Blend: a pending pick starts over when the document's history changes

The Blend tool kept its first pick, its clicked anchor and the blend it
was adding to through edits made outside the tool. Picking A, recoloring
other art and clicking B made a blend of A and B; undoing A's creation
left the next click doing nothing.

History::step names the current step by the serial numbers of the newest
undo step and the next redo step. The session keeps the active document's
uid and step from the tool's last pointer event and calls the new
Tool::history_moved at the next pointer event, or before drawing
overlays, when they differ. The tool's own edits are recorded after its
actions; a selection tool lent by Cmd is not told. BlendTool clears its
pick and chain there, as Escape does. A selection change keeps them.

crates/engine/src/history.rs

@@ -19,6 +19,14 @@ pub struct HistoryEntry {
     next: usize,
     /// The template and name `label` was made from ([`Session::edit_named`]).
     pub(crate) named: Option<NamedStep>,
+    /// A number no other step takes ([`History::step`]).
+    serial: u64,
+}
+
+/// The next [`HistoryEntry::serial`]: 1 for the first step made, so 0 never names a step.
+fn next_serial() -> u64 {
+    static NEXT: std::sync::atomic::AtomicU64 = std::sync::atomic::AtomicU64::new(1);
+    NEXT.fetch_add(1, std::sync::atomic::Ordering::Relaxed)
 }
 
 /// A step name made by filling the `{name}` placeholder of a template with a name
@@ -45,7 +53,7 @@ impl HistoryEntry {
     pub(crate) fn kept(label: String, doc: Arc<Document>, selection: Arc<Selection>, next: &Document) -> Self {
         doc.drop_lookup_cache();
         let (bytes, next_bytes) = doc.retained_bytes_each(next);
-        HistoryEntry { label, doc, selection, bytes, next_bytes, next: std::ptr::from_ref(next) as usize, named: None }
+        HistoryEntry { label, doc, selection, bytes, next_bytes, next: std::ptr::from_ref(next) as usize, named: None, serial: next_serial() }
     }
 
     /// The template and name the step's label was made from, while the label is still the one
@@ -66,7 +74,16 @@ impl HistoryEntry {
             return Self::kept(label, doc, selection, now);
         }
         doc.drop_lookup_cache();
-        HistoryEntry { label, doc, selection, bytes: costs.next_bytes, next_bytes: costs.bytes, next: Arc::as_ptr(now) as usize, named: None }
+        HistoryEntry {
+            label,
+            doc,
+            selection,
+            bytes: costs.next_bytes,
+            next_bytes: costs.bytes,
+            next: Arc::as_ptr(now) as usize,
+            named: None,
+            serial: next_serial(),
+        }
     }
 
     /// The figures [`HistoryEntry::turned`] reuses.
@@ -111,6 +128,13 @@ impl History {
         self.undo.iter().chain(&self.redo).map(|e| e.bytes).sum()
     }
 
+    /// Which step the document is at: the newest undo step and the next redo step, by numbers no
+    /// other step takes (0 for none). Every new step, Undo and Redo changes it; an edit merged into
+    /// the newest step (an undo group) and a selection change do not.
+    pub fn step(&self) -> (u64, u64) {
+        (self.undo.last().map_or(0, |e| e.serial), self.redo.last().map_or(0, |e| e.serial))
+    }
+
     /// Let the oldest steps go while over the step limit or the memory budget: undo steps first
     /// (the oldest), then redo steps (the furthest ahead).
     pub fn trim(&mut self) {

crates/engine/src/lib.rs

@@ -60,6 +60,10 @@ pub struct Session {
     /// While Cmd lends `tool` (a selection tool) for a drag: the tool it was lent to, which comes
     /// back as it was at the release ([`Session::pointer`]).
     pub(crate) lender: Option<Box<dyn Tool>>,
+    /// The active document (its uid) and its [`History::step`] when the tool last handled a pointer
+    /// event or drew its overlays: when they differ at the next one, the tool is told first
+    /// ([`vectorcraft_tools::Tool::history_moved`]). None until the first.
+    pub(crate) tool_step: Option<(u64, (u64, u64))>,
     /// The selection tool chosen last (Selection, Direct Selection or Group Selection): the one Cmd
     /// lends the other tools. None until one is chosen.
     pub(crate) last_selection_tool: Option<&'static str>,

crates/engine/src/session/documents.rs

@@ -31,6 +31,7 @@ impl Session {
             journal: Journal::default(),
             tool: vectorcraft_tools::create("selection"),
             lender: None,
+            tool_step: None,
             last_selection_tool: None,
             last_view: ViewInfo::default(),
             preview_memo: Default::default(),

crates/engine/src/tests/blendopts.rs

@@ -1,6 +1,6 @@
 //! Blend Options (defaults with nothing selected, `object.blend.info`) and the Blend tool:
 //! start points from clicked anchors, adding keys to a blend instead of nesting it (M8.18), and
-//! Escape dropping the first pick.
+//! Escape, or an edit made outside the tool, dropping the first pick.
 
