Asset System: Prepare File Browser backend for the Asset Browser

The Asset Browser will be a sub-editor of the File Browser. This prepares the
File Browser code for that.

**File-Lists**
* Support loading assets with metadata read from external files into the
  file-list.
* New main based file-list type, for the "Current File" asset library.
* Refresh file-list when switching between browse modes or asset libraries.
* Support empty file-lists (asset library with no assets).
* Store file previews as icons, so scripts can reference them via icon-id. See
  previous commit.

**Space Data**
* Introduce "browse mode" to differeniate between file and asset browsing.
* Add `FileAssetSelectParams` to `SpaceFile`, with `FileSelectParams` as base.
  Makes sure data is separated between asset and file browsing when switching
  between them. The active params can be obtained through
  `ED_fileselect_get_active_params()`.
* `FileAssetSelectParams` stores the currently visible asset library ID.
* Introduce file history abstraction so file and asset browsing can keep a
  separate history (previous and next directories).

**General**
* Option to only show asset data-blocks while file browsing (not exposed here).
* Add "active_file" context member, so scripts can get and display info about
  the active file.
* Add "active_id" context member, so `ED_OT_lib_id_load_custom_preview` can set
  a custom ID preview. (Only for "Current File" asset library)
* Expose some of `FileDirEntry` in RNA as (non-editable). That way scripts can
  obtain name, preview icon and asset-data.

Part of the first Asset Browser milestone. Check the #asset_browser_milestone_1
project milestone on developer.blender.org.

Differential Revision: https://developer.blender.org/D9724

Reviewed by: Bastien Montagne

1 files changed, 5 insertions, 2 deletions

diff --git a/source/blender/editors/include/ED_fileselect.h b/source/blender/editors/include/ED_fileselect.h
index a5a8df916d6..3288cf11cb0 100644
--- a/source/blender/editors/include/ED_fileselect.h
+++ b/source/blender/editors/include/ED_fileselect.h
@@ -29,6 +29,7 @@ extern "C" {
 
 struct ARegion;
 struct FileSelectParams;
+struct FileAssetSelectParams;
 struct Scene;
 struct ScrArea;
 struct SpaceFile;
@@ -103,14 +104,14 @@ struct rcti;
 
 struct FileSelectParams *ED_fileselect_ensure_active_params(struct SpaceFile *sfile);
 struct FileSelectParams *ED_fileselect_get_active_params(const struct SpaceFile *sfile);
+struct FileSelectParams *ED_fileselect_get_file_params(const struct SpaceFile *sfile);
+struct FileAssetSelectParams *ED_fileselect_get_asset_params(const struct SpaceFile *sfile);
 
 void ED_fileselect_set_params_from_userdef(struct SpaceFile *sfile);
 void ED_fileselect_params_to_userdef(struct SpaceFile *sfile,
                                      const int temp_win_size[],
                                      const bool is_maximized);
 
-void ED_fileselect_reset_params(struct SpaceFile *sfile);
-
 void ED_fileselect_init_layout(struct SpaceFile *sfile, struct ARegion *region);
 
 FileLayout *ED_fileselect_get_layout(struct SpaceFile *sfile, struct ARegion *region);
@@ -142,6 +143,8 @@ void ED_fileselect_exit(struct wmWindowManager *wm,
                         struct Scene *owner_scene,
                         struct SpaceFile *sfile);
 
+bool ED_fileselect_is_asset_browser(const struct SpaceFile *sfile);
+
 void ED_fileselect_window_params_get(const struct wmWindow *win,
                                      int win_size[2],
                                      bool *is_maximized);