UI: Add AbstractView base class for views, unify reconstruction in there

No user visible changes expected.

There's plenty of duplicated code in the grid and the tree view, and I expect
this to become more. This starts the process of unifying these parts, which
should also make it easier to add new views. Complexity in the view classes is
reduced, and some type shenanigans for C compatibility and general view
management can be removed, since there is now a common base type.

For the start this ports some of the view reconstruction, where the view and
its items are compared to the version of itself in the previous redraw, so that
state (highlighted, active, renaming, collapsed, ...) can be preserved.
Notifier listening is also ported.

1 files changed, 52 insertions, 0 deletions

diff --git a/source/blender/editors/interface/abstract_view.cc b/source/blender/editors/interface/abstract_view.cc
new file mode 100644
index 00000000000..542d82a56a3
--- /dev/null
+++ b/source/blender/editors/interface/abstract_view.cc
@@ -0,0 +1,52 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+
+/** \file
+ * \ingroup edinterface
+ */
+
+#include "interface_intern.h"
+
+#include "UI_abstract_view.hh"
+
+namespace blender::ui {
+
+/* ---------------------------------------------------------------------- */
+/** \name View Reconstruction
+ * \{ */
+
+bool AbstractView::is_reconstructed() const
+{
+  return is_reconstructed_;
+}
+
+void AbstractView::update_from_old(uiBlock &new_block)
+{
+  uiBlock *old_block = new_block.oldblock;
+  if (!old_block) {
+    is_reconstructed_ = true;
+    return;
+  }
+
+  const uiViewHandle *old_view_handle = ui_block_view_find_matching_in_old_block(
+      &new_block, reinterpret_cast<uiViewHandle *>(this));
+  if (old_view_handle == nullptr) {
+    /* Initial construction, nothing to update. */
+    is_reconstructed_ = true;
+    return;
+  }
+
+  update_children_from_old(reinterpret_cast<const AbstractView &>(*old_view_handle));
+
+  /* Finished (re-)constructing the tree. */
+  is_reconstructed_ = true;
+}
+
+/** \} */
+
+bool AbstractView::listen(const wmNotifier & /*notifier*/) const
+{
+  /* Nothing by default. */
+  return false;
+}
+
+}  // namespace blender::ui