推动箱子

在上一章中，我们让玩家可以移动，但他可以穿过墙壁和箱子，并没有真正与环境交互。在本节中，我们将为玩家的移动添加一些更智能的逻辑。

移动组件

首先，我们需要让代码稍微更通用一些。如果你还记得上一章，我们是通过操作玩家来决定如何移动他们的，但我们也需要移动箱子。此外，未来我们可能会引入其他可移动类型的对象，因此我们需要考虑到这一点。按照真正的 ECS（实体-组件-系统） 精神，我们将使用标记组件来区分哪些实体是可移动的，哪些不是。例如，玩家和箱子是可移动的，而墙是不可移动的。箱子放置点在这里无关紧要，因为它们不会移动，但它们也不应该影响玩家或箱子的移动，因此箱子放置点不会具有这些组件中的任何一个。

以下是我们的两个新组件：

#![allow(unused)]
fn main() {
pub struct Movable;

pub struct Immovable;
}

接下来，我们将：

• 为玩家和箱子添加 with(Movable)
• 为墙添加 with(Immovable)
• 对地板和箱子放置点不做任何操作（如前所述，它们不应成为我们的移动/碰撞系统的一部分，因为它们对移动没有影响）

#![allow(unused)]
fn main() {
pub fn create_wall(world: &mut World, position: Position) -> Entity {
    world.spawn((
        Position { z: 10, ..position },
        Renderable {
            path: "/images/wall.png".to_string(),
        },
        Wall {},
        Immovable {},
    ))
}
pub fn create_floor(world: &mut World, position: Position) -> Entity {
    world.spawn((
        Position { z: 5, ..position },
        Renderable {
            path: "/images/floor.png".to_string(),
        },
    ))
}

pub fn create_box(world: &mut World, position: Position) -> Entity {
    world.spawn((
        Position { z: 10, ..position },
        Renderable {
            path: "/images/box.png".to_string(),
        },
        Box {},
        Movable {},
    ))
}

pub fn create_box_spot(world: &mut World, position: Position) -> Entity {
    world.spawn((
        Position { z: 9, ..position },
        Renderable {
            path: "/images/box_spot.png".to_string(),
        },
        BoxSpot {},
    ))
}

pub fn create_player(world: &mut World, position: Position) -> Entity {
    world.spawn((
        Position { z: 10, ..position },
        Renderable {
            path: "/images/player.png".to_string(),
        },
        Player {},
        Movable {},
    ))
}
}

移动需求

现在让我们思考一些示例来说明移动的需求。这将帮助我们理解如何修改输入系统的实现以正确使用 Movable 和 Immovable。

场景：

1. (player, floor) 并按下 RIGHT -> 玩家应该向右移动
2. (player, wall) 并按下 RIGHT -> 玩家不应向右移动
3. (player, box, floor) 并按下 RIGHT -> 玩家应该向右移动，箱子也应该向右移动
4. (player, box, wall) 并按下 RIGHT -> 没有任何东西应该移动
5. (player, box, box, floor) 并按下 RIGHT -> 玩家、箱子1 和箱子2 应该都向右移动一格
6. (player, box, box, wall) 并按下 RIGHT -> 没有任何东西应该移动

基于这些场景，我们可以做出以下观察：

• 碰撞/移动检测应该一次性处理所有涉及的对象——例如，对于场景 6，如果我们逐个处理，每次处理一个对象，我们会先移动玩家，再移动第一个箱子，当我们处理第二个箱子时发现无法移动，此时需要回滚所有的移动操作，这是不可行的。因此，对于每个输入，我们必须找出所有涉及的对象，并整体判断该动作是否可行。
• 一条包含空位的可移动链可以移动（空位在此表示既非可移动也非不可移动的东西）
• 一条包含不可移动位置的可移动链不能移动
• 尽管所有示例都是向右移动，这些规则应该可以推广到任何方向，按键仅仅影响我们如何找到链条

