UI: Add initial "grid view"

Part of T98560.
See https://wiki.blender.org/wiki/Source/Interface/Views

Adds all the basic functionality needed for grid views. They display
items in a grid of rows and columns, typically with a preview image and
a label underneath. Think of the main region in the Asset Browser.

Current features:
- Active item
- Notifier listening (also added this to the tree view)
- Performance: Skip adding buttons that are not scrolled into view
  (solves performance problems for big asset libraries, for example).
- Custom item size
- Preview items (items that draw a preview with a label underneath)
- Margins between items scale so the entire region width is filled with
  column, rather than leaving a big empty block at the right if there's
  not enough space for another column (like the File and current Asset
Browser does it).
- "Data-View Item" theme colors. Not shown in the UI yet.

No user visible changes expected since the grid views aren't used for
anything yet.

This was developed as part of a rewrite of the Asset Browser UI
(`asset-browser-grid-view` branch), see T95653. There's no reason to
keep this part in a branch, continuing development in master makes
things easier.

Grid and tree views have a lot of very similar code, so I'm planning to
unify them to a degree. I kept things separate for the start to first
find out how much and what exactly makes sense to override.

1 files changed, 5 insertions, 1 deletions

diff --git a/source/blender/editors/include/UI_tree_view.hh b/source/blender/editors/include/UI_tree_view.hh
index 5504e426f34..1aeb13ca5cc 100644
--- a/source/blender/editors/include/UI_tree_view.hh
+++ b/source/blender/editors/include/UI_tree_view.hh
@@ -28,6 +28,7 @@ struct uiButTreeRow;
 struct uiLayout;
 struct wmDrag;
 struct wmEvent;
+struct wmNotifier;
 
 namespace blender::ui {
 
@@ -128,6 +129,9 @@ class AbstractTreeView : public TreeViewItemContainer {
 
   void foreach_item(ItemIterFn iter_fn, IterOptions options = IterOptions::None) const;
 
+  /** Listen to a notifier, returning true if a redraw is needed. */
+  virtual bool listen(const wmNotifier &) const;
+
   /** Only one item can be renamed at a time. */
   bool is_renaming() const;
 
@@ -185,7 +189,7 @@ class AbstractTreeViewItem : public TreeViewItemContainer {
   bool is_renaming_ = false;
 
  protected:
-  /** This label is used for identifying an item within its parent. */
+  /** This label is used as the default way to identifying an item within its parent. */
   std::string label_{};
   /** Every visible item gets a button of type #UI_BTYPE_TREEROW during the layout building. */
   uiButTreeRow *tree_row_but_ = nullptr;