feat(ellipse): add complete grip editing

src/scene/model/object.rs

@@ -101,10 +101,8 @@ pub struct GripDef {
     pub is_midpoint: bool,
     /// Visual marker shape for the grip.
     pub shape: GripShape,
-    /// World-XY direction vector used to orient a `Rectangle` grip
-    /// along its segment. `None` for shapes that don't need rotation
-    /// (Square, Triangle in non-directional contexts).
-    pub dir: Option<[f32; 2]>,
+    /// World-space marker direction, projected with the grip position.
+    pub dir: Option<glam::DVec3>,
     /// World-space axis that constrains this grip's drag.
     pub axis: Option<glam::DVec3>,
 }

src/scene/pick/grip.rs

@@ -78,6 +78,10 @@ impl GripEdit {
 
 // ── Screen-space helpers ───────────────────────────────────────────────────
 
+fn marker_direction(from: Vec2, to: Vec2) -> [f32; 2] {
+    [to.x - from.x, from.y - to.y]
+}
+
 /// Project a slice of `GripDef`s to screen space.
 /// Returns `(grip_id, screen_pos, is_midpoint, shape)` for each grip.
 pub fn grips_to_screen(
@@ -91,11 +95,18 @@ pub fn grips_to_screen(
             // Project from the f64 grip position via the relative-to-eye path so
             // the grip stays glued to the wire at UTM-scale coordinates (an
             // `as_vec3` cast first would quantize it ~0.5 m off at high zoom).
-            let screen = match camera.project(g.world, bounds) {
+            let projected = camera.project(g.world, bounds);
+            let screen = match projected {
                 Some(p) => Point::new(bounds.x + p.x, bounds.y + p.y),
                 None => Point::new(f32::NAN, f32::NAN),
             };
-            (g.id, screen, g.is_midpoint, g.shape, g.dir)
+            let dir = g.dir.and_then(|dir| {
+                Some(marker_direction(
+                    projected?,
+                    camera.project(g.world + dir, bounds)?,
+                ))
+            });
+            (g.id, screen, g.is_midpoint, g.shape, dir)
         })
         .collect()
 }
@@ -110,14 +121,24 @@ pub fn grips_to_screen_paper(
     half_h: f32,
     bounds: Rectangle,
 ) -> Vec<(usize, Point, bool, GripShape, Option<[f32; 2]>)> {
+    let project = |world: DVec3| {
+        Vec2::new(
+            (world.x as f32 - tx + half_w) / (2.0 * half_w) * bounds.width,
+            (ty + half_h - world.y as f32) / (2.0 * half_h) * bounds.height,
+        )
+    };
     grips
         .iter()
         .map(|g| {
-            let screen = Point::new(
-                (g.world.x as f32 - tx + half_w) / (2.0 * half_w) * bounds.width,
-                (ty + half_h - g.world.y as f32) / (2.0 * half_h) * bounds.height,
-            );
-            (g.id, screen, g.is_midpoint, g.shape, g.dir)
+            let projected = project(g.world);
+            let screen = Point::new(projected.x, projected.y);
+            let dir = g.dir.map(|dir| {
+                [
+                    dir.x as f32 / (2.0 * half_w) * bounds.width,
+                    dir.y as f32 / (2.0 * half_h) * bounds.height,
+                ]
+            });
+            (g.id, screen, g.is_midpoint, g.shape, dir)
         })
         .collect()
 }
@@ -207,11 +228,18 @@ pub fn grips_to_screen_rte(
     grips
         .iter()
         .map(|g| {
-            let screen = match project_rte(g.world, view_rot, eye, bounds) {
+            let projected = project_rte(g.world, view_rot, eye, bounds);
+            let screen = match projected {
                 Some(p) => Point::new(bounds.x + p.x, bounds.y + p.y),
                 None => Point::new(f32::NAN, f32::NAN),
             };
-            (g.id, screen, g.is_midpoint, g.shape, g.dir)
+            let dir = g.dir.and_then(|dir| {
+                Some(marker_direction(
+                    projected?,
+                    project_rte(g.world + dir, view_rot, eye, bounds)?,
+                ))
+            });
+            (g.id, screen, g.is_midpoint, g.shape, dir)
         })
         .collect()
 }