Add basic falling sand

src/falling_sand/mod.rs

@@ -11,14 +11,17 @@ use bevy::{
     sprite::SpriteBundle,
     transform::components::Transform,
 };
-use rand::random;
+use rand::Rng;
 
 pub struct FallingSandPlugin;
 
 impl Plugin for FallingSandPlugin {
     fn build(&self, app: &mut bevy::prelude::App) {
         app.add_systems(Startup, setup);
-        app.add_systems(Update, update_chunk_texture_system);
+        app.add_systems(
+            Update,
+            (simulate_chunk_system, update_chunk_texture_system).chain(),
+        );
     }
 }
 
@@ -40,10 +43,16 @@ fn setup(mut commands: Commands, mut images: ResMut<Assets<Image>>) {
         .spawn(Chunk {
             width: 256,
             height: 256,
+            cells: vec![Elements::Air; 256 * 256],
         })
         .insert(SpriteBundle {
+            sprite: Sprite {
+                flip_y: true,
+                ..default()
+            },
             texture: image_handle,
-            transform: Transform::from_translation(Vec3::new(256., 0., 0.)),
+            transform: Transform::from_translation(Vec3::new(256., 0., 0.))
+                .with_scale(Vec3::new(2., 2., 0.)),
             ..default()
         });
 }
@@ -52,6 +61,63 @@ fn setup(mut commands: Commands, mut images: ResMut<Assets<Image>>) {
 pub struct Chunk {
     width: usize,
     height: usize,
+    cells: Vec<Elements>,
+}
+
+pub fn simulate_chunk_system(mut chunk: Query<&mut Chunk>) {
+    // We know for now there's only one chunk
+    let chunk = chunk.get_single_mut();
+    if chunk.is_err() {
+        return;
+    }
+
+    let mut query = chunk.unwrap();
+    let chunk = query.as_mut();
+
+    // Place sand
+    let frac = chunk.width / 2;
+    let x = (chunk.width - frac) / 2 + rand::thread_rng().gen_range(0..frac);
+    let y = chunk.height - 1;
+    chunk.cells[x + y * chunk.width] = Elements::Sand;
+
+    // Simulate sand
+    for y in 0..chunk.height {
+        for x in 0..chunk.width {
+            let index = x + y * chunk.width;
+            let element = chunk.cells.get(index).unwrap();
+            match element {
+                Elements::Air => {}
+                Elements::Sand => {
+                    if y != 0 {
+                        let b_index = index - chunk.width;
+                        let bottom = chunk.cells.get(b_index).unwrap();
+                        if *bottom == Elements::Air {
+                            chunk.cells.swap(index, b_index);
+                            continue;
+                        }
+
+                        if x != 0 {
+                            let bl_index = b_index - 1;
+                            let bottom_left = chunk.cells.get(bl_index).unwrap();
+                            if *bottom_left == Elements::Air {
+                                chunk.cells.swap(index, bl_index);
+                                continue;
+                            }
+                        }
+
+                        if x != chunk.width - 1 {
+                            let br_index = b_index + 1;
+                            let bottom_right = chunk.cells.get(br_index).unwrap();
+                            if *bottom_right == Elements::Air {
+                                chunk.cells.swap(index, br_index);
+                                continue;
+                            }
+                        }
+                    }
+                }
+            }
+        }
+    }
 }
 
 pub fn update_chunk_texture_system(
@@ -68,13 +134,26 @@ pub fn update_chunk_texture_system(
     if let Some(image) = images.get_mut(image_handle) {
         for y in 0..chunk.height {
             for x in 0..chunk.width {
-                // Just set each pixel to random colours for now
+                let mut colour = (0, 0, 0);
+                if let Some(element) = chunk.cells.get(x + y * chunk.width) {
+                    match element {
+                        Elements::Air => colour = (25, 24, 26),
+                        Elements::Sand => colour = (255, 216, 102),
+                    }
+                }
+
                 let index = (x + y * chunk.width) * 4;
-                image.data[index] = random::<u8>();
-                image.data[index + 1] = random::<u8>();
-                image.data[index + 2] = random::<u8>();
+                image.data[index] = colour.0;
+                image.data[index + 1] = colour.1;
+                image.data[index + 2] = colour.2;
                 image.data[index + 3] = 255;
             }
         }
     }
 }
+
+#[derive(Debug, Clone, Copy, PartialEq)]
+enum Elements {
+    Air,
+    Sand,
+}