 use serde_json::{Value, json};
 use vectorcraft_doc::live::{BlendOrientation, BlendSpacing, BlendSpec};
@@ -167,6 +167,78 @@ fn escape_drops_the_blend_tools_first_pick() {
     assert_eq!(spec(&s, g).0, vec![b, c], "a was not added");
 }
 
+#[test]
+fn an_edit_or_undo_made_outside_the_blend_tool_drops_its_first_pick() {
+    for undo in [false, true] {
+        let mut s = session();
+        let (a, b, c) = (rect(&mut s, 0.0, 0.0, 40.0), rect(&mut s, 200.0, 0.0, 40.0), rect(&mut s, 400.0, 0.0, 40.0));
+        s.select_tool("blend", ViewInfo::default()).unwrap();
+        let click = |s: &mut Session, x: f64, y: f64| s.pointer(&PointerEvent::new(PointerKind::Down, x, y), ViewInfo::default()).unwrap();
+        // Undo takes away c, the object picked first; an edit recolors c, which is not picked.
+        click(&mut s, if undo { 420.0 } else { 20.0 }, 20.0);
+        assert!(!s.overlays(ViewInfo::default()).is_empty());
+        if undo {
+            s.execute("edit.undo", &json!({})).unwrap();
+        } else {
+            s.execute("paint.setFill", &json!({"ids": [c.0], "color": "#ff0000"})).unwrap();
+        }
+        assert!(s.overlays(ViewInfo::default()).is_empty(), "undo {undo}: the pick is not marked");
+        let (layers, depth) = (s.doc().unwrap().doc.layers.clone(), s.doc().unwrap().history.undo.len());
+        click(&mut s, 220.0, 20.0);
+        assert_eq!(s.doc().unwrap().selection.objects, vec![b], "undo {undo}: b is picked first");
+        assert_eq!((&s.doc().unwrap().doc.layers, s.doc().unwrap().history.undo.len()), (&layers, depth), "undo {undo}: the click changes no art");
+        click(&mut s, if undo { 20.0 } else { 420.0 }, 20.0);
+        let g = s.doc().unwrap().selection.objects[0];
+        assert_eq!(spec(&s, g).0, if undo { vec![a, b] } else { vec![b, c] }, "undo {undo}");
+    }
+}
+
+#[test]
+fn removing_the_blend_the_blend_tool_adds_to_ends_adding() {
+    let mut s = session();
+    let (a, b, c) = (rect(&mut s, 0.0, 0.0, 40.0), rect(&mut s, 200.0, 0.0, 40.0), rect(&mut s, 400.0, 0.0, 40.0));
+    let (d, e) = (rect(&mut s, 0.0, 300.0, 40.0), rect(&mut s, 200.0, 300.0, 40.0));
+    let other = id_of(&s.execute("object.blend.make", &json!({"ids": [d.0, e.0]})).unwrap());
+    s.select_tool("blend", ViewInfo::default()).unwrap();
+    let click = |s: &mut Session, x: f64, y: f64| s.pointer(&PointerEvent::new(PointerKind::Down, x, y), ViewInfo::default()).unwrap();
+    click(&mut s, 20.0, 20.0);
+    click(&mut s, 220.0, 20.0);
+    let g = s.doc().unwrap().selection.objects[0];
+    s.execute("edit.clear", &json!({"ids": [g.0]})).unwrap();
+    sel(&mut s, &[other]);
+    click(&mut s, 420.0, 20.0);
+    assert_eq!(s.doc().unwrap().selection.objects, vec![c], "c is picked first");
+    assert_eq!(spec(&s, other).0, vec![d, e], "c is not added to the selected blend");
+    assert!([a, b, g].iter().all(|id| s.doc().unwrap().doc.node(*id).is_none()), "the blend went with its keys");
+}
+
+#[test]
+fn a_selection_change_keeps_the_blend_tools_first_pick() {
+    for drag in [false, true] {
+        let mut s = session();
+        let (a, b, c) = (rect(&mut s, 0.0, 0.0, 40.0), rect(&mut s, 200.0, 0.0, 40.0), rect(&mut s, 400.0, 0.0, 40.0));
+        let view = ViewInfo::default();
+        s.select_tool("blend", view).unwrap();
+        s.pointer(&PointerEvent::new(PointerKind::Down, 20.0, 20.0), view).unwrap();
+        sel(&mut s, &[c]);
+        // Cmd lends the selection tool: a click on c selects it, a drag moves it (an edit).
+        let cmd = Mods { cmd: true, ..Mods::default() };
+        let to = if drag { 440.0 } else { 420.0 };
+        s.pointer(&PointerEvent::new(PointerKind::Down, 420.0, 20.0).with_mods(cmd), view).unwrap();
+        s.pointer(&PointerEvent::new(PointerKind::Drag, to, 20.0).with_mods(cmd), view).unwrap();
+        s.pointer(&PointerEvent::new(PointerKind::Up, to, 20.0).with_mods(cmd), view).unwrap();
+        assert_eq!(s.tool_id(), "blend");
+        assert_eq!(s.overlays(view).is_empty(), drag, "drag {drag}");
+        s.pointer(&PointerEvent::new(PointerKind::Down, 220.0, 20.0), view).unwrap();
+        if drag {
+            assert_eq!(s.doc().unwrap().selection.objects, vec![b], "the drag dropped the pick");
+        } else {
+            let g = s.doc().unwrap().selection.objects[0];
+            assert_eq!(spec(&s, g).0, vec![a, b]);
+        }
+    }
+}
+
 #[test]
 fn start_points_round_trip_and_old_blends_load() {
     let mut s = session();

