G1: Pin grid dialog bounds to canvas click via reference locator (#1377)

Store the click as __anchorX/__anchorY and recompute x/y when the locator opens or changes so the chosen point stays on the click like Illustrator.

Co-authored-by: Cursor <cursoragent@cursor.com>

crates/ui-egui/src/dialogs/shapes.rs

@@ -2,7 +2,7 @@
 //! Star, Line Segment Tool Options and the two grids (size, divider counts and skews, switches).
 
 use serde_json::{Value, json};
-use vectorcraft_geom::Rect;
+use vectorcraft_geom::{Point, Rect};
 
 use super::{DialogSpec, form, run_and_close};
 use crate::panels::transform::artboard_rect;
@@ -48,6 +48,16 @@ fn set_grid_placed(d: &mut Dialog, r: Rect) {
     d.fields.insert("height".into(), json!(r.height()));
 }
 
+/// Top-left `x`/`y` so reference point `refi` sits on the canvas click (`__anchorX`/`__anchorY`).
+pub(crate) fn grid_pin_to_anchor(d: &mut Dialog) {
+    let anchor = Point::new(d.f64("__anchorX", d.f64("x", 0.0)), d.f64("__anchorY", d.f64("y", 0.0)));
+    let refi = grid_reference(d);
+    let (w, h) = (d.f64("width", 100.0), d.f64("height", 100.0));
+    let rp = vectorcraft_geom::reference_point(Rect::new(0.0, 0.0, w, h), refi);
+    d.fields.insert("x".into(), json!(anchor.x - rp.x));
+    d.fields.insert("y".into(), json!(anchor.y - rp.y));
+}
+
 /// The form's fields, then a grid's switches.
 fn body(app: &mut VectorcraftApp, ui: &mut egui::Ui, d: &mut Dialog) -> bool {
     let unit = app.session.general_unit();
@@ -56,6 +66,7 @@ fn body(app: &mut VectorcraftApp, ui: &mut egui::Ui, d: &mut Dialog) -> bool {
             let refi = grid_reference(d);
             if let Some(i) = widgets::reference_point(ui, refi) {
                 d.fields.insert("reference".into(), json!(i));
+                grid_pin_to_anchor(d);
             }
         });
         ui.add_space(4.0);

crates/ui-egui/src/dialogs/tests_rectangular_grid.rs

@@ -159,6 +159,17 @@ fn key_frame(app: &mut VectorcraftApp, key: egui::Key) {
     out.textures_delta.clear();
 }
 
+#[test]
+fn rectangular_grid_reference_locator_reanchors_to_the_click() {
+    let mut app = app();
+    click(&mut app, Point::new(100.0, 100.0));
+    set(&mut app, "reference", json!(4));
+    super::shapes::grid_pin_to_anchor(app.ui.dialog.as_mut().unwrap());
+    assert_eq!((field(&app, "x"), field(&app, "y")), (json!(50.0), json!(50.0)));
+    let id = confirm(&mut app);
+    assert_grid(&app, id, Rect::new(50.0, 50.0, 150.0, 150.0), 5, 5);
+}
+
 /// #1377: OK uses the bounding box after a reference-point resize (`artboard_rect` keeps the
 /// center pinned when width doubles).
 #[test]

crates/ui-egui/src/dialogs/tools.rs

@@ -3,6 +3,7 @@
 
 use serde_json::{Value, json};
 
+use super::shapes::grid_pin_to_anchor;
 use crate::VectorcraftApp;
 use crate::state::Dialog;
 
@@ -18,17 +19,17 @@ pub fn open_tool_dialog(app: &mut VectorcraftApp, kind: &str, p: Value) {
         "lineSegment" => Dialog::new(kind, json!({"x": x, "y": y, "length": "100 pt", "angle": 0})),
         // The grids: the tool's stored options (divider counts and skews, switches) at the default size.
         "rectangularGrid" | "polarGrid" => {
-            let mut fields = app.session.tool_options_of(kind);
-            for (key, value) in [
-                ("x", json!(x)),
-                ("y", json!(y)),
-                ("width", json!("100 pt")),
-                ("height", json!("100 pt")),
-                ("reference", json!(0)),
-            ] {
-                fields[key] = value;
+            let mut obj = match app.session.tool_options_of(kind) {
+                Value::Object(o) => o,
+                _ => serde_json::Map::new(),
+            };
+            for (key, value) in [("__anchorX", json!(x)), ("__anchorY", json!(y)), ("width", json!("100 pt")), ("height", json!("100 pt"))] {
+                obj.insert(key.into(), value);
             }
-            Dialog::new(kind, fields)
+            obj.insert("reference".into(), json!(0));
+            let mut d = Dialog::new(kind, Value::Object(obj));
+            grid_pin_to_anchor(&mut d);
+            d
         }
         // Graph tool click: the graph's size.
         "graph" => Dialog::new(