因此，基于这些规则，让我们开始实现这个逻辑。以下是我们需要的逻辑模块的一些初步想法：

1. 找到所有可移动和不可移动的实体 - 这样我们可以判断它们是否受到移动的影响
2. 根据按键确定移动方向 - 我们在上一节已经大致解决了这个问题，基本上是一些基于按键枚举的 +1/-1 操作
3. 遍历从玩家到地图边缘的所有位置，根据方向确定轴线——例如，如果按下右键，我们需要从 player.x 遍历到 map_width，如果按下上键，我们需要从 0 遍历到 player.y
4. 对于序列中的每个格子 我们需要：
   • 如果格子是可移动的，继续并记住这个格子
   • 如果格子不可移动，停止并不移动任何东西
   • 如果格子既不可移动也不可移动，移动我们记住的所有格子

以下是输入系统的新实现，有点长，但希望能理解。

#![allow(unused)]
fn main() {
fn run_input(world: &World, context: &mut Context) {
    let mut to_move: Vec<(Entity, KeyCode)> = Vec::new();

    // get all the movables and immovables
    let mov: HashMap<(u8, u8), Entity> = world
        .query::<(&Position, &Movable)>()
        .iter()
        .map(|t| ((t.1 .0.x, t.1 .0.y), t.0))
        .collect::<HashMap<_, _>>();
    let immov: HashMap<(u8, u8), Entity> = world
        .query::<(&Position, &Immovable)>()
        .iter()
        .map(|t| ((t.1 .0.x, t.1 .0.y), t.0))
        .collect::<HashMap<_, _>>();

    for (_, (position, _player)) in world.query::<(&mut Position, &Player)>().iter() {
        if context.keyboard.is_key_repeated() {
            continue;
        }

        // Now iterate through current position to the end of the map
        // on the correct axis and check what needs to move.
        let key = if context.keyboard.is_key_pressed(KeyCode::Up) {
            KeyCode::Up
        } else if context.keyboard.is_key_pressed(KeyCode::Down) {
            KeyCode::Down
        } else if context.keyboard.is_key_pressed(KeyCode::Left) {
            KeyCode::Left
        } else if context.keyboard.is_key_pressed(KeyCode::Right) {
            KeyCode::Right
        } else {
            continue;
        };

        let (start, end, is_x) = match key {
            KeyCode::Up => (position.y, 0, false),
            KeyCode::Down => (position.y, MAP_HEIGHT - 1, false),
            KeyCode::Left => (position.x, 0, true),
            KeyCode::Right => (position.x, MAP_WIDTH - 1, true),
            _ => continue,
        };

        let range = if start < end {
            (start..=end).collect::<Vec<_>>()
        } else {
            (end..=start).rev().collect::<Vec<_>>()
        };

        for x_or_y in range {
            let pos = if is_x {
                (x_or_y, position.y)
            } else {
                (position.x, x_or_y)
            };

            // find a movable
            // if it exists, we try to move it and continue
            // if it doesn't exist, we continue and try to find an immovable instead
            match mov.get(&pos) {
                Some(entity) => to_move.push((*entity, key)),
                None => {
                    // find an immovable
                    // if it exists, we need to stop and not move anything
                    // if it doesn't exist, we stop because we found a gap
                    match immov.get(&pos) {
                        Some(_id) => to_move.clear(),
                        None => break,
                    }
                }
            }
        }
    }

    // Now actually move what needs to be moved
    for (entity, key) in to_move {
        let mut position = world.get::<&mut Position>(entity).unwrap();

        match key {
            KeyCode::Up => position.y -= 1,
            KeyCode::Down => position.y += 1,
            KeyCode::Left => position.x -= 1,
            KeyCode::Right => position.x += 1,
            _ => (),
        }
    }
}
}

现在运行代码，你会发现它真的有效了！我们不能再穿过墙壁，可以推动箱子，当箱子碰到墙时会停下。

以下是完整代码。

/* ANCHOR: all */
// Rust sokoban
// main.rs

use ggez::{
    conf, event,
    graphics::{self, DrawParam, Image},
    input::keyboard::KeyCode,
    Context, GameResult,
};
use glam::Vec2;
use hecs::{Entity, World};

use std::collections::HashMap;
use std::path;

const TILE_WIDTH: f32 = 32.0;
const MAP_WIDTH: u8 = 8;
const MAP_HEIGHT: u8 = 9;

