Minimise the need to batch operations in PlainEditor (#192)

The current design of `PlainEditor` and `PlainEditorTransaction` is that
if the editor is accessible, the inner layout is always valid and
up-to-date (barring a caught panic in the `transact` method). This is
not ideal for Masonry, because it forces event handling to recreate the
full layout even if the old version could be reused; this potential
reuse is especially prevalent in updates driven by Xilem.

This does bring in another change from Masonry, which is `StyleSet`;
this is a set of style properties, differentiated by their kind. It can
contain at most one font size, line height, etc.
This has some potentially unexpected behaviour with `FontStack`s, as in
the other APIs they "combine", but in this format they. However, this
combining behaviour is not documented as far as I can see, so I think
it's reasonable.
This implemented using a hashmap of discriminants in the enum.
The current API of `Arc<[StyleProperty]>` is horrendously unergonomic.

To reflect this change, I've renamed `PlainEditorTxn` to
`PlainEditorDriver`. Suggestions for an alternative name are welcome.

---------

Co-authored-by: Tom Churchman <[email protected]>

CHANGELOG.md

@@ -21,6 +21,11 @@ This release has an [MSRV] of 1.75.
 
 - `Generation` on `PlainEditor` to help implement lazy drawing. ([#143] by [@xorgy])
 
+### Changed
+
+### Parley
+
+- Breaking change: `PlainEditor`'s semantics are no longer transactional ([#192][] by [@DJMcNab][])
 
 ## [0.2.0] - 2024-10-10
 
@@ -76,6 +81,7 @@ This release has an [MSRV] of 1.70.
 [MSRV]: README.md#minimum-supported-rust-version-msrv
 
 [@dfrg]: https://github.com/dfrg
+[@DJMcNab]: https://github.com/DJMcNab
 [@nicoburns]: https://github.com/nicoburns
 [@waywardmonkeys]: https://github.com/waywardmonkeys
 [@xorgy]: https://github.com/xorgy
@@ -93,6 +99,7 @@ This release has an [MSRV] of 1.70.
 [#126]: https://github.com/linebender/parley/pull/126
 [#129]: https://github.com/linebender/parley/pull/129
 [#143]: https://github.com/linebender/parley/pull/143
+[#192]: https://github.com/linebender/parley/pull/192
 
 [Unreleased]: https://github.com/linebender/parley/compare/v0.2.0...HEAD
 [0.2.0]: https://github.com/linebender/parley/releases/tag/v0.2.0

examples/vello_editor/src/main.rs

@@ -28,7 +28,6 @@ mod access_ids;
 use access_ids::{TEXT_INPUT_ID, WINDOW_ID};
 
 mod text;
-use parley::{GenericFamily, StyleProperty};
 
 const WINDOW_TITLE: &str = "Vello Text Editor";
 
@@ -114,15 +113,10 @@ impl ApplicationHandler<accesskit_winit::Event> for SimpleVelloApp<'_> {
         let access_adapter =
             accesskit_winit::Adapter::with_event_loop_proxy(&window, self.event_loop_proxy.clone());
         window.set_visible(true);
+        window.set_ime_allowed(true);
 
         let size = window.inner_size();
 
-        self.editor.transact(|txn| {
-            txn.set_scale(1.0);
-            txn.set_width(Some(size.width as f32 - 2f32 * text::INSET));
-            txn.set_text(text::LOREM);
-        });
-
         // Create a vello Surface
         let surface_future = {
             let surface = self
@@ -236,15 +230,9 @@ impl ApplicationHandler<accesskit_winit::Event> for SimpleVelloApp<'_> {
             WindowEvent::Resized(size) => {
                 self.context
                     .resize_surface(&mut render_state.surface, size.width, size.height);
-                self.editor.transact(|txn| {
-                    txn.set_scale(1.0);
-                    txn.set_width(Some(size.width as f32 - 2f32 * text::INSET));
-                    txn.set_default_style(Arc::new([
-                        StyleProperty::FontSize(32.0),
-                        StyleProperty::LineHeight(1.2),
-                        GenericFamily::SystemUi.into(),
-                    ]));
-                });
+                let editor = self.editor.editor();
+                editor.set_scale(1.0);
+                editor.set_width(Some(size.width as f32 - 2f32 * text::INSET));
                 render_state.window.request_redraw();
             }
 
@@ -352,7 +340,7 @@ fn main() -> Result<()> {
         renderers: vec![],
         state: RenderState::Suspended(None),
         scene: Scene::new(),
-        editor: text::Editor::default(),
+        editor: text::Editor::new(text::LOREM),
         last_drawn_generation: Default::default(),
         event_loop_proxy: event_loop.create_proxy(),
     };
@@ -361,7 +349,8 @@ fn main() -> Result<()> {
     event_loop
         .run_app(&mut app)
         .expect("Couldn't run event loop");
-    print!("{}", app.editor.text());
+    let text = app.editor.text();
+    print!("{text}");
     Ok(())
 }