1 files changed, 133 insertions, 0 deletions
diff --git a/source/blender/editors/interface/interface_view.cc b/source/blender/editors/interface/interface_view.cc
new file mode 100644
index 00000000000..b199ce9562e
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+++ b/source/blender/editors/interface/interface_view.cc
@@ -0,0 +1,133 @@
+/*
+ * 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; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * 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.
+ */
+
+/** \file
+ * \ingroup edinterface
+ *
+ * This part of the UI-View API is mostly needed to support persistent state of items within the
+ * view. Views are stored in #uiBlock's, and kept alive with it until after the next redraw. So we
+ * can compare the old view items with the new view items and keep state persistent for matching
+ * ones.
+ */
+
+#include <memory>
+#include <variant>
+
+#include "DNA_screen_types.h"
+
+#include "BLI_listbase.h"
+
+#include "interface_intern.h"
+
+#include "UI_interface.hh"
+#include "UI_tree_view.hh"
+
+using namespace blender;
+using namespace blender::ui;
+
+/**
+ * Wrapper to store views in a #ListBase. There's no `uiView` base class, we just store views as a
+ * #std::variant.
+ */
+struct ViewLink : public Link {
+  using TreeViewPtr = std::unique_ptr<AbstractTreeView>;
+
+  std::string idname;
+  /* Note: Can't use std::get() on this until minimum macOS deployment target is 10.14. */
+  std::variant<TreeViewPtr> view;
+};
+
+template<class T> T *get_view_from_link(ViewLink &link)
+{
+  auto *t_uptr = std::get_if<std::unique_ptr<T>>(&link.view);
+  return t_uptr ? t_uptr->get() : nullptr;
+}
+
+/**
+ * Override this for all available tree types.
+ */
+AbstractTreeView *UI_block_add_view(uiBlock &block,
+                                    StringRef idname,
+                                    std::unique_ptr<AbstractTreeView> tree_view)
+{
+  ViewLink *view_link = OBJECT_GUARDED_NEW(ViewLink);
+  BLI_addtail(&block.views, view_link);
+
+  view_link->view = std::move(tree_view);
+  view_link->idname = idname;
+
+  return get_view_from_link<AbstractTreeView>(*view_link);
+}
+
+void ui_block_free_views(uiBlock *block)
+{
+  LISTBASE_FOREACH_MUTABLE (ViewLink *, link, &block->views) {
+    OBJECT_GUARDED_DELETE(link, ViewLink);
+  }
+}
+
+/**
+ * \param x, y: Coordinate to find a tree-row item at, in window space.
+ */
+uiTreeViewItemHandle *UI_block_tree_view_find_item_at(const ARegion *region,
+                                                      const int x,
+                                                      const int y)
+{
+  uiButTreeRow *tree_row_but = (uiButTreeRow *)ui_tree_row_find_mouse_over(region, x, y);
+  if (!tree_row_but) {
+    return nullptr;
+  }
+
+  return tree_row_but->tree_item;
+}
+
+static StringRef ui_block_view_find_idname(const uiBlock &block, const AbstractTreeView &view)
+{
+  /* First get the idname the of the view we're looking for. */
+  LISTBASE_FOREACH (ViewLink *, view_link, &block.views) {
+    if (get_view_from_link<AbstractTreeView>(*view_link) == &view) {
+      return view_link->idname;
+    }
+  }
+
+  return {};
+}
+
+uiTreeViewHandle *ui_block_view_find_matching_in_old_block(const uiBlock *new_block,
+                                                           const uiTreeViewHandle *new_view_handle)
+{
+  const AbstractTreeView &needle_view = reinterpret_cast<const AbstractTreeView &>(
+      *new_view_handle);
+
+  uiBlock *old_block = new_block->oldblock;
+  if (!old_block) {
+    return nullptr;
+  }
+
+  StringRef idname = ui_block_view_find_idname(*new_block, needle_view);
+  if (idname.is_empty()) {
+    return nullptr;
+  }
+
+  LISTBASE_FOREACH (ViewLink *, old_view_link, &old_block->views) {
+    if (old_view_link->idname == idname) {
+      return reinterpret_cast<uiTreeViewHandle *>(
+          get_view_from_link<AbstractTreeView>(*old_view_link));
+    }
+  }
+
+  return nullptr;
+}