// ANCHOR: components
#[derive(Clone, Copy, Eq, Hash, PartialEq)]
pub struct Position {
    x: u8,
    y: u8,
    z: u8,
}

pub struct Renderable {
    path: String,
}

pub struct Wall {}

pub struct Player {}

pub struct Box {}

pub struct BoxSpot {}

// ANCHOR: components_movement
pub struct Movable;

pub struct Immovable;
// ANCHOR_END: components_movement

// ANCHOR_END: components

// ANCHOR: game
// This struct will hold all our game state
// For now there is nothing to be held, but we'll add
// things shortly.
struct Game {
    world: World,
}
// ANCHOR_END: game

// ANCHOR: init
// Initialize the level// Initialize the level
pub fn initialize_level(world: &mut World) {
    const MAP: &str = "
    N N W W W W W W
    W W W . . . . W
    W . . . B . . W
    W . . . . . . W 
    W . P . . . . W
    W . . . . . . W
    W . . S . . . W
    W . . . . . . W
    W W W W W W W W
    ";

    load_map(world, MAP.to_string());
}

pub fn load_map(world: &mut World, map_string: String) {
    // read all lines
    let rows: Vec<&str> = map_string.trim().split('\n').map(|x| x.trim()).collect();

    for (y, row) in rows.iter().enumerate() {
        let columns: Vec<&str> = row.split(' ').collect();

        for (x, column) in columns.iter().enumerate() {
            // Create the position at which to create something on the map
            let position = Position {
                x: x as u8,
                y: y as u8,
                z: 0, // we will get the z from the factory functions
            };

            // Figure out what object we should create
            match *column {
                "." => {
                    create_floor(world, position);
                }
                "W" => {
                    create_floor(world, position);
                    create_wall(world, position);
                }
                "P" => {
                    create_floor(world, position);
                    create_player(world, position);
                }
                "B" => {
                    create_floor(world, position);
                    create_box(world, position);
                }
                "S" => {
                    create_floor(world, position);
                    create_box_spot(world, position);
                }
                "N" => (),
                c => panic!("unrecognized map item {}", c),
            }
        }
    }
}
// ANCHOR_END: init

// ANCHOR: handler
impl event::EventHandler<ggez::GameError> for Game {
    fn update(&mut self, context: &mut Context) -> GameResult {
        // Run input system
        {
            run_input(&self.world, context);
        }

        Ok(())
    }

    fn draw(&mut self, context: &mut Context) -> GameResult {
        // Render game entities
        {
            run_rendering(&self.world, context);
        }

        Ok(())
    }
}
// ANCHOR_END: handler

// ANCHOR: entities
pub fn create_wall(world: &mut World, position: Position) -> Entity {
    world.spawn((
        Position { z: 10, ..position },
        Renderable {
            path: "/images/wall.png".to_string(),
        },
        Wall {},
        Immovable {},
    ))
}
pub fn create_floor(world: &mut World, position: Position) -> Entity {
    world.spawn((
        Position { z: 5, ..position },
        Renderable {
            path: "/images/floor.png".to_string(),
        },
    ))
}

pub fn create_box(world: &mut World, position: Position) -> Entity {
    world.spawn((
        Position { z: 10, ..position },
        Renderable {
            path: "/images/box.png".to_string(),
        },
        Box {},
        Movable {},
    ))
}

pub fn create_box_spot(world: &mut World, position: Position) -> Entity {
    world.spawn((
        Position { z: 9, ..position },
        Renderable {
            path: "/images/box_spot.png".to_string(),
        },
        BoxSpot {},
    ))
}

pub fn create_player(world: &mut World, position: Position) -> Entity {
    world.spawn((
        Position { z: 10, ..position },
        Renderable {
            path: "/images/player.png".to_string(),
        },
        Player {},
        Movable {},
    ))
}
// ANCHOR_END: entities

// ANCHOR: rendering_system
fn run_rendering(world: &World, context: &mut Context) {
    // Clearing the screen (this gives us the background colour)
    let mut canvas =
        graphics::Canvas::from_frame(context, graphics::Color::from([0.95, 0.95, 0.95, 1.0]));

    // Get all the renderables with their positions and sort by the position z
    // This will allow us to have entities layered visually.
    let mut query = world.query::<(&Position, &Renderable)>();
    let mut rendering_data: Vec<(Entity, (&Position, &Renderable))> = query.into_iter().collect();
    rendering_data.sort_by_key(|&k| k.1 .0.z);

