grid movement

src/snake/main.rs

@@ -1,17 +1,99 @@
-use bevy::prelude::*;
+use bevy::{prelude::*, window::PrimaryWindow};
 use bevy_inspector_egui::quick::WorldInspectorPlugin;
 
+const SNAKE_HEAD_COLOR: Color = Color::srgb(0.7, 1.0, 0.7);
+const ARENA_WIDTH: u32 = 20;
+const ARENA_HEIGHT: u32 = 15;
+const WINDOW_WIDTH: f32 = 1280.0;
+
 #[derive(Component)]
 struct SnakeHead;
 
-const SNAKE_HEAD_COLOR: Color = Color::srgb(0.7, 0.7, 0.7);
+#[derive(Component)]
+struct Position {
+    x: i32,
+    y: i32,
+}
+
+#[derive(Component)]
+struct Size {
+    width: f32,
+    height: f32,
+}
+
+impl Size {
+    pub fn square(x: f32) -> Self {
+        Self {
+            width: x,
+            height: x,
+        }
+    }
+}
+
+fn snake_movement_system(
+    input: Res<ButtonInput<KeyCode>>,
+
+    mut head_transforms: Query<(&SnakeHead, &mut Position)>,
+) {
+    for (_, mut pos) in head_transforms.iter_mut() {
+        if input.pressed(KeyCode::ArrowUp) {
+            pos.y += 1;
+        } else if input.pressed(KeyCode::ArrowDown) {
+            pos.y -= 1;
+        } else if input.pressed(KeyCode::ArrowLeft) {
+            pos.x -= 1;
+        } else if input.pressed(KeyCode::ArrowRight) {
+            pos.x += 1;
+        }
+    }
+}
+
+fn scale_translation(
+    mut windows: Query<&mut Window, With<PrimaryWindow>>,
+    mut q: Query<(&Size, &mut Transform)>,
+) {
+    let window = windows.single_mut();
+    for (sprite_size, mut transform) in q.iter_mut() {
+        transform.scale = Vec3::new(
+            sprite_size.width / ARENA_WIDTH as f32 * window.width(),
+            sprite_size.height / ARENA_HEIGHT as f32 * window.height(),
+            1.0,
+        );
+    }
+}
+
+fn position_translation(
+    mut windows: Query<&mut Window, With<PrimaryWindow>>,
+    mut q: Query<(&Position, &mut Transform)>,
+) {
+    // We subtract half the window width because our coordinate system starts at the bottom left, and
+    // Translation starts from the center. We then add half the size of a single tile, because we want
+    // our sprites bottom left corner to be at the bottom left of a tile, not the center.
+    fn convert(pos: f32, bound_window: f32, bound_game: f32) -> f32 {
+        let tile_size = bound_window / bound_game;
+        pos / bound_game * bound_window - (bound_window / 2.) + (tile_size / 2.)
+    }
+
+    let window = windows.single_mut();
+    for (pos, mut transform) in q.iter_mut() {
+        transform.translation = Vec3::new(
+            convert(pos.x as f32, window.width(), ARENA_WIDTH as f32),
+            convert(pos.y as f32, window.height(), ARENA_HEIGHT as f32),
+            0.0,
+        );
+    }
+}
 
 fn setup_player(mut commands: Commands) {
-    commands.spawn(Sprite {
+    commands
+        .spawn(Sprite {
             color: SNAKE_HEAD_COLOR,
             custom_size: Some(Vec2::new(10.0, 10.0)),
             ..default()
-    });
+        })
+        .insert(SnakeHead)
+        .insert(Position { x: 0, y: 0 })
+        .insert(Size::square(1.0));
 }
 
 fn setup_camera(mut commands: Commands) {
@@ -19,9 +101,25 @@ fn setup_camera(mut commands: Commands) {
 }
 
 fn main() {
+    let systems = snake_movement_system;
     App::new()
-        .add_plugins(DefaultPlugins)
+        .add_plugins(
+            DefaultPlugins.set(WindowPlugin {
+                primary_window: Some(Window {
+                    title: "Snake".to_string(),
+                    resolution: (
+                        WINDOW_WIDTH,
+                        WINDOW_WIDTH * (ARENA_HEIGHT as f32 / ARENA_WIDTH as f32),
+                    )
+                        .into(),
+                    ..default()
+                }),
+                ..default()
+            }),
+        )
         .add_plugins(WorldInspectorPlugin::new())
         .add_systems(Startup, (setup_camera, setup_player))
+        .add_systems(Update, systems)
+        .add_systems(PostUpdate, (scale_translation, position_translation))
         .run();
 }