Fix forever repaint of big scenes (#5071)

### What
* Closes #5018

When first loading a scene, before the user interacts, we want to center
the eye-camera on the scene, so each frame we call "interpolate to the
default eye". This should be fine, because we have an early-out if we're
already at target. However, the interpolation code had a rounding error
meaning we reached _very close_ to our goal, but not quite there. In
particular, in `arkit_scenes` it would lead to a forever repaint, since
the eye-camera would never reach its target, and so thus would require
more animation.

This manifested in `arkit_scenes` now due to another bug
(#5070) causing enormous point
clouds, making the rounding errors larger than usual.

### Checklist
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the [Code of
Conduct](https://github.com/rerun-io/rerun/blob/main/CODE_OF_CONDUCT.md)
* [x] I've included a screenshot or gif (if applicable)
* [x] I have tested the web demo (if applicable):
* Using newly built examples:
[app.rerun.io](https://app.rerun.io/pr/5071/index.html)
* Using examples from latest `main` build:
[app.rerun.io](https://app.rerun.io/pr/5071/index.html?manifest_url=https://app.rerun.io/version/main/examples_manifest.json)
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[app.rerun.io](https://app.rerun.io/pr/5071/index.html?manifest_url=https://app.rerun.io/version/nightly/examples_manifest.json)
* [x] The PR title and labels are set such as to maximize their
usefulness for the next release's CHANGELOG
* [x] If applicable, add a new check to the [release
checklist](tests/python/release_checklist)!

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crates/re_space_view_spatial/src/eye.rs

@@ -209,13 +209,19 @@ impl OrbitEye {
     }
 
     pub fn lerp(&self, other: &Self, t: f32) -> Self {
-        Self {
-            orbit_center: self.orbit_center.lerp(other.orbit_center, t),
-            orbit_radius: lerp(self.orbit_radius..=other.orbit_radius, t),
-            world_from_view_rot: self.world_from_view_rot.slerp(other.world_from_view_rot, t),
-            fov_y: egui::lerp(self.fov_y..=other.fov_y, t),
-            up: self.up.lerp(other.up, t).normalize_or_zero(),
-            velocity: self.velocity.lerp(other.velocity, t),
+        if t == 0.0 {
+            *self // avoid rounding errors
+        } else if t == 1.0 {
+            *other // avoid rounding errors
+        } else {
+            Self {
+                orbit_center: self.orbit_center.lerp(other.orbit_center, t),
+                orbit_radius: lerp(self.orbit_radius..=other.orbit_radius, t),
+                world_from_view_rot: self.world_from_view_rot.slerp(other.world_from_view_rot, t),
+                fov_y: egui::lerp(self.fov_y..=other.fov_y, t),
+                up: self.up.lerp(other.up, t).normalize_or_zero(),
+                velocity: self.velocity.lerp(other.velocity, t),
+            }
         }
     }
 

crates/re_space_view_spatial/src/ui_3d.rs

@@ -147,10 +147,6 @@ impl View3DState {
             let t = t.clamp(0.0, 1.0);
             let t = ease_out(t);
 
-            if t < 1.0 {
-                response.ctx.request_repaint();
-            }
-
             if let Some(target_orbit) = &cam_interpolation.target_orbit {
                 *orbit_eye = cam_interpolation.start.lerp(target_orbit, t);
             } else if let Some(target_eye) = &cam_interpolation.target_eye {
@@ -160,12 +156,12 @@ impl View3DState {
                 self.eye_interpolation = None;
             }
 
-            if 1.0 <= t {
-                // We have arrived at our target
-                self.eye_interpolation = None;
-            } else {
+            if t < 1.0 {
                 // There's more frames to render to finish interpolation.
                 response.ctx.request_repaint();
+            } else {
+                // We have arrived at our target
+                self.eye_interpolation = None;
             }
         }
 
@@ -256,6 +252,10 @@ impl View3DState {
         // the user wants to move the camera somewhere, so stop spinning
         self.spin = false;
 
+        if self.orbit_eye == Some(target) {
+            return; // We're already there.
+        }
+
         // Don't restart interpolation if we're already on it.
         if let Some(eye_interpolation) = &self.eye_interpolation {
             if eye_interpolation.target_orbit == Some(target) {
@@ -329,7 +329,8 @@ impl EyeInterpolation {
             .angle_between(stop.world_from_rub_view.rotation());
 
         // Threshold to avoid doing pointless interpolations that trigger frame requests.
-        if angle_difference < 0.01 && start.pos_in_world().distance(stop.pos_in_world()) < 0.0001 {
+        let distance = start.pos_in_world().distance(stop.pos_in_world());
+        if angle_difference < 0.01 && distance < 0.0001 {
             None
         } else {
             Some(egui::remap_clamp(