Merge branch 'feat/gas-dispersion'

Cargo.lock

@@ -2084,6 +2084,7 @@ dependencies = [
  "bevy-inspector-egui",
  "bevy_prototype_debug_lines",
  "bevy_rapier2d",
+ "fastrand",
  "lazy_static",
  "noise",
 ]

Cargo.toml

@@ -10,6 +10,7 @@ bevy = { version = "0.9.0", features = ["dynamic"] }
 bevy-inspector-egui = "0.14.0"
 bevy_prototype_debug_lines = "0.9.0"
 bevy_rapier2d = "0.19.0"
+fastrand = "1.8.0"
 lazy_static = "1.4.0"
 noise = "0.8.2"
 

src/game.rs

@@ -7,10 +7,7 @@ use crate::{
 };
 
 use self::{
-    camera::{GameCameraPlugin, WORLD_WIDTH},
-    debug::DebugPlugin,
-    kinematic::KinematicPlugin,
-    player::PlayerPlugin,
+    camera::GameCameraPlugin, debug::DebugPlugin, kinematic::KinematicPlugin, player::PlayerPlugin,
 };
 
 pub mod camera;
@@ -35,15 +32,15 @@ pub fn init() {
 
 fn setup_window(mut windows: ResMut<Windows>) {
     if let Some(window) = windows.get_primary_mut() {
-        window.set_resolution(900.0, 450.0);
+        window.set_resolution(1280.0, 720.0);
         window.set_title("Kuilu".to_string());
     }
 }
 
 fn setup_terrain(mut commands: Commands, mut terrain: ResMut<Terrain2D>) {
     let terrain_gen = TerrainGen2D::new(432678);
-    for y in 0..(WORLD_WIDTH / Chunk2D::SIZE_Y as i32) {
-        for x in 0..(WORLD_WIDTH / Chunk2D::SIZE_X as i32) {
+    for y in 0..(Terrain2D::WORLD_HEIGHT / Chunk2D::SIZE_Y as i32) {
+        for x in 0..(Terrain2D::WORLD_WIDTH / Chunk2D::SIZE_X as i32) {
             let position = Vector2I { x, y };
             terrain.add_chunk(position, terrain_gen.gen_chunk(&position));
         }
@@ -60,6 +57,6 @@ fn setup_terrain(mut commands: Commands, mut terrain: ResMut<Terrain2D>) {
         .spawn(Name::new("Right wall"))
         .insert(Collider::halfspace(Vec2::NEG_X).unwrap())
         .insert(TransformBundle::from_transform(
-            Transform::from_translation(Vec3::new(WORLD_WIDTH as f32, 0.0, 0.0)),
+            Transform::from_translation(Vec3::new(Terrain2D::WORLD_WIDTH as f32, 0.0, 0.0)),
         ));
 }

src/game/camera.rs

@@ -4,9 +4,10 @@ use bevy::{
 };
 use bevy_inspector_egui::{Inspectable, RegisterInspectable};
 
-use crate::util::{move_towards_vec3, vec3_lerp};
-
-pub const WORLD_WIDTH: i32 = 512;
+use crate::{
+    terrain2d::Terrain2D,
+    util::{move_towards_vec3, vec3_lerp},
+};
 
 pub struct GameCameraPlugin;
 
@@ -48,7 +49,7 @@ fn camera_setup(mut commands: Commands) {
         Name::new("Camera"),
         Camera2dBundle {
             projection: OrthographicProjection {
-                scaling_mode: ScalingMode::FixedHorizontal(WORLD_WIDTH as f32),
+                scaling_mode: ScalingMode::FixedHorizontal(Terrain2D::WORLD_WIDTH as f32),
                 window_origin: WindowOrigin::Center,
                 scale: 1.0 / 2.0,
                 ..default()
@@ -79,7 +80,7 @@ fn camera_system(
 
     for (mut camera_transform, projection) in camera_query.iter_mut() {
         let left_limit = 0.0;
-        let right_limit = WORLD_WIDTH as f32;
+        let right_limit = Terrain2D::WORLD_WIDTH as f32;
         let offset = Vec3::new(0.0, 0.0, 999.9);
         match follow.movement {
             FollowMovement::Instant => {

src/game/debug.rs

@@ -1,9 +1,7 @@
 use bevy::prelude::*;
-// use bevy_inspector_egui::*;
 use bevy_prototype_debug_lines::DebugLinesPlugin;
-// use bevy_rapier2d::prelude::*;
 
-mod terrain;
+pub mod terrain;
 
 use terrain::TerrainDebugPlugin;
 
@@ -12,8 +10,8 @@ pub struct DebugPlugin;
 impl Plugin for DebugPlugin {
     fn build(&self, app: &mut App) {
         app.add_plugin(DebugLinesPlugin::default())
-            // .add_plugin(RapierDebugRenderPlugin::default())
-            // .add_plugin(WorldInspectorPlugin::new())
+            // .add_plugin(bevy_rapier2d::prelude::RapierDebugRenderPlugin::default())
+            // .add_plugin(bevy_inspector_egui::WorldInspectorPlugin::new())
             .add_plugin(TerrainDebugPlugin);
     }
 }

src/game/debug/terrain.rs

@@ -1,3 +1,5 @@
+use std::collections::HashMap;
+
 use crate::{game::camera::GameCamera, terrain2d::*, util::Vector2I};
 use bevy::{input::mouse::MouseWheel, prelude::*, render::camera::RenderTarget};
 use bevy_prototype_debug_lines::DebugLines;
@@ -7,7 +9,8 @@ pub struct TerrainDebugPlugin;
 impl Plugin for TerrainDebugPlugin {
     fn build(&self, app: &mut App) {
         app.insert_resource(TerrainBrush2D::default())
-            .add_system_to_stage(TerrainStages::EventHandler, dirty_rect_visualizer)
+            // .add_system_to_stage(TerrainStages::EventHandler, dirty_rect_visualizer)
+            // .add_system_to_stage(CoreStage::Last, chunk_debugger)
             .add_system(debug_painter);
     }
 }
@@ -20,7 +23,10 @@ struct TerrainBrush2D {
 
 impl Default for TerrainBrush2D {
     fn default() -> Self {
-        TerrainBrush2D { radius: 5, tile: 4 }
+        TerrainBrush2D {
+            radius: 40,
+            tile: 8,
+        }
     }
 }
 
