WM: Application Templates

This adds the ability to switch between different application-configurations
without interfering with Blender's normal operation.

This commit doesn't include any templates,
so its mostly to allow collaboration for the Blender 101 project
and other custom configurations.

Application templates can be installed & selected from the file menu.

Other details:

- The `bl_app_template_utils` module handles template activation
  (similar to `addon_utils`).
- The `bl_app_override` module is a general module
  to assist scripts overriding parts of Blender in reversible way.

See docs:
https://docs.blender.org/manual/en/dev/advanced/app_templates.html

See patch: D2565

1 files changed, 39 insertions, 0 deletions

diff --git a/release/scripts/modules/bpy/utils/__init__.py b/release/scripts/modules/bpy/utils/__init__.py
index 31dd836e034..65a2f278465 100644
--- a/release/scripts/modules/bpy/utils/__init__.py
+++ b/release/scripts/modules/bpy/utils/__init__.py
@@ -32,6 +32,7 @@ __all__ = (
     "preset_find",
     "preset_paths",
     "refresh_script_paths",
+    "app_template_paths",
     "register_class",
     "register_module",
     "register_manual_map",
@@ -245,6 +246,12 @@ def load_scripts(reload_scripts=False, refresh_scripts=False):
                     for mod in modules_from_path(path, loaded_modules):
                         test_register(mod)
 
+    # load template (if set)
+    if any(_bpy.utils.app_template_paths()):
+        import bl_app_template_utils
+        bl_app_template_utils.reset(reload_scripts=reload_scripts)
+        del bl_app_template_utils
+
     # deal with addons separately
     _initialize = getattr(_addon_utils, "_initialize", None)
     if _initialize is not None:
@@ -356,6 +363,38 @@ def refresh_script_paths():
             _sys_path_ensure(path)
 
 
+def app_template_paths(subdir=None):
+    """
+    Returns valid application template paths.
+
+    :arg subdir: Optional subdir.
+    :type subdir: string
+    :return: app template paths.
+    :rtype: generator
+    """
+
+    # note: LOCAL, USER, SYSTEM order matches script resolution order.
+    subdir_tuple = (subdir,) if subdir is not None else ()
+
+    path = _os.path.join(*(
+        resource_path('LOCAL'), "scripts", "startup",
+        "bl_app_templates_user", *subdir_tuple))
+    if _os.path.isdir(path):
+        yield path
+    else:
+        path = _os.path.join(*(
+            resource_path('USER'), "scripts", "startup",
+            "bl_app_templates_user", *subdir_tuple))
+        if _os.path.isdir(path):
+            yield path
+
+    path = _os.path.join(*(
+        resource_path('SYSTEM'), "scripts", "startup",
+        "bl_app_templates_system", *subdir_tuple))
+    if _os.path.isdir(path):
+        yield path
+
+
 def preset_paths(subdir):
     """
     Returns a list of paths for a specific preset.