Show which is the up-axis when showing orbit center

crates/re_space_view_spatial/src/ui_3d.rs

@@ -680,17 +680,45 @@ pub fn view_3d(
 
         if orbit_center_fade > 0.001 {
             let half_line_length = orbit_eye.orbit_radius * 0.03;
-
             let half_line_length = half_line_length * orbit_center_fade;
 
+            // We distinguish the eye up-axis from the other two axes:
+
+            // Default to RFU
+            let up = if orbit_eye.eye_up == Vec3::ZERO {
+                glam::Vec3::Z
+            } else {
+                orbit_eye.eye_up.normalize()
+            };
+            let (right, forward) = up.any_orthonormal_pair();
+            // let right = scene_view_coordinates
+            //     .and_then(|vc| vc.right())
+            //     .map(Vec3::from)
+            //     .unwrap_or(glam::Vec3::X);
+            // let forward = scene_view_coordinates
+            //     .and_then(|vc| vc.forward())
+            //     .map(Vec3::from)
+            //     .unwrap_or(glam::Vec3::Y);
+
             line_builder
                 .batch("center orbit orientation help")
-                .add_segments(glam::Vec3::AXES.iter().map(|axis| {
-                    (
-                        orbit_eye.orbit_center - *axis * half_line_length,
-                        orbit_eye.orbit_center + *axis * half_line_length,
-                    )
-                }))
+                .add_segments(
+                    [
+                        (
+                            orbit_eye.orbit_center,
+                            orbit_eye.orbit_center + 0.5 * up * half_line_length,
+                        ),
+                        (
+                            orbit_eye.orbit_center - right * half_line_length,
+                            orbit_eye.orbit_center + right * half_line_length,
+                        ),
+                        (
+                            orbit_eye.orbit_center - forward * half_line_length,
+                            orbit_eye.orbit_center + forward * half_line_length,
+                        ),
+                    ]
+                    .into_iter(),
+                )
                 .radius(Size::new_points(0.75))
                 // TODO(andreas): Fade this out.
                 .color(re_renderer::Color32::WHITE);