@@ -128,7 +134,7 @@ fn debug_painter(
                 );
                 if mouse_input.pressed(MouseButton::Left) || mouse_input.pressed(MouseButton::Right)
                 {
-                    terrain.set_texel(&pos, id, None)
+                    terrain.set_texel(&pos, Texel2D { id, ..default() }, None)
                 }
             }
         }
@@ -146,22 +152,69 @@ fn dirty_rect_visualizer(terrain: Res<Terrain2D>, mut debug_draw: ResMut<DebugLi
             continue;
         };
 
-        let color = Color::RED;
+        let offset = Vec3::from(chunk_index_to_global(chunk_index));
+        let min = offset + Vec3::from(rect.min);
+        let max = offset + Vec3::from(rect.max + Vector2I::ONE);
+        draw_box(&mut debug_draw, min, max, Color::RED, 0.0);
+    }
+}
 
-        let points = vec![
-            Vec3::new(rect.min.x as f32, rect.min.y as f32, 0.0),
-            Vec3::new((rect.max.x + 1) as f32, rect.min.y as f32, 0.0),
-            Vec3::new((rect.max.x + 1) as f32, (rect.max.y + 1) as f32, 0.0),
-            Vec3::new(rect.min.x as f32, (rect.max.y + 1) as f32, 0.0),
-        ];
-        for i in 0..points.len() {
-            let offset = Vec3::from(chunk_index_to_global(chunk_index));
-            debug_draw.line_colored(
-                offset + points[i],
-                offset + points[(i + 1) % points.len()],
-                0.0,
-                color,
+fn chunk_debugger(terrain: Res<Terrain2D>, mut debug_draw: ResMut<DebugLines>) {
+    for (chunk_index, chunk) in terrain.chunk_iter() {
+        println!("chunk contents: {chunk_index:?}");
+        let offset = Vec3::from(chunk_index_to_global(chunk_index));
+        let min = offset + Vec3::ZERO;
+        let max = offset + Vec3::from(Chunk2D::SIZE);
+        draw_box(
+            &mut debug_draw,
+            min,
+            max,
+            Color::rgba(0.5, 0.0, 0.5, 0.5),
+            0.0,
+        );
+
+        let mut tile_counter: HashMap<TexelID, (u32, u32)> = HashMap::new();
+        for y in 0..Chunk2D::SIZE_Y as i32 {
+            for x in 0..Chunk2D::SIZE_X as i32 {
+                let local = Vector2I::new(x, y);
+                let global = local_to_global(&local, chunk_index);
+                if let (Some(texel), _) = terrain.get_texel_behaviour(&global) {
+                    if !tile_counter.contains_key(&texel.id) {
+                        tile_counter.insert(texel.id, (0, 0));
+                    }
+                    let (old_count, old_density) = tile_counter[&texel.id].clone();
+                    tile_counter.insert(
+                        texel.id,
+                        (old_count + 1, old_density + texel.density as u32),
+                    );
+                }
+            }
+        }
+
+        let mut counts: Vec<(u8, String, u32, u32)> = vec![];
+
+        for (id, (count, total_density)) in tile_counter.iter() {
+            let name =
+                TexelBehaviour2D::from_id(id).map_or("unknown".to_string(), |b| b.name.to_string());
+            counts.push((*id, name, *count, *total_density));
+        }
+        counts.sort_unstable_by_key(|c| c.0);
+        for (id, name, count, total_density) in counts {
+            println!(
+                "\tmaterial: {name:<24}id: {id:<8}count: {count:<8}total_density: {total_density:<8}"
             );
         }
     }
 }
+
+pub fn draw_box(debug_draw: &mut DebugLines, min: Vec3, max: Vec3, color: Color, duration: f32) {
+    let points = vec![
+        Vec3::new(min.x, min.y, min.z),
+        Vec3::new(max.x, min.y, min.z),
+        Vec3::new(max.x, max.y, min.z),
+        Vec3::new(min.x, max.y, min.z),
+    ];
+    for i in 0..points.len() {
+        debug_draw.line_colored(points[i], points[(i + 1) % points.len()], duration, color);
+    }
+}

src/game/player.rs

@@ -81,9 +81,6 @@ pub fn player_spawn(mut commands: Commands) {
             },
             ..default()
         })
-        .insert(TransformBundle::from_transform(Transform::from_xyz(
-            256.0, 128.0, 0.0,
-        )))
         .insert(Collider::cuboid(3.0, 6.0))
         .insert(PlayerBundle {
             kinematic,
@@ -94,6 +91,6 @@ pub fn player_spawn(mut commands: Commands) {
         .insert(Sleeping::disabled())
         .insert(CameraFollow {
             priority: 1,
-            movement: FollowMovement::Smooth(18.0),
+            movement: FollowMovement::Instant,
         });
 }

src/terrain2d.rs

@@ -17,10 +17,7 @@ pub use terrain_gen2d::*;
 pub use texel2d::*;
 pub use texel_behaviour2d::*;
 
-use crate::{
-    game::camera::WORLD_WIDTH,
-    util::{frame_counter::FrameCounter, math::*, Vector2I},
-};
+use crate::util::{frame_counter::FrameCounter, math::*, Vector2I};
 
 pub struct Terrain2DPlugin;
 