crates/engine/src/tooling.rs

@@ -328,6 +328,25 @@ impl Session {
         self.tool_panic.take().map_or(Ok(()), Err)
     }
 
+    /// The active document (its uid) and its [`crate::History::step`].
+    fn history_step(&self) -> Option<(u64, (u64, u64))> {
+        self.active().map(|d| (d.uid, d.history.step()))
+    }
+
+    /// Tell the active tool when the history moved, or another document became active, since it
+    /// last handled a pointer event or was last told ([`vectorcraft_tools::Tool::history_moved`]).
+    /// A lent selection tool is not told.
+    fn tell_tool_history_moved(&mut self) {
+        if self.lender.is_some() {
+            return;
+        }
+        let now = self.history_step();
+        if self.tool_step.is_some_and(|seen| Some(seen) != now) {
+            self.tool.history_moved();
+        }
+        self.tool_step = now;
+    }
+
     /// Feed a pointer event to the active tool. Returns requests for the UI.
     pub fn pointer(&mut self, ev: &PointerEvent, view: ViewInfo) -> Result<Vec<UiRequest>> {
         self.last_view = view;
@@ -341,7 +360,9 @@ impl Session {
             return r;
         }
         self.leave_draw_inside(ev, view)?;
+        self.tell_tool_history_moved();
         let ev = &self.lend_selection_tool(ev);
+        let lent = self.lender.is_some();
         let acts = self.with_tool_cx(view, |t, cx| t.pointer(cx, ev));
         let r = self.take_tool_panic().and_then(|()| {
             // A gesture may change options (Alt-drag sizes a Liquify brush): keep them.
@@ -350,6 +371,11 @@ impl Session {
             }
             self.apply_actions(acts)
         });
+        // The tool's own edits do not move the history for it. A selection tool that Cmd lends
+        // edits for the lender, which hears of the edit at its next event.
+        if !lent {
+            self.tool_step = self.history_step();
+        }
         if ev.kind == PointerKind::Up {
             self.give_back_tool(view)?;
         }
@@ -553,6 +579,8 @@ impl Session {
     }
 
     pub fn overlays(&mut self, view: ViewInfo) -> Vec<Overlay> {
+        // The Blend tool's first pick is not marked after an edit that dropped it.
+        self.tell_tool_history_moved();
         let mut v = self.with_tool_cx(view, |t, cx| t.overlays(cx));
         // The Type tools draw the ports of selected type themselves.
         if !matches!(self.tool.id(), "type" | "areaType" | "typeOnPath" | "verticalType" | "verticalAreaType" | "verticalTypeOnPath") {

crates/tools/src/lib.rs

@@ -224,6 +224,10 @@ pub trait Tool: Send {
     fn after_command(&mut self, _cx: &ToolContext) -> Vec<Action> {
         vec![]
     }
+    /// The undo history moved outside the tool (an edit, Undo or Redo the tool did not make), or
+    /// another document became active. The Blend tool drops its first pick and stops adding to the
+    /// blend it just made.
+    fn history_moved(&mut self) {}
     /// Time passes while the pointer button is held (`dt` seconds since the last tick, whether or
     /// not the pointer moved): tools that keep working while the brush holds still (Twirl, Pucker,
     /// Bloat) act on it. The host supplies the time, so tests and agents drive it exactly.

crates/tools/src/meshblend.rs

@@ -148,6 +148,11 @@ impl Tool for BlendTool {
         (self.first, self.chained) = (None, false);
         vec![]
     }
+    /// An edit, Undo or Redo made outside the tool drops the object picked first and stops adding to
+    /// the blend just made, so the next click picks a new first object.
+    fn history_moved(&mut self) {
+        (self.first, self.chained) = (None, false);
+    }
 }
 
 #[derive(Default)]