Apparently the bounce is still broken. It always was.

src/cell.rs

@@ -1,5 +1,4 @@
 use core::fmt;
-use std::fmt::write;
 
 #[derive(Clone, Copy, Debug, PartialEq)]
 pub enum CellVariance {
@@ -33,4 +32,12 @@ impl Cell {
     pub fn new(variance: CellVariance) -> Self {
         Self { variance }
     }
+
+    pub fn invert(&self) -> Self {
+        Cell::new(match self.variance {
+            CellVariance::DAY => CellVariance::NIGHT,
+            CellVariance::NIGHT => CellVariance::DAY,
+            CellVariance::VOID => CellVariance::VOID
+        })
+    }
 }

src/direction.rs

@@ -1,11 +1,16 @@
 #[derive(Clone, Debug)]
-pub struct Direction {
+pub struct Coord {
     pub x: isize,
     pub y: isize
 }
 
-impl Direction {
+impl Coord {
     pub fn new(x: isize, y: isize) -> Self {
         Self { x, y }
     }
+
+    pub fn invert(&mut self) {
+        self.x *= -1;
+        self.y *= -1;
+    }
 }

src/main.rs

@@ -9,12 +9,12 @@ use winit::{
     dpi::LogicalSize,
     event::{Event, VirtualKeyCode},
     event_loop::{ControlFlow, EventLoop},
-    window::{self, WindowBuilder},
+    window::WindowBuilder,
 };
 use winit_input_helper::WinitInputHelper;
 
-const WIDTH: u32 = 64;
-const HEIGHT: u32 = 64;
+const WIDTH: usize = 64;
+const HEIGHT: usize = 64;
 const SCALE_FACTOR: f64 = 10.0;
 
 fn main() -> Result<(), Error> {
@@ -39,7 +39,7 @@ fn main() -> Result<(), Error> {
     let mut pixels = {
         let window_size = window.inner_size();
         let surface_texture = SurfaceTexture::new(window_size.width, window_size.height, &window);
-        Pixels::new(WIDTH, HEIGHT, surface_texture)?
+        Pixels::new(WIDTH as u32, HEIGHT as u32, surface_texture)?
     };
 
     let mut stage = Stage::new(WIDTH as usize, HEIGHT as usize);
@@ -47,13 +47,11 @@ fn main() -> Result<(), Error> {
 
     let mut paused = false;
 
-    let mut draw_state: Option<bool> = None;
-
     event_loop.run(move |event, _, control_flow| {
         if let Event::RedrawRequested(_) = event {
             stage.draw(pixels.frame_mut());
 
-            if let Err(err) = pixels.render() {
+            if let Err(_) = pixels.render() {
                 debug_assert!(true, "Oops, I did it again.");
 
                 *control_flow = ControlFlow::Exit;
@@ -80,9 +78,13 @@ fn main() -> Result<(), Error> {
                 stage.scatter(stage::ScatterTypes::Random);
             }
 
+            if input.key_pressed(VirtualKeyCode::H) {
+                stage.scatter(stage::ScatterTypes::HalfVertical);
+            }
+
             // Handle mouse. This is a bit involved since support some simple
             // line drawing (mostly because it makes nice looking patterns).
-            let (mouse_cell, mouse_prev_cell) = input
+            let (mouse_cell, _) = input
                 .mouse()
                 .map(|(mx, my)| {
                     let (dx, dy) = input.mouse_diff();
@@ -116,7 +118,7 @@ fn main() -> Result<(), Error> {
     
             // Resize the window
             if let Some(size) = input.window_resized() {
-                if let Err(err) = pixels.resize_surface(size.width, size.height) {
+                if let Err(_) = pixels.resize_surface(size.width, size.height) {
                     debug_assert!(true, "Resize failed!");
                     *control_flow = ControlFlow::Exit;
                     return;

src/npc.rs

@@ -1,4 +1,27 @@
-use crate::{cell::CellVariance, direction::Direction};
+use std::cell;
+
+use crate::{
+    cell::{Cell, CellVariance},
+    direction::Coord,
+    stage::{self, Stage},
+    HEIGHT, WIDTH,
+};
+
+#[derive(Clone, Debug, PartialEq)]
+pub enum Direction {
+    TOP,    /* 💪 */
+    BOTTOM, /* 👉👈🥺 */
+    LEFT,
+    RIGHT,
+}
+
+#[derive(Clone, Debug)]
+pub struct Neighbour {
+    pub cell: Cell,
+    pub direction: Direction,
+    pub pos_x: usize,
+    pub pos_y: usize,
+}
 