@@ -46,10 +43,10 @@ impl Plugin for Terrain2DPlugin {
 
         app.register_type::<TerrainChunk2D>()
             .insert_resource(Terrain2D::new(
-                Some(WORLD_WIDTH * 2),
+                Some(Terrain2D::WORLD_HEIGHT),
                 Some(0),
                 Some(0),
-                Some(WORLD_WIDTH),
+                Some(Terrain2D::WORLD_WIDTH),
             ))
             .add_event::<TerrainEvent2D>()
             .add_system_to_stage(TerrainStages::Simulation, terrain_simulation)
@@ -74,7 +71,11 @@ pub enum TerrainStages {
     ChunkSync,
 }
 
-fn terrain_simulation(mut terrain: ResMut<Terrain2D>, frame_counter: Res<FrameCounter>) {
+fn terrain_simulation(
+    mut terrain: ResMut<Terrain2D>,
+    frame_counter: Res<FrameCounter>,
+    mut debug_draw: ResMut<bevy_prototype_debug_lines::DebugLines>,
+) {
     let simulation_frame = (frame_counter.frame % u8::MAX as u64) as u8 + 1;
 
     let indices = terrain
@@ -104,9 +105,10 @@ fn terrain_simulation(mut terrain: ResMut<Terrain2D>, frame_counter: Res<FrameCo
             } else {
                 continue;
             };
+
+            // Texel simulation
             let mut y_range: Vec<_> = (rect.min.y..rect.max.y + 1).collect();
             let mut x_range: Vec<_> = (rect.min.x..rect.max.x + 1).collect();
-
             if frame_counter.frame % 2 == 0 {
                 y_range.reverse();
             }
@@ -120,8 +122,8 @@ fn terrain_simulation(mut terrain: ResMut<Terrain2D>, frame_counter: Res<FrameCo
                     let global = local_to_global(&local, &chunk_index);
 
                     if terrain
-                        .get_texel(&global)
-                        .map_or(true, |t| t.last_simulation == simulation_frame)
+                        .get_latest_simulation(&global)
+                        .map_or(true, |frame| frame == simulation_frame)
                     {
                         continue;
                     };
@@ -129,6 +131,172 @@ fn terrain_simulation(mut terrain: ResMut<Terrain2D>, frame_counter: Res<FrameCo
                     simulate_texel(global, &mut terrain, &frame_counter);
                 }
             }
+
+            // Gas dispersion
+            let alternate_dispersion = frame_counter.frame % 2 == 0;
+            let alternate = if alternate_dispersion { 1 } else { 0 };
+            let y_range =
+                ((rect.min.y - alternate)..rect.max.y + 1 + alternate).collect::<Vec<_>>();
+            let x_range =
+                ((rect.min.x - alternate)..rect.max.x + 1 + alternate).collect::<Vec<_>>();
+            const DISPERSION_WIDTH: usize = 2;
+            const DISPERSION_HEIGHT: usize = 2;
+            for y_arr in y_range.chunks(DISPERSION_HEIGHT) {
+                for x_arr in x_range.chunks(DISPERSION_WIDTH) {
+                    let mut global_positions = vec![];
+                    for y in y_arr.iter() {
+                        for x in x_arr.iter() {
+                            let local = Vector2I::new(*x, *y);
+                            let global = local_to_global(&local, &chunk_index);
+                            global_positions.push(global);
+                        }
+                    }
+
+                    // Distribute gas
+                    disperse_gas(
+                        global_positions,
+                        &mut terrain,
+                        &frame_counter,
+                        &mut debug_draw,
+                    )
+                }
+            }
+        }
+    }
+}
+
+// TODO: Don't update if the result of dispersion is similar to before
+fn disperse_gas(
+    global_positions: Vec<Vector2I>,
+    terrain: &mut Terrain2D,
+    frame_counter: &FrameCounter,
+    debug_draw: &mut bevy_prototype_debug_lines::DebugLines,
+) {
+    use u32 as Capacity;
+    use u8 as Min;
+    use u8 as Max;
+    let mut total_densities: HashMap<TexelID, (Capacity, Min, Max)> = HashMap::new();
+    let mut valid_globals = vec![];
+    for global in global_positions.iter() {
+        let (texel, behaviour) = terrain.get_texel_behaviour(global);
+        if behaviour.clone().map_or(true, |b| b.form == TexelForm::Gas) {
+            valid_globals.push(*global);
+        }
+        match (texel, behaviour) {
+            (Some(texel), Some(behaviour)) => {
+                if behaviour.form == TexelForm::Gas {
+                    if let Some((old_density, old_min, old_max)) = total_densities.get(&texel.id) {
+                        total_densities.insert(
+                            texel.id,
+                            (
+                                texel.density as u32 + *old_density,
+                                texel.density.min(*old_min),
+                                texel.density.max(*old_max),
+                            ),
+                        );
+                    } else {
+                        total_densities.insert(
+                            texel.id,
+                            (texel.density as u32, texel.density, texel.density),
+                        );
+                    }
+                }
+            }
+            (_, _) => (),
+        }
+    }
+
+    let mut total_densities: Vec<(TexelID, Capacity, Min, Max)> = total_densities
+        .iter()
+        .map(|(t, (d, min, max))| (*t, *d, *min, *max))
+        .collect();
+
+    if total_densities.len() == 0 {
+        return;
+    }
+
+    total_densities.sort_unstable_by_key(|(_, density, _, _)| *density);
+    total_densities.reverse();
+
+    const TILE_CAPACITY: u32 = u8::MAX as u32;
+    let free_slots = valid_globals.len() as u32
+        - total_densities
+            .iter()
+            .map(|(_, v, _, _)| (*v / (TILE_CAPACITY + 1)) + 1)
+            .sum::<u32>();
+
+    // Stop if the gas is already close to a stable state
+    const STABLE_TRESHOLD: u8 = 3;
+    if total_densities.iter().all(|(_, _, min, max)| {
+        if u8::abs_diff(*min, *max) > STABLE_TRESHOLD {
+            return false;
+        }
+        free_slots > 0 && *max <= STABLE_TRESHOLD
+    }) {
+        // // DEBUG: draw box for stabilized area
+        // let mut min = valid_globals.first().unwrap().clone();
+        // let mut max = valid_globals.first().unwrap().clone();
+        // for global in valid_globals.iter() {
+        //     min = Vector2I::min(&min, global);
+        //     max = Vector2I::max(&max, global);
+        // }
+        // max = max + Vector2I::ONE;
+        // crate::game::debug::terrain::draw_box(
+        //     debug_draw,
+        //     Vec3::from(min),
+        //     Vec3::from(max),
+        //     Color::CYAN,
+        //     0.0,
+        // );
+        return;
+    }
+
+    // Allocate slots
+    let mut slots: Vec<(TexelID, u32)> = vec![];
+    for (id, density, _, _) in total_densities.iter() {
+        let min_slots = (density / (TILE_CAPACITY + 1)) + 1;
+        slots.push((*id, min_slots));
+    }
+    for i in 0..free_slots as usize {
+        let len = slots.len();
+        slots[i % len].1 += 1;
+    }
+
+    // Disperse into given slots
+    let mut texels: Vec<Texel2D> = vec![];
+    for (id, total_density, _, _) in total_densities.iter() {
+        let slots = slots.iter().find(|s| s.0 == *id).unwrap().1;
+        let mut density_left = *total_density;
+        for i in 0..slots {
+            let density = if i < (slots - 1) {
+                (total_density / slots).min(density_left)
+            } else {
+                density_left
+            }
+            .min(u8::MAX as u32);
+            if density > 0 {
+                texels.push(Texel2D {
+                    id: *id,
+                    density: density as u8,
+                });
+                density_left -= density;
+            }
+        }
+    }
+
+    // Apply changes
+    if texels.len() > valid_globals.len() {
+        panic!("disperse_gas() - valid_globals is shorter than texels");
+    }
+
+    fastrand::shuffle(&mut valid_globals);
+    for i in 0..valid_globals.len() {
+        let global = valid_globals[i];
+        if i < texels.len() {
+            let texel = texels[i];
+            terrain.set_texel(&global, texel, None);
+        } else {
+            terrain.set_texel(&global, Texel2D::default(), None)
         }
     }
 }
@@ -146,29 +314,37 @@ fn simulate_texel(global: Vector2I, terrain: &mut Terrain2D, frame_counter: &Fra
         let grav_offset = Vector2I::from(gravity);
         let grav_pos = global + grav_offset;
 
