Geometry Nodes: new Viewer node

This adds a viewer node similar to the one in the compositor.
The icon in the headers of nodes is removed because it served
the same purpose and is not necessary anymore.

Node outputs can be connected to the active viewer using
ctrl+shift+LMB, just like in the compositor. Right now this collides
with the shortcut used in the node wrangler addon, which will
be changed separately.

As of now, the viewed geometry is only visible in the spreadsheet.
Viewport visualization will be added separately.

There are a couple of benefits of using a viewer node compared
to the old approach with the icon in the node header:
* Better support for nodes that have more than one geometry output.
* It's more consistent with the compositor.
* If attributes become decoupled from geometry in the future,
  the viewer can have a separate input for the attribute to visualize.
* The viewer node could potentially have visualization settings.
* Allows to keep "visualization points" around by having multiple
  viewer nodes.
* Less visual clutter in node headers.

Differential Revision: https://developer.blender.org/D11470

release/scripts/startup/bl_operators/node.py

@@ -306,67 +306,6 @@ class NODE_OT_tree_path_parent(Operator):
         return {'FINISHED'}
 
 
-class NODE_OT_active_preview_toggle(Operator):
-    '''Toggle active preview state of node'''
-    bl_idname = "node.active_preview_toggle"
-    bl_label = "Toggle Active Preview"
-    bl_options = {'REGISTER', 'UNDO'}
-
-    @classmethod
-    def poll(cls, context):
-        space = context.space_data
-        if space is None:
-            return False
-        if space.type != 'NODE_EDITOR':
-            return False
-        if space.edit_tree is None:
-            return False
-        if space.edit_tree.nodes.active is None:
-            return False
-        return True
-
-    def execute(self, context):
-        node_editor = context.space_data
-        ntree = node_editor.edit_tree
-        active_node = ntree.nodes.active
-
-        if active_node.active_preview:
-            self._disable_preview(context, active_node)
-        else:
-            self._enable_preview(context, node_editor, ntree, active_node)
-
-        return {'FINISHED'}
-
-    @classmethod
-    def _enable_preview(cls, context, node_editor, ntree, active_node):
-        spreadsheets = cls._find_unpinned_spreadsheets(context)
-
-        for spreadsheet in spreadsheets:
-            spreadsheet.set_geometry_node_context(node_editor, active_node)
-
-        for node in ntree.nodes:
-            node.active_preview = False
-        active_node.active_preview = True
-
-    @classmethod
-    def _disable_preview(cls, context, active_node):
-        spreadsheets = cls._find_unpinned_spreadsheets(context)
-        for spreadsheet in spreadsheets:
-            spreadsheet.context_path.clear()
-
-        active_node.active_preview = False
-
-    @staticmethod
-    def _find_unpinned_spreadsheets(context):
-        spreadsheets = []
-        for window in context.window_manager.windows:
-            for area in window.screen.areas:
-                space = area.spaces.active
-                if space.type == 'SPREADSHEET' and not space.is_pinned:
-                    spreadsheets.append(space)
-        return spreadsheets
-
-
 classes = (
     NodeSetting,
 
@@ -375,5 +314,4 @@ classes = (
     NODE_OT_add_search,
     NODE_OT_collapse_hide_unused_toggle,
     NODE_OT_tree_path_parent,
-    NODE_OT_active_preview_toggle,
 )