From 1f534bb1aacbe0a30b7fadc145e3a09e1703a667 Mon Sep 17 00:00:00 2001
From: SeanOMik <seanomik@gmail.com>
Date: Thu, 26 Oct 2023 12:17:10 -0400
Subject: [PATCH] Fix unintended roll of fly cam

---
 examples/testbed/src/free_fly_camera.rs | 18 ++++++++++++------
 1 file changed, 12 insertions(+), 6 deletions(-)

diff --git a/examples/testbed/src/free_fly_camera.rs b/examples/testbed/src/free_fly_camera.rs
index 590c850..10cdb45 100644
--- a/examples/testbed/src/free_fly_camera.rs
+++ b/examples/testbed/src/free_fly_camera.rs
@@ -5,7 +5,7 @@ use lyra_engine::{
     ecs::{components::camera::CameraComponent, EventQueue, SimpleSystem},
     game::Game,
     input::{InputButtons, KeyCode, MouseMotion},
-    math::{Angle, Quat, Vec3},
+    math::{Angle, Quat, Vec3, EulerRot},
     plugin::Plugin,
 };
 use tracing::debug;
@@ -23,7 +23,7 @@ impl Default for FreeFlyCamera {
         Self {
             speed: 0.07,
             look_speed: 0.01,
-            mouse_sensitivity: 0.03,
+            mouse_sensitivity: 0.04,
             look_with_keys: false,
         }
     }
@@ -86,7 +86,7 @@ impl SimpleSystem for FreeFlyCameraController {
         {
             let forward = cam.transform.forward();
             let left = cam.transform.left();
-            let up = cam.transform.up();
+            let up = Vec3::Y;
 
             // handle camera movement
             if let Some(keys) = keys.as_ref() {
@@ -130,9 +130,15 @@ impl SimpleSystem for FreeFlyCameraController {
 
             if camera_rot != Vec3::ZERO {
                 let look_velocity = camera_rot * fly.look_speed;
-                cam.transform.rotation *= Quat::from_rotation_x(look_velocity.x)
-                    * Quat::from_rotation_y(look_velocity.y)
-                    * Quat::from_rotation_z(look_velocity.z);
+
+                let (mut y, mut x, _) = cam.transform.rotation.to_euler(EulerRot::YXZ);
+                x += look_velocity.x;
+                y += look_velocity.y;
+                x = x.clamp(-1.54, 1.54);
+
+                // rotation is not commutative, keep this order to avoid unintended roll
+                cam.transform.rotation = Quat::from_axis_angle(Vec3::Y, y)
+                    * Quat::from_axis_angle(Vec3::X, x);
             }
         }