-        // Try falling
-        {
-            let (_, other_behaviour) = terrain.get_texel_behaviour(&grav_pos);
-            if TexelBehaviour2D::can_displace(&behaviour, &other_behaviour) {
-                terrain.swap_texels(&global, &grav_pos, Some(simulation_frame));
-                return;
+        if behaviour.form != TexelForm::Gas || gravity.abs() > fastrand::u8(0..u8::MAX) {
+            // Try falling
+            {
+                let (_, other_behaviour) = terrain.get_texel_behaviour(&grav_pos);
+                if TexelBehaviour2D::can_displace(&behaviour, &other_behaviour) {
+                    terrain.swap_texels(&global, &grav_pos, Some(simulation_frame));
+                    return;
+                }
+                if terrain.can_transfer_density(&global, &grav_pos) {
+                    terrain.transfer_density(&global, &grav_pos, gravity, Some(simulation_frame))
+                }
             }
-        }
 
-        // Try "sliding"
-        let mut dirs = vec![Vector2I::RIGHT, Vector2I::LEFT];
-        if ((frame_counter.frame / 73) % 2) as i32 == global.y % 2 {
-            dirs.reverse();
-        }
-        for dir in dirs.iter() {
-            let slide_pos = match behaviour.form {
-                TexelForm::Solid => grav_pos + *dir,
-                TexelForm::Liquid | TexelForm::Gas => global + *dir,
-            };
-            let (_, other_behaviour) = terrain.get_texel_behaviour(&slide_pos);
-            if TexelBehaviour2D::can_displace(&behaviour, &other_behaviour) {
-                terrain.swap_texels(&global, &slide_pos, Some(simulation_frame));
-                return;
+            // Try "sliding"
+            let mut dirs = vec![Vector2I::RIGHT, Vector2I::LEFT];
+            if ((frame_counter.frame / 73) % 2) as i32 == global.y % 2 {
+                dirs.reverse();
+            }
+            for dir in dirs.iter() {
+                let slide_pos = match behaviour.form {
+                    TexelForm::Solid => grav_pos + *dir,
+                    TexelForm::Liquid | TexelForm::Gas => global + *dir,
+                };
+                let (_, other_behaviour) = terrain.get_texel_behaviour(&slide_pos);
+                if TexelBehaviour2D::can_displace(&behaviour, &other_behaviour) {
+                    terrain.swap_texels(&global, &slide_pos, Some(simulation_frame));
+                    return;
+                }
+                if terrain.can_transfer_density(&global, &grav_pos) {
+                    terrain.transfer_density(&global, &grav_pos, gravity, Some(simulation_frame))
+                }
             }
         }
     }
@@ -205,13 +381,16 @@ pub struct Terrain2D {
 }
 
 impl Terrain2D {
+    pub const WORLD_WIDTH: i32 = 512;
+    pub const WORLD_HEIGHT: i32 = Self::WORLD_WIDTH * 2;
+
     pub fn new(
         top_boundary: Option<i32>,
         bottom_boundary: Option<i32>,
         left_boundary: Option<i32>,
         right_boundary: Option<i32>,
-    ) -> Terrain2D {
-        Terrain2D {
+    ) -> Self {
+        Self {
             chunk_map: HashMap::new(),
             events: Vec::new(),
             top_boundary,
@@ -278,7 +457,7 @@ impl Terrain2D {
 
     pub fn is_within_boundaries(&self, global: &Vector2I) -> bool {
         if let Some(top) = self.top_boundary {
-            if global.y > top {
+            if global.y >= top {
                 return false;
             }
         }
@@ -293,7 +472,7 @@ impl Terrain2D {
             }
         }
         if let Some(right) = self.right_boundary {
-            if global.x > right {
+            if global.x >= right {
                 return false;
             }
         }
@@ -305,6 +484,12 @@ impl Terrain2D {
             .map_or(None, |chunk| chunk.get_texel(&global_to_local(global)))
     }
 
