Add visibility simulation

We need to be able to spawn entities from the generator function, both
as level props and as enemies; the previous API makes this impossible,
so I'm working on restructuring it. Not too happy with it yet, still
needs more work.

src/level.rs

@@ -1,22 +1,35 @@
 use std::fmt::Display;
 
 use pancurses::Window;
+use rand::Rng;
+use specs::prelude::*;
 
-use crate::rooms;
+use crate::{
+    components::{CharRender, Position},
+    rooms,
+};
 
 /// The size of a dungeon level, in tiles.
 pub const LEVEL_SIZE: (usize, usize) = (80, 24);
 
 /// A single level of the dungeon.
+#[derive(Clone)]
 pub struct DungeonLevel {
     /// The tiles at every position in the level.
     tiles: [[DungeonTile; LEVEL_SIZE.0]; LEVEL_SIZE.1],
 
+    /// The locations of the level's exits.
+    exits: LevelExits,
+}
+
+/// The entrances and exits from a level.
+#[derive(Clone)]
+pub struct LevelExits {
     /// The location of each of the up-staircases.
-    upstairs: Vec<(i32, i32)>,
+    pub upstairs: Vec<(i32, i32)>,
 
     /// The location of each of the down-staircases.
-    downstairs: Vec<(i32, i32)>,
+    pub downstairs: Vec<(i32, i32)>,
 }
 
 /// The smallest measurable independent location in the dungeon,
@@ -49,32 +62,57 @@ impl DungeonTile {
 }
 
 impl DungeonLevel {
-    /// Creates a new level in a branch that has the given
-    /// configuration.
-    pub fn new() -> Self {
-        rooms::generate_level(100, &mut rand::thread_rng(), 1, 1)
-    }
-
     /// Creates a new level with the given set of tiles, upstairs, and
     /// downstairs.
-    pub fn from_raw_parts(
+    pub fn new(
         tiles: [[DungeonTile; LEVEL_SIZE.0]; LEVEL_SIZE.1],
         upstairs: Vec<(i32, i32)>,
         downstairs: Vec<(i32, i32)>,
     ) -> Self {
         Self {
             tiles,
-            upstairs,
-            downstairs,
+            exits: LevelExits {
+                upstairs,
+                downstairs,
+            },
         }
     }
 
-    /// Draws a level on the display window.
-    pub fn draw(&self, win: &Window) {
+    /// Creates a new level and registers it with the given world.
+    pub fn generate_level(world: &mut World, rng: &mut impl Rng) -> LevelExits {
+        let level = rooms::generate_level(100, rng, 1, 1);
+        world.insert(level.clone()); // inefficient but whatever
+
+        // Spawn some zombies in the world.
+        for _ in 0..20 {
+            let (x, y) = (
+                rng.gen_range(0..LEVEL_SIZE.0 as _),
+                rng.gen_range(0..LEVEL_SIZE.1 as _),
+            );
+            if level.tile(x, y).is_navigable() {
+                world
+                    .create_entity()
+                    .with(Position { x, y })
+                    .with(CharRender { glyph: 'Z' })
+                    .build();
+            }
+        }
+
+        level.exits
+    }
+
+    /// Draws a level on the display window. Draws only the cells for
+    /// which `filter` returns true; use `|_| true` to draw the whole
+    /// level.
+    pub fn draw(&self, win: &Window, filter: impl Fn((i32, i32)) -> bool) {
         for y in 0..LEVEL_SIZE.1 {
             win.mv(y as _, 0);
             for x in 0..LEVEL_SIZE.0 {
-                win.addch(self.render_tile(x, y));
+                win.addch(if filter((x as _, y as _)) {
+                    self.render_tile(x, y)
+                } else {
+                    ' '
+                });
             }
         }
     }
@@ -130,16 +168,6 @@ impl DungeonLevel {
     pub fn tile(&self, x: i32, y: i32) -> &DungeonTile {
         &self.tiles[y as usize][x as usize]
     }
-
-    /// Gets the list of up-stairs.
-    pub fn upstairs(&self) -> &[(i32, i32)] {
-        &self.upstairs
-    }
-
-    /// Gets the list of down-stairs.
-    pub fn downstairs(&self) -> &[(i32, i32)] {
-        &self.downstairs
-    }
 }
 
 impl Display for DungeonLevel {

src/main.rs

@@ -5,6 +5,7 @@ use level::DungeonLevel;
 
 use pancurses::{endwin, initscr, noecho, Window};
 use player::player_turn;
+use rand::thread_rng;
 use specs::prelude::*;
 use systems::{MobSystem, TimeSystem};
 
@@ -14,14 +15,15 @@ mod player;
 mod rooms;
 mod systems;
 mod util;
+mod visibility;
 
 fn main() {
     let mut world = World::new();
 
     register_all(&mut world);
 
-    let level = DungeonLevel::new();
-    let spawn_pos = level.upstairs()[0];
+    let level = DungeonLevel::generate_level(&mut world, &mut thread_rng());
+    let spawn_pos = level.upstairs[0];
 
     world.insert(level);
 

src/player.rs

@@ -5,8 +5,9 @@ use specs::prelude::*;
 
 use crate::{
     components::{CharRender, MobAction, Mobile, Player, Position},
-    level::{DungeonLevel, DungeonTile},
+    level::DungeonLevel,
     quit,
+    visibility::{visible, CellVisibility, Lighting},
 };
 
