From cdbac0d4ab03a5fe2bf243993118bb09e7d74834 Mon Sep 17 00:00:00 2001
From: reo <emre@reoco.de>
Date: Mon, 30 Jun 2025 23:29:41 +0300
Subject: [PATCH] Improve ECS

Use query_one_mut instead of query_mut for single objects
---
 src/ecs.rs    | 13 -------------
 src/main.rs   | 19 ++++++++++++-------
 src/render.rs |  1 -
 3 files changed, 12 insertions(+), 21 deletions(-)

diff --git a/src/ecs.rs b/src/ecs.rs
index 2fed082..0f47217 100644
--- a/src/ecs.rs
+++ b/src/ecs.rs
@@ -17,16 +17,3 @@ impl Transform {
 #[derive(Clone)]
 pub struct MeshHandle(pub usize);
 
-/// ------------ systems ------------
-pub fn rotation_system(world: &mut World, dt: f32) {
-    for (_, transform) in world.query_mut::<&mut Transform>() {
-        transform.rotation *= Quat::from_rotation_y(dt);
-    }
-}
-
-/// Update the aspect ratio for all camera components in the world.
-pub fn set_camera_aspect(world: &mut World, aspect: f32) {
-    for (_, cam) in world.query_mut::<&mut crate::camera::Camera>() {
-        cam.aspect = aspect;
-    }
-}
diff --git a/src/main.rs b/src/main.rs
index 7d0ac14..cebe8e7 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -5,7 +5,7 @@ mod render;
 
 use anyhow::Result;
 use camera::Camera;
-use ecs::{rotation_system, MeshHandle, Transform};
+use ecs::{MeshHandle, Transform};
 use glam::{Quat, Vec3};
 use glium::backend::glutin::SimpleWindowBuilder;
 use render::{Renderer, GliumRenderer};
@@ -29,7 +29,7 @@ fn main() -> Result<()> {
     let mesh_id      = renderer.meshes.len();
     renderer.meshes.push(mesh);
 
-    world.spawn((
+    let object_ent = world.spawn((
         Transform {
             translation: Vec3::ZERO,
             rotation:    Quat::IDENTITY,
@@ -38,7 +38,8 @@ fn main() -> Result<()> {
         MeshHandle(mesh_id),
     ));
 
-    {
+
+    let camera_ent = {
         let (w, h): (u32, u32) = window.inner_size().into();
         world.spawn((Camera {
             eye:    Vec3::new(3.0, 2.0, 3.0),
@@ -48,8 +49,8 @@ fn main() -> Result<()> {
             aspect: w as f32 / h as f32,
             znear:  0.1,
             zfar:   100.0,
-        },));
-    }
+        },))
+    };
 
     event_loop
         .run(move |event, el| {
@@ -59,7 +60,9 @@ fn main() -> Result<()> {
                 Event::WindowEvent { event, .. } => match event {
                     WindowEvent::CloseRequested => el.exit(),
                     WindowEvent::Resized(sz) => {
-                        ecs::set_camera_aspect(&mut world, sz.width as f32 / sz.height as f32);
+                        world.query_one_mut::<&mut crate::camera::Camera>(camera_ent).map(|mut cam| {
+                            cam.aspect = sz.width as f32 / sz.height as f32;
+                        });
                     }
                     WindowEvent::RedrawRequested => {
                         renderer.render(&world);
@@ -74,7 +77,9 @@ fn main() -> Result<()> {
                         let last = LAST.replace(now).unwrap_or(now);
                         (now - last).as_secs_f32()
                     };
-                    rotation_system(&mut world, dt);
+                    world.query_one_mut::<&mut Transform>(object_ent).map(|mut object| {
+                        object.rotation *= Quat::from_rotation_y(dt);
+                    });
 
                     // ask for next frame
                     window.request_redraw();
diff --git a/src/render.rs b/src/render.rs
index 3f579c0..a4097db 100644
--- a/src/render.rs
+++ b/src/render.rs
@@ -72,7 +72,6 @@ impl Renderer for GliumRenderer {
         let mut frame = self.display.draw();
         frame.clear_color_and_depth((0.1, 0.1, 0.15, 1.0), 1.0);
 
-        // Expect exactly one active camera in the world.
         let cam = match world.query::<&Camera>().iter().next() {
             Some((_, cam)) => *cam,
             None => {