+    pub fn get_latest_simulation(&self, global: &Vector2I) -> Option<u8> {
+        self.global_to_chunk(global).map_or(None, |chunk| {
+            chunk.get_latest_simulation(&global_to_local(global))
+        })
+    }
+
     pub fn get_texel_behaviour(
         &self,
         global: &Vector2I,
@@ -320,16 +505,22 @@ impl Terrain2D {
         )
     }
 
-    pub fn set_texel(&mut self, global: &Vector2I, id: TexelID, simulation_frame: Option<u8>) {
+    pub fn set_texel(
+        &mut self,
+        global: &Vector2I,
+        new_texel: Texel2D,
+        simulation_frame: Option<u8>,
+    ) {
         if !self.is_within_boundaries(global) {
             return;
         }
         let index = global_to_chunk_index(global);
         let changed = match self.index_to_chunk_mut(&index) {
-            Some(chunk) => chunk.set_texel(&global_to_local(global), id, simulation_frame),
+            Some(chunk) => chunk.set_texel(&global_to_local(global), new_texel, simulation_frame),
             None => {
                 let mut chunk = Chunk2D::new();
-                let changed = chunk.set_texel(&global_to_local(global), id, simulation_frame);
+                let changed =
+                    chunk.set_texel(&global_to_local(global), new_texel, simulation_frame);
                 self.add_chunk(index, chunk);
                 changed
             }
@@ -348,11 +539,71 @@ impl Terrain2D {
         to_global: &Vector2I,
         simulation_frame: Option<u8>,
     ) {
-        let from = self.get_texel(from_global).map_or(0, |t| t.id);
-        let to = self.get_texel(to_global).map_or(0, |t| t.id);
+        let from = self.get_texel(from_global).unwrap_or_default();
+        let to = self.get_texel(to_global).unwrap_or_default();
         self.set_texel(to_global, from, simulation_frame);
+        // REM: The displaced texel is also marked as simulated
         self.set_texel(from_global, to, simulation_frame);
     }
+
+    fn can_transfer_density(&self, from_global: &Vector2I, to_global: &Vector2I) -> bool {
+        let from = self.get_texel(from_global).unwrap_or_default();
+        let to = self.get_texel(to_global).unwrap_or_default();
+        if from.id != to.id {
+            return false;
+        }
+
+        let behaviour = if let Some(behaviour) = from.behaviour() {
+            behaviour
+        } else {
+            return false;
+        };
+
+        behaviour.form == TexelForm::Gas
+    }
+
+    fn transfer_density(
+        &mut self,
+        from_global: &Vector2I,
+        to_global: &Vector2I,
+        gravity: TexelGravity,
+        simulation_frame: Option<u8>,
+    ) {
+        let from = self.get_texel(from_global).unwrap_or_default();
+        let to = self.get_texel(to_global).unwrap_or_default();
+        let max_transfer = gravity.abs();
+
+        // DEBUG: Test this out, another property?
+        const MAX_TARGET_DENSITY: u8 = 25;
+        let transfer = (u8::MAX - to.density)
+            .min(max_transfer)
+            .min(from.density)
+            .min(MAX_TARGET_DENSITY.max(to.density) - to.density);
+        if transfer == 0 {
+            return;
+        }
+
+        if from.density - transfer == 0 {
+            self.set_texel(&from_global, Texel2D::default(), simulation_frame);
+        } else {
+            self.set_texel(
+                &from_global,
+                Texel2D {
+                    density: from.density - transfer,
+                    ..from
+                },
+                simulation_frame,
+            );
+        }
+        self.set_texel(
+            &to_global,
+            Texel2D {
+                density: to.density + transfer,
+                ..to
+            },
+            simulation_frame,
+        );
+    }
 }
 
 pub fn local_to_texel_index(position: &Vector2I) -> Option<usize> {

src/terrain2d/chunk2d.rs

@@ -1,18 +1,13 @@
 use std::collections::VecDeque;
 
-use super::{
-    local_to_texel_index, texel_index_to_local, Terrain2D, TerrainEvent2D, Texel2D,
-    TexelBehaviour2D, TexelID, NEIGHBOUR_INDEX_MAP,
-};
+use super::*;
 use crate::util::{CollisionLayers, Segment2I, Vector2I};
-use bevy::{
-    prelude::*,
-    render::{render_resource::Extent3d, texture::ImageSampler},
-};
-use bevy_rapier2d::prelude::*;
+use bevy::render::{render_resource::Extent3d, texture::ImageSampler};
 use lazy_static::lazy_static;
 
 type Island = VecDeque<Segment2I>;
+pub type Chunk2DIndex = Vector2I;
+pub type NeighbourMask = u8;
 
 lazy_static! {
     /// Marching Square case dictionary.
@@ -49,6 +44,14 @@ lazy_static! {
         /* down  */ Segment2I { from: Vector2I::RIGHT, to: Vector2I::ZERO },
         /* left  */ Segment2I { from: Vector2I::ZERO, to: Vector2I::UP },
     ];
+
+    static ref NEIGHBOUR_INDEX_MAP: HashMap<Vector2I, u8> = {
+        let mut map = HashMap::new();
+        for i in 0..Chunk2D::NEIGHBOUR_OFFSET_VECTORS.len() {
+            map.insert(Chunk2D::NEIGHBOUR_OFFSET_VECTORS[i], i as u8);
+        }
+        map
+    };
 }
 
