": "Dependency Graph Debug",
+    "author": "Sergey Sharybin",
+    "version": (0, 1),
+    "blender": (2, 79, 0),
+    "description": "Various dependency graph debugging tools",
+    "warning": "",
+    "wiki_url": "",
+    "tracker_url": "",
+    "category": "Development"}
+
+
+def _get_depsgraph(context):
+    scene = context.scene
+    if bpy.app.version < (2, 80, 0,):
+        return scene.depsgraph
+    else:
+        scene_layer = scene.render_layers.active
+        return scene_layer.depsgraph
+
+
+class SCENE_OT_depsgraph_graphviz(Operator):
+    bl_idname = "scene.depsgraph_graphviz"
+    bl_label = "Save Depsgraph"
+    bl_description = "Save current scene's dependency graph to a graphviz file"
+
+    filepath = StringProperty(
+            name="File Path",
+            description="Filepath used for saving the file",
+            maxlen=1024,
+            subtype='FILE_PATH',
+            )
+
+    @classmethod
+    def poll(cls, context):
+        depsgraph = _get_depsgraph(context)
+        return depsgraph is not None
+
+    def invoke(self, context, event):
+        import os
+        if not self.filepath:
+            blend_filepath = context.blend_data.filepath
+            if not blend_filepath:
+                blend_filepath = "deg"
+            else:
+                blend_filepath = os.path.splitext(blend_filepath)[0]
+
+            self.filepath = blend_filepath + ".dot"
+
+        context.window_manager.fileselect_add(self)
+
+        return {'RUNNING_MODAL'}
+
+    def execute(self, context):
+        depsgraph = _get_depsgraph(context)
+        depsgraph.debug_graphviz(self.filepath)
+        return {'FINISHED'}
+
+
+class SCENE_OT_depsgraph_image(Operator):
+    bl_idname = "scene.depsgraph_image"
+    bl_label = "Depsgraph as Image"
+    bl_description = "Create new image datablock from the dependency graph"
+
+    def _getOrCreateImageForAbsPath(self, filepath):
+        for image in bpy.data.images:
+            if image.filepath == filepath:
+                image.reload()
+                return image
+        return bpy.data.images.load(filepath, check_existing=True)
+
+    def _findBestImageEditor(self, context, image):
+        first_none_editor = None
+        for area in context.screen.areas:
+            if area.type != 'IMAGE_EDITOR':
+                continue
+            for space in area.spaces:
+                if space.type != 'IMAGE_EDITOR':
+                    continue
+                if not space.image:
+                    first_none_editor = space
+                else:
+                    if space.image == image:
+                        return space
+        return first_none_editor
+
+    def execute(self, context):
+        import os
+        import subprocess
+        import tempfile
+        # Create temporary file.
+        fd, dot_filepath = tempfile.mkstemp(suffix=".dot")
+        os.close(fd)
+        # Save dependency graph to graphviz file.
+        depsgraph = _get_depsgraph(context)
+        depsgraph.debug_graphviz(dot_filepath)
+        # Convert graphviz to PNG image.
+        png_filepath = os.path.join(bpy.app.tempdir, "depsgraph.png")
+        command = ("dot", "-Tpng", dot_filepath, "-o", png_filepath)
+        image = None
+        try:
+            subprocess.run(command)
+            # Open image in Blender.
+            image = self._getOrCreateImageForAbsPath(png_filepath)
+        except:
+            self.report({'ERROR'}, "Error invoking dot command")
+            return {'CANCELLED'}
+        finally:
+            # Remove graphviz file.
+            os.remove(dot_filepath)
+        editor = self._findBestImageEditor(context, image)
+        if editor:
+            editor.image = image
+        return {'FINISHED'}
+
+
+class SCENE_PT_depsgraph(bpy.types.Panel):
+    bl_label = "Dependency Graph"
+    bl_space_type = "PROPERTIES"
+    bl_region_type = "WINDOW"
+    bl_context = "scene"
+    bl_options = {'DEFAULT_CLOSED'}
+
+    @classmethod
+    def poll(cls, context):
+        if bpy.app.version >= (2, 80, 0,):
+            return False
+        depsgraph = _get_depsgraph(context)
+        return depsgraph is not None
+
+    def draw(self, context):
+        layout = self.layout
+        layout.operator("scene.depsgraph_graphviz")
+        layout.operator("scene.depsgraph_image")
+
+
+class RENDERLAYER_PT_depsgraph(bpy.types.Panel):
+    bl_label = "Dependency Graph"
+    bl_space_type = "PROPERTIES"
+    bl_region_type = "WINDOW"
+    bl_context = "render_layer"
+    bl_options = {'DEFAULT_CLOSED'}
+
+    @classmethod
+    def poll(cls, context):
+        if bpy.app.version < (2, 80, 0,):
+            return False
+        depsgraph = _get_depsgraph(context)
+        return depsgraph is not None
+
+    def draw(self, context):
+        layout = self.layout
+        layout.operator("scene.depsgraph_graphviz")
+        layout.operator("scene.depsgraph_image")
+
+
+def register():
+    bpy.utils.register_class(SCENE_OT_depsgraph_graphviz)
+    bpy.utils.register_class(SCENE_OT_depsgraph_image)
+    bpy.utils.register_class(SCENE_PT_depsgraph)
+    bpy.utils.register_class(RENDERLAYER_PT_depsgraph)
+
+
+def unregister():
+    bpy.utils.unregister_class(SCENE_OT_depsgraph_graphviz)
+    bpy.utils.unregister_class(SCENE_OT_depsgraph_image)
+    bpy.utils.unregister_class(SCENE_PT_depsgraph)
+    bpy.utils.unregister_class(RENDERLAYER_PT_depsgraph)
+
+
+if __name__ == "__main__":
+    register()