 #[derive(Clone, Debug)]
 pub struct NPC {
@@ -6,19 +29,159 @@ pub struct NPC {
     pub obstructed_from: Vec<CellVariance>,
     pub pos_x: usize,
     pub pos_y: usize,
-    pub direction: Direction
+    pub direction: Coord,
 }
 
 impl NPC {
-    pub fn new(pos_x: usize, pos_y: usize, direction: Direction, walk_on: CellVariance, obstructed_from: Vec<CellVariance>) -> Self {
-        Self { walk_on, obstructed_from, pos_x, pos_y, direction }
+    pub fn new_day(pos_x: usize, pos_y: usize, direction: Coord) -> Self {
+        Self {
+            walk_on: CellVariance::DAY,
+            obstructed_from: vec![CellVariance::NIGHT, CellVariance::VOID],
+            pos_x,
+            pos_y,
+            direction,
+        }
     }
 
-    pub fn new_day(pos_x: usize, pos_y: usize, direction: Direction) -> Self {
-        Self { walk_on: CellVariance::DAY, obstructed_from: vec![CellVariance::NIGHT], pos_x, pos_y, direction }
+    pub fn new_night(pos_x: usize, pos_y: usize, direction: Coord) -> Self {
+        Self {
+            walk_on: CellVariance::NIGHT,
+            obstructed_from: vec![CellVariance::DAY, CellVariance::VOID],
+            pos_x,
+            pos_y,
+            direction,
+        }
     }
 