 #[derive(Reflect, Component, Default)]
@@ -79,8 +82,6 @@ pub struct ChunkColliderBundle {
     pub transform: TransformBundle,
 }
 
-pub type Chunk2DIndex = Vector2I;
-
 #[derive(Clone, Copy)]
 pub struct ChunkRect {
     pub min: Vector2I,
@@ -97,7 +98,11 @@ impl ChunkRect {
 }
 
 pub struct Chunk2D {
-    pub texels: [Texel2D; (Self::SIZE_X * Self::SIZE_Y) as usize],
+    pub texels: [Texel2D; Self::SIZE_X * Self::SIZE_Y],
+    /// bitmask of empty/non-empty neighbours, see NEIGHBOUR_OFFSET_VECTORS for the order
+    pub neighbour_mask: [NeighbourMask; Self::SIZE_X * Self::SIZE_Y],
+    /// Used in simulation step so that texels won't be updated twice. Value of 0 is always updated.
+    pub simulation_frames: [u8; Self::SIZE_X * Self::SIZE_Y],
     // TODO: handle multiple dirty rects?
     pub dirty_rect: Option<ChunkRect>,
 }
@@ -109,65 +114,22 @@ impl Chunk2D {
         x: Self::SIZE_X as i32,
         y: Self::SIZE_Y as i32,
     };
+    pub const NEIGHBOUR_OFFSET_VECTORS: [Vector2I; 4] = [
+        Vector2I { x: 0, y: 1 },
+        Vector2I { x: 1, y: 0 },
+        Vector2I { x: 0, y: -1 },
+        Vector2I { x: -1, y: 0 },
+    ];
 
     pub fn new() -> Chunk2D {
         Chunk2D {
-            texels: Self::new_texel_array(),
+            texels: [Texel2D::default(); Self::SIZE_X * Self::SIZE_Y],
+            neighbour_mask: [0; Self::SIZE_X * Self::SIZE_Y],
+            simulation_frames: [0; Self::SIZE_X * Self::SIZE_Y],
             dirty_rect: None,
         }
     }
 
-    pub fn new_full() -> Chunk2D {
-        let mut chunk = Chunk2D {
-            texels: Self::new_texel_array(),
-            dirty_rect: None,
-        };
-        for y in 0..Self::SIZE_Y {
-            for x in 0..Self::SIZE_X {
-                chunk.set_texel(&Vector2I::new(x as i32, y as i32), 1, None);
-            }
-        }
-        chunk
-    }
-
-    pub fn new_half() -> Chunk2D {
-        let mut chunk = Chunk2D {
-            texels: Self::new_texel_array(),
-            dirty_rect: None,
-        };
-        for y in 0..Self::SIZE_Y {
-            for x in 0..Self::SIZE_X {
-                if x <= Self::SIZE_Y - y {
-                    chunk.set_texel(&Vector2I::new(x as i32, y as i32), 1, None);
-                }
-            }
-        }
-        chunk
-    }
-
-    pub fn new_circle() -> Chunk2D {
-        let mut chunk = Chunk2D {
-            texels: Self::new_texel_array(),
-            dirty_rect: None,
-        };
-        let origin = Self::SIZE / 2;
-        let radius = Self::SIZE_X as i32 / 2;
-        for y in 0..Self::SIZE_Y {
-            for x in 0..Self::SIZE_X {
-                let dx = (x as i32 - origin.x).abs();
-                let dy = (y as i32 - origin.y).abs();
-                if dx * dx + dy * dy <= (radius - 1) * (radius - 1) {
-                    chunk.set_texel(&Vector2I::new(x as i32, y as i32), 1, None);
-                }
-            }
-        }
-        chunk
-    }
-
-    pub fn new_texel_array() -> [Texel2D; Self::SIZE_X * Self::SIZE_Y] {
-        [Texel2D::default(); Self::SIZE_X * Self::SIZE_Y]
-    }
-
     pub fn xy_vec() -> Vec<Vector2I> {
         let mut result = Vec::with_capacity(Self::SIZE_X * Self::SIZE_Y);
         for y in 0..Self::SIZE_Y {
@@ -208,6 +170,10 @@ impl Chunk2D {
         local_to_texel_index(position).map(|i| self.texels[i])
     }
 
+    pub fn get_latest_simulation(&self, position: &Vector2I) -> Option<u8> {
+        local_to_texel_index(position).map(|i| self.simulation_frames[i])
+    }
+
     pub fn get_texel_mut(&mut self, position: &Vector2I) -> Option<&mut Texel2D> {
         local_to_texel_index(position).map(|i| &mut self.texels[i])
     }
@@ -215,46 +181,44 @@ impl Chunk2D {
     pub fn set_texel(
         &mut self,
         position: &Vector2I,
-        id: TexelID,
+        new_texel: Texel2D,
         simulation_frame: Option<u8>,
     ) -> bool {
         let i = local_to_texel_index(position).expect("Texel index out of range");
-        if self.texels[i].id != id {
-            self.mark_dirty(position);
+        if self.texels[i] == new_texel {
+            return false;
         }
-        let update_neighbours = TexelBehaviour2D::has_collision(&self.texels[i].id)
-            != TexelBehaviour2D::has_collision(&id);
-        let changed = self.texels[i].id != id;
-        self.texels[i].id = id;
+        self.mark_dirty(position);
+        let update_neighbours = self.texels[i].has_collision() != new_texel.has_collision();
+        self.texels[i] = new_texel;
+        // Update simulation frame
         if let Some(simulation_frame) = simulation_frame {
-            self.texels[i].last_simulation = simulation_frame;
+            self.simulation_frames[i] = simulation_frame;
         }
         // Update neighbour mask
         if update_neighbours {
-            for offset in Texel2D::NEIGHBOUR_OFFSET_VECTORS {
+            for offset in Self::NEIGHBOUR_OFFSET_VECTORS {
                 // Flip neighbour's bit
-                match self.get_texel_mut(&(*position + offset)) {
-                    Some(mut neighbour) => {
-                        neighbour.neighbour_mask ^= 1 << NEIGHBOUR_INDEX_MAP[&-offset];
+                match local_to_texel_index(&(*position + offset)) {
+                    Some(index) => {
+                        self.neighbour_mask[index] ^= 1 << NEIGHBOUR_INDEX_MAP[&-offset];
                     }
                     None => (),
                 }
             }
         }
-        changed
+        true
     }
 