 /// Runs a player turn on the ECS, using the given `screen` for input
@@ -85,11 +86,32 @@ fn possible(ecs: &World, action: &MobAction) -> bool {
 
 /// Renders the state of the world onto the screen.
 fn render_screen(ecs: &mut World, screen: &mut Window) {
-    // screen.clear();
+    // Calculate the player's position.
+    let plrs = ecs.read_storage::<Player>();
+    let pos = ecs.read_storage::<Position>();
+    let (_plr, player_pos) = (&plrs, &pos)
+        .join()
+        .next()
+        .expect("Player must have a position");
 
     // Draw the base level.
     let level = ecs.fetch::<DungeonLevel>();
-    level.draw(screen);
+    level.draw(screen, |cell| {
+        visible(
+            (player_pos.x, player_pos.y),
+            cell,
+            Some(10),
+            |(x, y)| {
+                if level.tile(x, y).is_navigable() {
+                    CellVisibility::Transparent
+                } else {
+                    CellVisibility::Blocking
+                }
+            },
+            // Level is fully lit for now.
+            |(_x, _y)| Lighting::Lit,
+        )
+    });
 
     // Draw all renderable entities.
     let renderables = ecs.read_storage::<CharRender>();
@@ -98,8 +120,8 @@ fn render_screen(ecs: &mut World, screen: &mut Window) {
         screen.mvaddch(pos.y as _, pos.x as _, render.glyph);
     }
 
-    // Leave the cursor at the lower-left.
-    screen.mv(0, 0);
+    // Leave the cursor on the player's position.
+    screen.mv(player_pos.y, player_pos.x);
 
     screen.refresh();
 }

src/rooms.rs

@@ -93,7 +93,7 @@ pub fn generate_level(
         *slot = value;
     }
 
-    DungeonLevel::from_raw_parts(data, upstairs, downstairs)
+    DungeonLevel::new(data, upstairs, downstairs)
 }
 
 /// The bounding box of a room.

src/visibility.rs

@@ -0,0 +1,89 @@
+//! Code for determining which cells the player and monsters can see.
+
+/// The light transmission properties of a cell in the world.
+#[derive(Debug, PartialEq)]
+pub enum CellVisibility {
+    /// This cell allows light to pass through: monsters can see
+    /// through this cell as if it is air.
+    Transparent,
+
+    /// This cell blocks all light.
+    Blocking,
+}
+
+/// How well-lit a cell is.
+#[derive(Debug, PartialEq)]
+pub enum Lighting {
+    /// Monsters can only see in this cell if the cell is immediately
+    /// adjacent to the monster.
+    Dark,
+
+    /// Monsters can see in this cell from far away.
+    Lit,
+}
+
+/// Calculates whether a monster standing at `origin` can see the
+/// contents of cell `cell`. We assume the monster can see `radius`
+/// cells away at best (None for unlimited range), that `cell_map`
+/// represents whether a cell transmits light, and that `light_map`
+/// represents how well-lit a cell is.
+pub fn visible(
+    origin: (i32, i32),
+    cell: (i32, i32),
+    radius: Option<i32>,
+    cell_map: impl Fn((i32, i32)) -> CellVisibility,
+    light_map: impl Fn((i32, i32)) -> Lighting,
+) -> bool {
+    let dx = cell.0 - origin.0;
+    let dy = cell.1 - origin.1;
+
+    radius
+        .map(|radius| dx * dx + dy * dy < radius * radius)
+        .unwrap_or(true)
+        && (light_map(cell) == Lighting::Lit)
+        && (line(origin, cell).all(|tile| cell_map(tile) == CellVisibility::Transparent))
+}
+
+/// Constructs an iterator over the cells in a straight line from
+/// `start` to `end`. The line will include `start`, but not `end`.
+fn line(start: (i32, i32), end: (i32, i32)) -> Box<dyn Iterator<Item = (i32, i32)>> {
+    // We could use a dedicated iterator type here eventually and
+    // avoid the `Box` allocations, but I'm gonna assume it's not a
+    // significant problem until proven otherwise.
+
+    let dx = end.0 - start.0;
+    let dy = end.1 - start.1;
+
+    // Transform the world so we're working from left to right, with
+    // slope magnitude less than 1.
+    if dx.abs() < dy.abs() {
+        Box::new(line((start.1, start.0), (end.1, end.0)).map(|(x, y)| (y, x)))
+    } else if dx < 0 {
+        Box::new(line((-start.0, start.1), (-end.0, end.1)).map(|(x, y)| (-x, y)))
+    } else {
+        // Move the destination over by 0.5 cells on each axis, to
+        // navigate to the corner rather than the center of the target
+        // cell. It's weird but it makes things work way better.
+        let dx = dx as f64 - 0.5;
+        let dy = if dy > 0 {
+            dy as f64 - 0.5
+        } else if dy < 0 {
+            dy as f64 + 0.5
+        } else {
+            dy as f64
+        };
+
+        // Now use float math to step along the line, one cell at a
+        // time.
+        let slope = dy as f64 / dx as f64;
+        Box::new(
+            std::iter::successors(Some((start.0, start.1 as f64)), move |&(x, y)| {
+                Some((x + 1, y + slope))
+            })
+            // Add 0.5 here to round to nearest rather than rounding
+            // towards zero (eliminates some bias).
+            .map(|(x, y)| (x, (y + 0.5) as i32))
+            .take_while(move |(x, _y)| x < &end.0),
+        )
+    }
+}