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, 42 insertions, 0 deletions

diff --git a/source/blender/blenkernel/intern/appdir.c b/source/blender/blenkernel/intern/appdir.c
index 3fb8a147960..43fd47981b1 100644
--- a/source/blender/blenkernel/intern/appdir.c
+++ b/source/blender/blenkernel/intern/appdir.c
@@ -683,6 +683,48 @@ bool BKE_appdir_program_python_search(
 	return is_found;
 }
 
+static const char *app_template_directory_search[2] = {
+	"startup" SEP_STR "bl_app_templates_user",
+	"startup" SEP_STR "bl_app_templates_system",
+};
+
+static const int app_template_directory_id[2] = {
+	BLENDER_USER_SCRIPTS,
+	BLENDER_SYSTEM_SCRIPTS,
+};
+
+/**
+ * Return true if templates exist
+ */
+bool BKE_appdir_app_template_any(void)
+{
+	char temp_dir[FILE_MAX];
+	for (int i = 0; i < 2; i++) {
+		if (BKE_appdir_folder_id_ex(
+		        app_template_directory_id[i], app_template_directory_search[i],
+		        temp_dir, sizeof(temp_dir)))
+		{
+			return true;
+		}
+	}
+	return false;
+}
+
+bool BKE_appdir_app_template_id_search(const char *app_template, char *path, size_t path_len)
+{
+	for (int i = 0; i < 2; i++) {
+		char subdir[FILE_MAX];
+		BLI_join_dirfile(subdir, sizeof(subdir), app_template_directory_search[i], app_template);
+		if (BKE_appdir_folder_id_ex(
+		        app_template_directory_id[i], subdir,
+		        path, path_len))
+		{
+			return true;
+		}
+	}
+	return false;
+}
+
 /**
  * Gets the temp directory when blender first runs.
  * If the default path is not found, use try $TEMP