     pub fn create_texture_data(&self) -> Vec<u8> {
         let mut image_data = Vec::with_capacity(Chunk2D::SIZE_X * Chunk2D::SIZE_Y * 4);
         for y in (0..Chunk2D::SIZE_Y).rev() {
             for x in 0..Chunk2D::SIZE_X {
-                let id = &self
-                    .get_texel(&Vector2I::new(x as i32, y as i32))
-                    .unwrap()
-                    .id;
-                let behaviour = TexelBehaviour2D::from_id(id);
-                let color =
+                let texel = &self.get_texel(&Vector2I::new(x as i32, y as i32)).unwrap();
+                let behaviour = texel.behaviour();
+                let mut color =
                     behaviour.map_or(Color::rgba_u8(0, 0, 0, 0), |behaviour| behaviour.color);
+                color.set_a(color.a() * ((texel.density as f32) / 256.0));
                 let color_data = color.as_rgba_u32();
                 let mut color_data: Vec<u8> = vec![
                     ((color_data >> 0) & 0xff) as u8,
@@ -268,6 +232,7 @@ impl Chunk2D {
         image_data
     }
 
+    // TODO: Don't create collision for falling texels, it's pretty annoying that a stream of small grains blocks movement
     pub fn create_collision_data(&self) -> Vec<Vec<Vec2>> {
         let mut islands: Vec<Island> = Vec::new();
         for i in 0..self.texels.len() {
@@ -287,7 +252,7 @@ impl Chunk2D {
             let mut sides: Vec<Segment2I>;
             let has_collision = TexelBehaviour2D::has_collision(&self.texels[i].id);
             if !has_collision {
-                sides = MST_CASE_MAP[self.texels[i].neighbour_mask as usize]
+                sides = MST_CASE_MAP[self.neighbour_mask[i] as usize]
                     .iter()
                     .clone()
                     .map(|side| Segment2I {
@@ -473,9 +438,7 @@ pub fn chunk_spawner(
     }
 }
 
-/**
-    Update the chunk sprite as needed
-*/
+/// Update the chunk sprite as needed
 pub fn chunk_sprite_sync(
     mut terrain_events: EventReader<TerrainEvent2D>,
     mut images: ResMut<Assets<Image>>,
@@ -532,9 +495,7 @@ pub fn chunk_sprite_sync(
     }
 }
 
-/**
-    Create and update colliders for chunk as needed
-*/
+/// Create and update colliders for chunk as needed
 pub fn chunk_collision_sync(
     mut terrain_events: EventReader<TerrainEvent2D>,
     mut commands: Commands,

src/terrain2d/terrain_gen2d.rs

@@ -1,6 +1,7 @@
 use noise::{NoiseFn, PerlinSurflet};
 
-use super::{chunk_index_to_global, Chunk2D, Chunk2DIndex};
+use super::*;
+use crate::util::{inverse_lerp, lerp};
 
 pub struct TerrainGen2D {
     pub seed: u32,
@@ -39,7 +40,7 @@ impl TerrainGen2D {
                 id = 13;
             }
 
-            chunk.set_texel(&local, id, None);
+            chunk.set_texel(&local, Texel2D { id, ..default() }, None);
         }
         chunk
     }

src/terrain2d/texel2d.rs

@@ -1,35 +1,32 @@
-use lazy_static::lazy_static;
-use std::collections::HashMap;
-
 pub use u8 as TexelID;
-pub use u8 as NeighbourMask;
 
-use crate::util::Vector2I;
+use super::TexelBehaviour2D;
 
-#[derive(Clone, Copy, Default)]
+#[derive(Clone, Copy, Debug, PartialEq)]
 pub struct Texel2D {
+    /// Identifier for a set of properties
     pub id: TexelID,
-    /// bitmask of empty/non-empty neighbours, see NEIGHBOUR_OFFSET_VECTORS for the order
-    pub neighbour_mask: NeighbourMask,
-    pub last_simulation: u8,
+    /// Used by gas materials
+    pub density: u8,
 }
 
-lazy_static! {
-    pub static ref NEIGHBOUR_INDEX_MAP: HashMap<Vector2I, u8> = {
-        let mut map = HashMap::new();
-        for i in 0..Texel2D::NEIGHBOUR_OFFSET_VECTORS.len() {
-            map.insert(Texel2D::NEIGHBOUR_OFFSET_VECTORS[i], i as u8);
+impl Default for Texel2D {
+    fn default() -> Self {
+        Self {
+            id: TexelID::default(),
+            density: u8::MAX,
         }
-        map
-    };
+    }
 }
 
 impl Texel2D {
     pub const EMPTY: TexelID = 0;
-    pub const NEIGHBOUR_OFFSET_VECTORS: [Vector2I; 4] = [
-        Vector2I { x: 0, y: 1 },
-        Vector2I { x: 1, y: 0 },
-        Vector2I { x: 0, y: -1 },
-        Vector2I { x: -1, y: 0 },
-    ];
+
+    pub fn has_collision(&self) -> bool {
+        TexelBehaviour2D::has_collision(&self.id)
+    }
+
+    pub fn behaviour(&self) -> Option<TexelBehaviour2D> {
+        TexelBehaviour2D::from_id(&self.id)
+    }
 }

