node_presets: add back from addons_contrib

Improve error handling:

- Show exception if the path can't be listed.
- Reload node cache if the preferences directory changes.

node_presets.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; version 2
+#  of the License.
+#
+#  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 #####
+
+bl_info = {
+    "name": "Node Presets",
+    "description": "Useful and time-saving tools for rendering workflow",
+    "author": "Campbell Barton",
+    "version": (1, 1),
+    "blender": (2, 80, 0),
+    "location": "Node > Add Template",
+    "description": "Adds node presets",
+    "warning": "",
+    "wiki_url": "",
+    "tracker_url": "https://developer.blender.org/maniphest/task/edit/form/2/",
+    "category": "Render",
+}
+
+import os
+import bpy
+from bpy.types import (
+    Operator,
+    Menu,
+    AddonPreferences,
+)
+
+from bpy.props import (
+    StringProperty,
+)
+
+
+# -----------------------------------------------------------------------------
+# Node Adding Operator
+
+
+def node_center(context):
+    from mathutils import Vector
+    loc = Vector((0.0, 0.0))
+    node_selected = context.selected_nodes
+    if node_selected:
+        for node in node_selected:
+            loc += node.location
+        loc /= len(node_selected)
+    return loc
+
+
+def node_template_add(context, filepath, node_group, ungroup, report):
+    """ Main function
+    """
+
+    space = context.space_data
+    node_tree = space.node_tree
+    node_active = context.active_node
+    node_selected = context.selected_nodes
+
+    if node_tree is None:
+        report({'ERROR'}, "No node tree available")
+        return
+
+    with bpy.data.libraries.load(filepath, link=False) as (data_from, data_to):
+        assert(node_group in data_from.node_groups)
+        data_to.node_groups = [node_group]
+    node_group = data_to.node_groups[0]
+
+    # add node!
+    center = node_center(context)
+
+    for node in node_tree.nodes:
+        node.select = False
+
+    node_type_string = {
+        "ShaderNodeTree": "ShaderNodeGroup",
+        "CompositorNodeTree": "CompositorNodeGroup",
+        "TextureNodeTree": "TextureNodeGroup",
+    }[type(node_tree).__name__]
+
+    node = node_tree.nodes.new(type=node_type_string)
+    node.node_tree = node_group
+
+    is_fail = (node.node_tree is None)
+    if is_fail:
+        report({'WARNING'}, "Incompatible node type")
+
+    node.select = True
+    node_tree.nodes.active = node
+    node.location = center
+
+    if is_fail:
+        node_tree.nodes.remove(node)
+    else:
+        if ungroup:
+            bpy.ops.node.group_ungroup()
+
+    # node_group.user_clear()
+    # bpy.data.node_groups.remove(node_group)
+
+
+# -----------------------------------------------------------------------------
+# Node Template Prefs
+
+def node_search_path(context):
+    preferences = context.preferences
+    addon_prefs = preferences.addons[__name__].preferences
+    dirpath = addon_prefs.search_path
+    return dirpath
+
+
+class NodeTemplatePrefs(AddonPreferences):
+    bl_idname = __name__
+
+    search_path: StringProperty(
+        name="Directory of blend files with node-groups",
+        subtype='DIR_PATH',
+    )
+
+    def draw(self, context):
+        layout = self.layout
+        layout.prop(self, "search_path")
+
+
+class NODE_OT_template_add(Operator):
+    """Add a node template"""
+    bl_idname = "node.template_add"
+    bl_label = "Add node group template"
+    bl_description = "Add node group template"
+    bl_options = {'REGISTER', 'UNDO'}
+
+    filepath: StringProperty(
+        subtype='FILE_PATH',
+    )
+    group_name: StringProperty()
+
+    def execute(self, context):
+        node_template_add(context, self.filepath, self.group_name, True, self.report)
+
+        return {'FINISHED'}
+
+    def invoke(self, context, event):
+        node_template_add(context, self.filepath, self.group_name, event.shift, self.report)
+
+        return {'FINISHED'}
+
+
+# -----------------------------------------------------------------------------
+# Node menu list
+
+def node_template_cache(context, *, reload=False):
+    dirpath = node_search_path(context)
+
+    if node_template_cache._node_cache_path != dirpath:
+        reload = True
+
+    node_cache = node_template_cache._node_cache
+    if reload:
+        node_cache = []
+    if node_cache:
+        return node_cache
+
+    for fn in os.listdir(dirpath):
+        if fn.endswith(".blend"):
+            filepath = os.path.join(dirpath, fn)
+            with bpy.data.libraries.load(filepath) as (data_from, data_to):
+                for group_name in data_from.node_groups:
+                    if not group_name.startswith("_"):
+                        node_cache.append((filepath, group_name))
+
+    node_template_cache._node_cache = node_cache
+    node_template_cache._node_cache_path = dirpath
+
+    return node_cache
+
+
+node_template_cache._node_cache = []
+node_template_cache._node_cache_path = ""
+
+
+class NODE_MT_template_add(Menu):
+    bl_label = "Node Template"
+
+    def draw(self, context):
+        layout = self.layout
+
+        dirpath = node_search_path(context)
+        if dirpath == "":
+            layout.label(text="Set search dir in the addon-prefs")
+            return
+
+        try:
+            node_items = node_template_cache(context)
+        except Exception as ex:
+            node_items = ()
+            layout.label(text=repr(ex), icon='ERROR')
+
+        for filepath, group_name in node_items:
+            props = layout.operator(
+                NODE_OT_template_add.bl_idname,
+                text=group_name,
+            )
+            props.filepath = filepath
+            props.group_name = group_name
+
+
+def add_node_button(self, context):
+    self.layout.menu(
+        NODE_MT_template_add.__name__,
+        text="Template",
+        icon='PLUGIN',
+    )
+
+
+classes = (
+    NODE_OT_template_add,
+    NODE_MT_template_add,
+    NodeTemplatePrefs
+)
+
+
+def register():
+    for cls in classes:
+        bpy.utils.register_class(cls)
+
+    bpy.types.NODE_MT_add.append(add_node_button)
+
+
+def unregister():
+    for cls in classes:
+        bpy.utils.unregister_class(cls)
+
+    bpy.types.NODE_MT_add.remove(add_node_button)
+
+
+if __name__ == "__main__":
+    register()