VSE: Add Compositor modifier

This patch adds a new Compositor modifier that applies a compositing
node group on a sequencer strip. This patch also introduces the concept
of a compositor node tree space subtype, where we now have a Scene and a
Sequencer subtypes. Practically, this just means that node like the
Render Layers node will not be available in the node editor in the
Sequencer subtype.

Future improvements includes:

- The compositor context is recreated on every modifier application,
  while it should ideally be persistent somehow to make use of the
  compositor static cache. This might require work from the compositor
  side by moving the static cache outside of the context and make it
  thread safe if needed. See `Render.compositor` for an example on
  persistent context.
- GPU execution is not supported. This just needs a GPU context to be
  bound before execution, but the tricky part is getting a GPU context.
  See `render::Compositor::execute` for an example on bounding a GPU
  context and why it is less straight forward.
- Node inputs are not exposed on the sequencer modifier interface. An
  approach similar to Geometry Nodes modifier could be used, look at
  `update_input_properties_from_node_tree` for reference, but notice
  that Geometry Nodes naturally exempt the main Geometry socket because
  Geometry inputs can't be exposed, but for the compositor, we will have
  to exempt the main Color and Mask sockets manually. !145971

Co-authored-by: Aras Pranckevicius <aras@nesnausk.org>
Co-authored-by: Falk David <falk@blender.org>
Pull Request: https://projects.blender.org/blender/blender/pulls/139634

scripts/startup/bl_ui/node_add_menu_compositor.py

@@ -49,7 +49,8 @@ class NODE_MT_compositor_node_input_scene_base(node_add_menu.NodeMenu):
 
     def draw(self, context):
         layout = self.layout
-        self.node_operator(layout, "CompositorNodeRLayers")
+        if context.space_data.node_tree_sub_type == 'SCENE':
+            self.node_operator(layout, "CompositorNodeRLayers")
         self.node_operator_with_outputs(context, layout, "CompositorNodeSceneTime", ["Frame", "Seconds"])
         self.node_operator(layout, "CompositorNodeTime")
 
@@ -60,12 +61,12 @@ class NODE_MT_compositor_node_output_base(node_add_menu.NodeMenu):
     bl_label = "Output"
 
     def draw(self, context):
-        del context
         layout = self.layout
         self.node_operator(layout, "NodeGroupOutput")
         self.node_operator(layout, "CompositorNodeViewer")
-        layout.separator()
-        self.node_operator(layout, "CompositorNodeOutputFile")
+        if context.space_data.node_tree_sub_type == 'SCENE':
+            layout.separator()
+            self.node_operator(layout, "CompositorNodeOutputFile")
 
         self.draw_assets_for_catalog(layout, self.bl_label)
 

scripts/startup/bl_ui/space_node.py

@@ -145,13 +145,29 @@ class NODE_HT_header(Header):
                     layout.template_ID(id_from, "active_texture", new="texture.new")
 
         elif snode.tree_type == 'CompositorNodeTree':
-
+            layout.prop(snode, "node_tree_sub_type", text="")
             NODE_MT_editor_menus.draw_collapsible(context, layout)
-
             layout.separator_spacer()
-            row = layout.row()
-            row.enabled = not snode.pin
-            row.template_ID(scene, "compositing_node_group", new="node.new_compositing_node_group")
+
+            if snode.node_tree_sub_type == 'SCENE':
+                row = layout.row()
+                row.enabled = not snode.pin
+                row.template_ID(scene, "compositing_node_group", new="node.new_compositing_node_group")
+            elif snode.node_tree_sub_type == 'SEQUENCER':
+                row = layout.row()
+                sequencer_scene = context.workspace.sequencer_scene
+                sequencer_editor = sequencer_scene.sequence_editor if sequencer_scene else None
+                active_strip = sequencer_editor.active_strip if sequencer_editor else None
+                active_modifier = active_strip.modifiers.active if active_strip else None
+                is_compositor_modifier_active = active_modifier and active_modifier.type == 'COMPOSITOR'
+                if is_compositor_modifier_active and not snode.pin:
+                    row.template_ID(
+                        active_modifier,
+                        "node_group",
+                        new="node.new_compositor_sequencer_node_group")
+                else:
+                    row.enabled = False
+                    row.template_ID(snode, "node_tree", new="node.new_compositor_sequencer_node_group")
 
         elif snode.tree_type == 'GeometryNodeTree':
             layout.prop(snode, "node_tree_sub_type", text="")
@@ -200,7 +216,7 @@ class NODE_HT_header(Header):
             op.parent_tree_index = len(snode.path) - 2
 
         # Backdrop
-        if is_compositor:
+        if is_compositor and snode.node_tree_sub_type == 'SCENE':
             row = layout.row(align=True)
             row.prop(snode, "show_backdrop", toggle=True)
             row.active = snode.node_tree is not None

scripts/startup/bl_ui/space_sequencer.py

@@ -1571,6 +1571,7 @@ class SEQUENCER_MT_modifier_add(Menu):
         else:
             self.operator_modifier_add(layout, 'BRIGHT_CONTRAST')
             self.operator_modifier_add(layout, 'COLOR_BALANCE')
+            self.operator_modifier_add(layout, 'COMPOSITOR')
             self.operator_modifier_add(layout, 'CURVES')
             self.operator_modifier_add(layout, 'HUE_CORRECT')
             self.operator_modifier_add(layout, 'MASK')