src/terrain2d/texel_behaviour2d.rs

@@ -14,7 +14,7 @@ lazy_static! {
             TexelBehaviour2D {
                 name: Cow::Borrowed("loose sand"),
                 color: Color::rgb(0.61, 0.49, 0.38),
-                gravity: Some(TexelGravity::Down(100)),
+                gravity: Some(TexelGravity::Down(200)),
                 has_collision: true,
                 ..default()
             },
@@ -25,7 +25,7 @@ lazy_static! {
             TexelBehaviour2D {
                 name: Cow::Borrowed("loose stone"),
                 color: Color::rgb(0.21, 0.19, 0.17),
-                gravity: Some(TexelGravity::Down(100)),
+                gravity: Some(TexelGravity::Down(200)),
                 has_collision: true,
                 ..default()
             },
@@ -36,7 +36,7 @@ lazy_static! {
             TexelBehaviour2D {
                 name: Cow::Borrowed("loose sturdy stone"),
                 color: Color::rgb(0.11, 0.11, 0.11),
-                gravity: Some(TexelGravity::Down(100)),
+                gravity: Some(TexelGravity::Down(200)),
                 has_collision: true,
                 ..default()
             },
@@ -48,7 +48,7 @@ lazy_static! {
                 name: Cow::Borrowed("water"),
                 color: Color::rgba(0.0, 0.0, 1.0, 0.5),
                 form: TexelForm::Liquid,
-                gravity: Some(TexelGravity::Down(10)),
+                gravity: Some(TexelGravity::Down(50)),
                 ..default()
             },
         );
@@ -57,9 +57,9 @@ lazy_static! {
             5,
             TexelBehaviour2D {
                 name: Cow::Borrowed("oil"),
-                color: Color::rgba(0.0, 1.0, 0.0, 0.5),
-                form: TexelForm::Gas,
-                gravity: Some(TexelGravity::Up(50)),
+                color: Color::rgba(0.5, 0.5, 0.25, 0.5),
+                form: TexelForm::Liquid,
+                gravity: Some(TexelGravity::Down(20)),
                 ..default()
             },
         );
@@ -67,10 +67,31 @@ lazy_static! {
         result.insert(
             6,
             TexelBehaviour2D {
-                name: Cow::Borrowed("gas"),
-                color: Color::rgba(0.5, 0.5, 0.25, 0.5),
-                form: TexelForm::Liquid,
-                gravity: Some(TexelGravity::Down(5)),
+                name: Cow::Borrowed("light gas"),
+                color: Color::rgba(0.0, 1.0, 0.0, 0.5),
+                form: TexelForm::Gas,
+                gravity: Some(TexelGravity::Up(160)),
+                ..default()
+            },
+        );
+
+        result.insert(
+            7,
+            TexelBehaviour2D {
+                name: Cow::Borrowed("heavy gas"),
+                color: Color::rgba(1.0, 0.5, 0.5, 0.5),
+                form: TexelForm::Gas,
+                gravity: Some(TexelGravity::Down(60)),
+                ..default()
+            },
+        );
+
+        result.insert(
+            8,
+            TexelBehaviour2D {
+                name: Cow::Borrowed("oxygen"),
+                color: Color::rgba(0.5, 0.5, 0.5, 0.5),
+                form: TexelForm::Gas,
                 ..default()
             },
         );
@@ -107,9 +128,16 @@ lazy_static! {
 
         result
     };
+    static ref FORM_DISPLACEMENT_PRIORITY: HashMap<TexelForm, u8> = {
+        let mut result = HashMap::new();
+        result.insert(TexelForm::Gas, 0);
+        result.insert(TexelForm::Liquid, 1);
+        result.insert(TexelForm::Solid, 2);
+        result
+    };
 }
 
-#[derive(Clone, Copy, Default, PartialEq)]
+#[derive(Clone, Copy, Debug, Default, PartialEq, Eq, Hash)]
 pub enum TexelForm {
     #[default]
     // Solid materials, when affected by gravity, create pyramid-like piles
@@ -120,7 +148,16 @@ pub enum TexelForm {
     Gas,
 }
 
-#[derive(Clone, Copy, PartialEq)]
+impl TexelForm {
+    fn priority(&self) -> u8 {
+        FORM_DISPLACEMENT_PRIORITY
+            .get(self)
+            .cloned()
+            .unwrap_or_default()
+    }
+}
+
+#[derive(Clone, Copy, Debug, PartialEq)]
 pub enum TexelGravity {
     Down(u8),
     Up(u8),
@@ -135,7 +172,16 @@ impl From<TexelGravity> for Vector2I {
     }
 }
 
-#[derive(Clone)]
+impl TexelGravity {
+    pub fn abs(&self) -> u8 {
+        match self {
+            TexelGravity::Down(grav) => *grav,
+            TexelGravity::Up(grav) => *grav,
+        }
+    }
+}
+
+#[derive(Clone, Debug)]
 pub struct TexelBehaviour2D {
     pub name: Cow<'static, str>,
     pub color: Color,
@@ -185,7 +231,10 @@ impl TexelBehaviour2D {
         let to = if let Some(to) = to { to } else { return true };
 
         match (from.form, to.form) {
-            (_, to_form) => {
+            (from_form, to_form) => {
+                if from_form.priority() != to_form.priority() {
+                    return from_form.priority() > to_form.priority();
+                }
                 if let (Some(from_grav), Some(to_grav)) = (from.gravity, to.gravity) {
                     match (from_grav, to_grav) {
                         (TexelGravity::Down(from_grav), TexelGravity::Down(to_grav)) => {