-    pub fn new_night(pos_x: usize, pos_y: usize, direction: Direction) -> Self {
-        Self { walk_on: CellVariance::NIGHT, obstructed_from: vec![CellVariance::DAY], pos_x, pos_y, direction }
+    pub fn into_cell(&self) -> Cell {
+        // TODO: Bad idea.
+        Cell::new(self.obstructed_from[0])
+    }
+
+    pub fn process_bounce(&mut self, map: &Vec<Cell>) -> Option<Neighbour> {
+        // Get the current and next positions
+        
+        let mut next_direction = self.direction.clone();
+        
+        // If we are here, we know that we hit something.
+        match self.check_neighborhood(map) {
+            None => {
+                self.move_next();
+                return None;
+            }
+            Some(neighbour) => {
+                if neighbour.direction == Direction::LEFT || neighbour.direction == Direction::RIGHT
+                {
+                    next_direction.x *= -1;
+                } else {
+                    next_direction.y *= -1;
+                }
+
+                // Return the new bounce direction
+                self.direction = next_direction;
+
+                self.move_next();
+
+                // Don't tell update function that we hit a void block, to avoid overriding it.
+                // We changed direction anyway.
+                if neighbour.cell.variance != CellVariance::VOID {
+                    return Some(neighbour);
+                }
+
+                None
+            }
+        }
+    }
+
+    fn check_neighborhood(&self, map: &Vec<Cell>) -> Option<Neighbour> {
+        if self.pos_y == 0 && self.direction.y == -1 {
+            return Some(Neighbour {
+                cell: map[0],
+                direction: Direction::TOP,
+                pos_x: 0,
+                pos_y: 0,
+            });
+        }
+
+        if self.pos_x == 0 && self.direction.x == -1 {
+            return Some(Neighbour {
+                cell: map[0],
+                direction: Direction::LEFT,
+                pos_x: 0,
+                pos_y: 0,
+            });
+        }
+
+        let left = (self.pos_x.checked_sub(1).unwrap_or(0), self.pos_y);
+        let right = (self.pos_x.checked_add(1).unwrap_or(0), self.pos_y);
+        let top = (self.pos_x, self.pos_y.checked_sub(1).unwrap_or(0));
+        let bottom = (self.pos_x, (self.pos_y.checked_add(1).unwrap_or(0)));
+
+        let cell_left = map.get(left.0 + left.1 * WIDTH).unwrap_or(&Cell {
+            variance: CellVariance::VOID,
+        });
+        let cell_right = map.get(right.0 + right.1 * WIDTH).unwrap_or(&Cell {
+            variance: CellVariance::VOID,
+        });
+        let cell_top = map.get(top.0 + top.1 * WIDTH).unwrap_or(&Cell {
+            variance: CellVariance::VOID,
+        });
+        let cell_bottom = map.get(bottom.0 + bottom.1 * WIDTH).unwrap_or(&Cell {
+            variance: CellVariance::VOID,
+        });
+
+        if self.obstructed_from.contains(&cell_left.variance) {
+            return Some(Neighbour {
+                cell: cell_left.clone(),
+                direction: Direction::LEFT,
+                pos_x: left.0,
+                pos_y: left.1,
+            });
+        }
+        if self.obstructed_from.contains(&cell_right.variance) {
+            return Some(Neighbour {
+                cell: cell_right.clone(),
+                direction: Direction::RIGHT,
+                pos_x: right.0,
+                pos_y: right.1,
+            });
+        }
+        if self.obstructed_from.contains(&cell_top.variance) {
+            return Some(Neighbour {
+                cell: cell_top.clone(),
+                direction: Direction::TOP,
+                pos_x: top.0,
+                pos_y: top.1,
+            });
+        }
+        if self.obstructed_from.contains(&cell_bottom.variance) {
+            return Some(Neighbour {
+                cell: cell_bottom.clone(),
+                direction: Direction::BOTTOM,
+                pos_x: bottom.0,
+                pos_y: bottom.1,
+            });
+        }
+
+        return None;
+    }
+
+    pub fn move_next(&mut self) {
+        let mov_x = self.pos_x.checked_add_signed(self.direction.x);
+        let mov_y = self.pos_y.checked_add_signed(self.direction.y);
+
+        if mov_x.is_none() || mov_y.is_none() {
+            println!("Illegal move prevented");
+        } else {
+            self.pos_x = mov_x.unwrap();
+            self.pos_y = mov_y.unwrap();
+        }
+    }
+
+    pub fn next_position(&self) -> (Option<usize>, Option<usize>) {
+        (
+            (self.pos_x.checked_add_signed(self.direction.x)),
+            (self.pos_y.checked_add_signed(self.direction.y)),
+        )
     }
 }

src/stage.rs

@@ -1,3 +1,6 @@
+use std::borrow::Borrow;
+use std::cell;
+
 use noise::utils::NoiseMapBuilder;
 use noise::utils::PlaneMapBuilder;
 use noise::BasicMulti;
@@ -7,15 +10,16 @@ use randomize::PCG32;
 
 use crate::cell::Cell;
 use crate::cell::CellVariance;
-use crate::direction::Direction;
+use crate::direction::Coord;
 use crate::npc::NPC;
+
+#[derive(Debug, Clone)]
 pub struct Stage {
     cells: Vec<Cell>,
 
     /// Used for temporary work item. Replaces `cells` once done.
     cells_dup: Vec<Cell>,
     npcs: Vec<NPC>,
-    npc_map: Vec<Option<Cell>>,
     width: usize,
     height: usize,
 }
@@ -34,7 +38,6 @@ impl Stage {
             cells: vec![Cell::default(); size],
             cells_dup: vec![Cell::default(); size],
             npcs: vec![],
-            npc_map: vec![None; size],
             width,
             height,
         }
@@ -113,10 +116,10 @@ impl Stage {
         let npc: NPC;
         match cell.variance {
             CellVariance::DAY => {
-                npc = NPC::new_day(pos_x, pos_y, Direction::new(-1, -1));
+                npc = NPC::new_day(pos_x, pos_y, Coord::new(-1, -1));
             }
             CellVariance::NIGHT => {
-                npc = NPC::new_night(pos_x, pos_y, Direction::new(-1, -1));
+                npc = NPC::new_night(pos_x, pos_y, Coord::new(-1, -1));
             }
             CellVariance::VOID => {
                 // Ignore this stupid request.
@@ -132,29 +135,28 @@ impl Stage {
     pub fn draw(&mut self, screen: &mut [u8]) {
         debug_assert_eq!(screen.len(), 4 * self.cells.len());
 
