From b8a626194bf886c67eb5bd9114179efed3f3f3fd Mon Sep 17 00:00:00 2001
From: Elijah Voigt <elijah.caine.mv@gmail.com>
Date: Mon, 18 Aug 2025 11:34:39 -0700
Subject: [PATCH] Slight rework of parallax system

---
 examples/parallax.rs | 35 +++++++++++--------------
 src/parallax.rs      | 62 +++++++++++++++++++++++---------------------
 2 files changed, 47 insertions(+), 50 deletions(-)

diff --git a/examples/parallax.rs b/examples/parallax.rs
index f12c8bd..f302a9e 100644
--- a/examples/parallax.rs
+++ b/examples/parallax.rs
@@ -10,7 +10,6 @@ fn main() {
         .add_systems(Startup, spawn_background)
         .add_systems(Update, move_camera)
         .add_systems(Update, parallax_gizmos)
-        .add_systems(Update, move_parallax_items)
         .run();
 }
 
@@ -19,33 +18,42 @@ fn spawn_background(
     mut meshes: ResMut<Assets<Mesh>>,
     mut materials: ResMut<Assets<ColorMaterial>>,
 ) {
-    let mesh = Mesh2d(meshes.add(Circle::new(50.0)));
+    let mesh = Mesh2d(meshes.add(Circle::new(1.0)));
     let material = MeshMaterial2d(materials.add(ColorMaterial::from_color(RED)));
+    let transform = Transform::default().with_scale(Vec3::splat(50.0));
     commands.spawn((
+        Name::new("Depth: 1"),
+        transform,
         mesh.clone(),
         material.clone(),
-        Parallax(1.0),
+        ParallaxDepth(1.0),
         Visibility::Inherited,
         children![(Text2d("1.0".into()), Transform::from_xyz(0.0, 35.0, 0.0))],
     ));
     commands.spawn((
+        Name::new("Depth: 2"),
+        transform,
         mesh.clone(),
         material.clone(),
-        Parallax(2.0),
+        ParallaxDepth(2.0),
         Visibility::Inherited,
         children![(Text2d("2.0".into()), Transform::from_xyz(0.0, 35.0, 0.0))],
     ));
     commands.spawn((
+        Name::new("Depth: 4"),
+        transform,
         mesh.clone(),
         material.clone(),
-        Parallax(4.0),
+        ParallaxDepth(4.0),
         Visibility::Inherited,
         children![(Text2d("4.0".into()), Transform::from_xyz(0.0, 35.0, 0.0))],
     ));
     commands.spawn((
+        Name::new("Depth: 8"),
+        transform,
         mesh.clone(),
         material.clone(),
-        Parallax(8.0),
+        ParallaxDepth(8.0),
         Visibility::Inherited,
         children![(Text2d("8.0".into()), Transform::from_xyz(0.0, 35.0, 0.0))],
     ));
@@ -65,7 +73,7 @@ fn move_camera(mut t: Single<&mut Transform, With<Camera2d>>, keys: Res<ButtonIn
     }
 }
 
-fn parallax_gizmos(mut gizmos: Gizmos, q: Query<&Transform, With<Parallax>>) {
+fn parallax_gizmos(mut gizmos: Gizmos, q: Query<&Transform, With<ParallaxDepth>>) {
     // Closest to camera
     // Parallax(1)
     q.iter().for_each(|t| {
@@ -79,16 +87,3 @@ fn parallax_gizmos(mut gizmos: Gizmos, q: Query<&Transform, With<Parallax>>) {
             .outer_edges();
     });
 }
-
-// TODO: Move to src/parallax.rs
-fn move_parallax_items(
-    mut q: Query<(Entity, &ViewVisibility, &mut ParallaxRepeatIteration), (With<Parallax>, Changed<ViewVisibility>)>,
-) {
-    q.iter_mut().for_each(|(e, vis, mut pri)| {
-        warn!("{e} {:?}", vis.get());
-        if !vis.get() {
-            pri.0 += 1;
-            todo!("Works when moving camera right, make it work left too");
-        }
-    });
-}
diff --git a/src/parallax.rs b/src/parallax.rs
index 232b246..ad799c4 100644
--- a/src/parallax.rs
+++ b/src/parallax.rs
@@ -11,40 +11,42 @@ impl Plugin for ParallaxPlugin {
     }
 }
 
+///
+/// ParallaxDepth describes how far from the camera something is
+///
+/// A parallax depth of 1 means it moves 1:1 with camera movement;
+/// If the camera moves 1 pixel to the left, the background moves 1px to the right
+///
+/// A parallax depth of 2 means the movement is 1:2
+/// Camera moves 2px, the element moves 1px
+///
 #[derive(Component)]
-#[require(Transform, ParallaxRepeat, ParallaxRepeatIteration)]
-pub struct Parallax(pub f32);
-
-#[derive(Component)]
-pub struct ParallaxRepeat(pub f32);
-
-impl Default for ParallaxRepeat{
-    fn default() -> Self {
-        ParallaxRepeat(1.0)
-    }
-}
-
-#[derive(Component, Default)]
-pub struct ParallaxRepeatIteration(pub isize);
+pub struct ParallaxDepth(pub f32);
 
 fn move_parallax_items(
-    mut q: Query<(&mut Transform, &Parallax, &ParallaxRepeat, &ParallaxRepeatIteration), Without<Camera2d>>,
-    camera: Single<(&Camera, &Transform, &GlobalTransform), With<Camera2d>>,
-    window: Single<&Window>
+    mut q: Query<(&mut Transform, &ParallaxDepth), Without<Camera>>,
+    window: Single<&Window>,
+    camera: Single<(&Camera, &Transform, &GlobalTransform), (With<Camera2d>, Changed<Transform>)>,
+    mut prev_camera_pos: Local<Vec2>,
 ) {
+    // Unpack the camera data
     let (cam, cam_t, cam_gt) = *camera;
-    let base = cam_t.translation.truncate();
-    let size = window.size();
-
-    q.iter_mut().for_each(|(mut t, p, pr, pri)| {
-        let offset: Vec2 = {
-            let a = cam.viewport_to_world_2d(cam_gt, Vec2::new(0.0, size.y / 2.0)).unwrap();
-            let b = cam.viewport_to_world_2d(cam_gt, Vec2::new(size.x, size.y / 2.0)).unwrap();
-            (b - a) * pr.0 * (pri.0 as f32)
-        };
-        // Something like add screen-dimensions * parallax repeat cycle number
-        let val = base * (1.0 - (1.0 / p.0)) + offset;
-        t.translation.x = val.x;
-        t.translation.y = val.y;
+
+    // Calculate how far the camera moved since the last update
+    let delta = cam_t.translation.truncate() - *prev_camera_pos;
+    debug!("Cam Delta: {:?}", delta);
+
+    // For each object
+    q.iter_mut().for_each(|(mut t, pd)| {
+        // Update ParallaxPosition
+        let depth_movement = delta / pd.0;
+
+        debug!("Depth: {:?} | Move: {:?}", pd.0, depth_movement);
+
+        // Update actual position
+        t.translation.x -= depth_movement.x;
+        t.translation.y -= depth_movement.y;
     });
+
+    *prev_camera_pos = cam_t.translation.truncate();
 }