feat(rapier_testbed): autosave testbed configuration + add support for per-example settings (#799)

* feat(rapier_testbed): autosave testbed configuration + add support for per-example parameters

* feat(rapier_testbed): also save the camera position

* feat(rapier_testbed): improve ergonomics of example-specific settings

* chore: cargo fmt

* chore(rapier_testbed): small UI ergonomics improvement

* chore(rapier_testbed): clippy fixes

src_testbed/save.rs

@@ -0,0 +1,34 @@
+#[cfg(feature = "dim2")]
+use crate::camera2d::OrbitCamera;
+#[cfg(feature = "dim3")]
+use crate::camera3d::OrbitCamera;
+use crate::settings::ExampleSettings;
+use crate::testbed::{RapierSolverType, RunMode, TestbedStateFlags};
+use serde::{Deserialize, Serialize};
+
+#[derive(Serialize, Deserialize, PartialEq, Debug, Default, Clone)]
+pub struct SerializableTestbedState {
+    pub running: RunMode,
+    pub flags: TestbedStateFlags,
+    pub selected_example: usize,
+    pub selected_backend: usize,
+    pub example_settings: ExampleSettings,
+    pub solver_type: RapierSolverType,
+    pub physx_use_two_friction_directions: bool,
+    pub camera: OrbitCamera,
+}
+
+#[cfg(feature = "dim2")]
+#[derive(Serialize, Deserialize, PartialEq, Debug, Default, Clone)]
+pub struct SerializableCameraState {
+    pub zoom: f32,
+    pub center: na::Point2<f32>,
+}
+
+#[cfg(feature = "dim3")]
+#[derive(Serialize, Deserialize, PartialEq, Debug, Default, Clone)]
+pub struct SerializableCameraState {
+    pub distance: f32,
+    pub position: na::Point3<f32>,
+    pub center: na::Point3<f32>,
+}