-        // Draw NPCs
-        self.npc_map.fill(None);
-        for (i, npc) in self.npcs.iter().enumerate() {
-            let map_pos = npc.pos_x + npc.pos_y * self.width;
-            // let color = match npc.walk_on {
-            //     CellVariance::DAY => [0x10, 0x41, 0x4F, 0xFF],
-            //     CellVariance::NIGHT => [0xD3, 0xE3, 0xD3, 0xFF],
-            //     _ => {
-            //         panic!("This NPC shouldn't even exist!");
-            //     }
-            // };
-
-            self.npc_map[map_pos] = Some(Cell::new(npc.obstructed_from[0]));
-        }
-
         // Draw background
-        for (i, (mut c, pix)) in self.cells.iter().zip(screen.chunks_exact_mut(4)).enumerate() {
-            let npc_cell = self.npc_map.get(i).unwrap();
-            if let Some(npc_cell) = npc_cell {
-                c = &npc_cell;
+        for (i, (c, pix)) in self
+            .cells
+            .iter()
+            .zip(screen.chunks_exact_mut(4))
+            .enumerate()
+        {
+            let mut cell: Cell = c.clone();
+
+            let mut npc_cell: Option<NPC> = None;
+            for npc in self.npcs.iter() {
+                if npc.pos_x + npc.pos_y * self.width == i {
+                    npc_cell = Some(npc.clone());
+                }
             }
 
-            let color = match c.variance {
+            // Draw NPCs
+            if let Some(npc_cell) = npc_cell {
+                cell = npc_cell.into_cell();
+            }
+
+            let color = match cell.variance {
                 CellVariance::VOID => [0x0, 0x0, 0x0, 0xFF],
                 CellVariance::DAY => [0xD3, 0xE3, 0xD3, 0xFF],
                 CellVariance::NIGHT => [0x10, 0x41, 0x4F, 0xFF],
@@ -169,35 +171,23 @@ impl Stage {
     }
 
     pub fn update(&mut self) {
-        // TODO: Flying balls
+        // Process bounce logic
         for npc in self.npcs.iter_mut() {
-            let next_pos = ((npc.pos_x as isize + npc.direction.x), (npc.pos_y as isize + npc.direction.y));
-            if next_pos.0 < 0 || next_pos.1 < 0 {
-                // TODO: Bounce
-                continue;
+            match npc.process_bounce(&self.cells_dup) {
+                Some(n) => {
+                    let c = self.cells[n.pos_x + n.pos_y * self.width];
+                    self.cells[n.pos_x + n.pos_y * self.width] = c.invert();
+                },
+                None => {}
             }
-
-            let index = next_pos.0 as usize + next_pos.1 as usize * self.width;
-            let next_cell = self.cells_dup[index];
-
-            // If our next cell would be one that we collide with.
-            if npc.obstructed_from.contains(&next_cell.variance) {
-                // TODO: Bounce
-                continue;
-            }
-
-            npc.pos_x = next_pos.0 as usize;
-            npc.pos_y = next_pos.1 as usize;
-
-            // We can move freely for now.
-            self.npc_map[index] = Some(Cell::new(npc.obstructed_from[0]));
         }
 
+        // Write current background 
         for y in 0..self.height {
             for x in 0..self.width {
                 let idx = x + y * self.width;
-                // Write into scratch_cells, since we're still reading from `self.cells`
 
+                // Write into scratch_cells, since we're still reading from `self.cells`
                 self.cells_dup[idx] = self.cells[idx];
             }
         }