    // Iterate through all pairs of positions & renderables, load the image
    // and draw it at the specified position.
    for (_, (position, renderable)) in rendering_data.iter() {
        // Load the image
        let image = Image::from_path(context, renderable.path.clone()).unwrap();
        let x = position.x as f32 * TILE_WIDTH;
        let y = position.y as f32 * TILE_WIDTH;

        // draw
        let draw_params = DrawParam::new().dest(Vec2::new(x, y));
        canvas.draw(&image, draw_params);
    }

    // Finally, present the canvas, this will actually display everything
    // on the screen.
    canvas.finish(context).expect("expected to present");
}
// ANCHOR_END: rendering_system

// ANCHOR: input_system
fn run_input(world: &World, context: &mut Context) {
    let mut to_move: Vec<(Entity, KeyCode)> = Vec::new();

    // get all the movables and immovables
    let mov: HashMap<(u8, u8), Entity> = world
        .query::<(&Position, &Movable)>()
        .iter()
        .map(|t| ((t.1 .0.x, t.1 .0.y), t.0))
        .collect::<HashMap<_, _>>();
    let immov: HashMap<(u8, u8), Entity> = world
        .query::<(&Position, &Immovable)>()
        .iter()
        .map(|t| ((t.1 .0.x, t.1 .0.y), t.0))
        .collect::<HashMap<_, _>>();

    for (_, (position, _player)) in world.query::<(&mut Position, &Player)>().iter() {
        if context.keyboard.is_key_repeated() {
            continue;
        }

        // Now iterate through current position to the end of the map
        // on the correct axis and check what needs to move.
        let key = if context.keyboard.is_key_pressed(KeyCode::Up) {
            KeyCode::Up
        } else if context.keyboard.is_key_pressed(KeyCode::Down) {
            KeyCode::Down
        } else if context.keyboard.is_key_pressed(KeyCode::Left) {
            KeyCode::Left
        } else if context.keyboard.is_key_pressed(KeyCode::Right) {
            KeyCode::Right
        } else {
            continue;
        };

        let (start, end, is_x) = match key {
            KeyCode::Up => (position.y, 0, false),
            KeyCode::Down => (position.y, MAP_HEIGHT - 1, false),
            KeyCode::Left => (position.x, 0, true),
            KeyCode::Right => (position.x, MAP_WIDTH - 1, true),
            _ => continue,
        };

        let range = if start < end {
            (start..=end).collect::<Vec<_>>()
        } else {
            (end..=start).rev().collect::<Vec<_>>()
        };

        for x_or_y in range {
            let pos = if is_x {
                (x_or_y, position.y)
            } else {
                (position.x, x_or_y)
            };

            // find a movable
            // if it exists, we try to move it and continue
            // if it doesn't exist, we continue and try to find an immovable instead
            match mov.get(&pos) {
                Some(entity) => to_move.push((*entity, key)),
                None => {
                    // find an immovable
                    // if it exists, we need to stop and not move anything
                    // if it doesn't exist, we stop because we found a gap
                    match immov.get(&pos) {
                        Some(_id) => to_move.clear(),
                        None => break,
                    }
                }
            }
        }
    }

    // Now actually move what needs to be moved
    for (entity, key) in to_move {
        let mut position = world.get::<&mut Position>(entity).unwrap();

        match key {
            KeyCode::Up => position.y -= 1,
            KeyCode::Down => position.y += 1,
            KeyCode::Left => position.x -= 1,
            KeyCode::Right => position.x += 1,
            _ => (),
        }
    }
}
// ANCHOR_END: input_system

// ANCHOR: main
pub fn main() -> GameResult {
    let mut world = World::new();
    initialize_level(&mut world);

    // Create a game context and event loop
    let context_builder = ggez::ContextBuilder::new("rust_sokoban", "sokoban")
        .window_setup(conf::WindowSetup::default().title("Rust Sokoban!"))
        .window_mode(conf::WindowMode::default().dimensions(800.0, 600.0))
        .add_resource_path(path::PathBuf::from("./resources"));

    let (context, event_loop) = context_builder.build()?;

    // Create the game state
    let game = Game { world };
    // Run the main event loop
    event::run(context, event_loop, game)
}
// ANCHOR_END: main

/* ANCHOR_END: all */

CODELINK: 你可以在 这里 查看本示例的完整代码。