Rust SDL2练习案例

案例来自于Rust Programming by Example,由于按照书籍的操作会存在一些错误，所以用此博客来记录更多的细节。

实验环境

MacOS M2: 13.5.2
Rust: 1.70.0

初始化开发环境

创建工程

cargo new tetris

添加依赖于Cargo.toml

[package]
name = "tetris"
version = "0.0.1"

[dependencies]
sdl2 = "0.34.5"

安装SDL2

brew install sdl2

配置环境变量

export RUSTFLAGS="-L /opt/homebrew/lib"

此处RUSTFLAGS环境变量的内容需要根据自己的SDL2库的安装路径来配置，由于我的库安装路径是/opt/homebrew/lib下。执行cargo build编译程序会依赖SDL的动态库；同时我也尝试了其他两种方法并没有成功

其它方法一：设置环境变量DYLD_LIBRARY_PATH

export DYLD_LIBRARY_PATH=/opt/homebrew/lib

其它方法二：在Cargo.toml中添加

[build]
rustc-link-search = ["/opt/homebrew/lib"]

基础示例代码

extern crate sdl2;

use sdl2::event::Event;
use sdl2::keyboard::Keycode;
use sdl2::pixels::Color;
use std::time::Duration;

fn main() {
    // 初始化SDL2
    let sdl_context = sdl2::init().unwrap();
    let video_subsystem = sdl_context.video().unwrap();

    // 创建窗口和画布
    let window = video_subsystem
        .window("SDL2 Window", 800, 600)
        .position_centered()
        .build()
        .unwrap();

    let mut canvas = window.into_canvas().build().expect("Failed to convert window into canvas");

    // 渲染代码
    canvas.set_draw_color(Color::RGB(255, 0, 0));
    canvas.clear();
    canvas.present();

    // 创建事件处理器
    let mut event_pump = sdl_context.event_pump().expect("Failed to get SDL event pump");

    // 主循环
    'runningloop: loop {
        for event in event_pump.poll_iter() {
            match event {
                Event::Quit { .. } | Event::KeyDown { keycode: Some(Keycode::Escape), .. } => {
                    break 'runningloop;
                }
                _ => {}
            }
        }

        // 添加延迟以控制帧率
        std::thread::sleep(Duration::new(0, 1_000_000_000u32 / 60));
    }
}

构建程序

cargo build

运行程序

cargo run

运行结果如下图：

实现过程

导入外部crate SDL2
```
extern crate sdl2;
```

初始化SDL context

let sdl_context = sdl2::init().expect("SDL initialization failed");

获取video subsystem

let video_subsystem = sdl_context.video().expect("Couldn't get SDL
       video subsystem");

创建windows

let window = video_subsystem.window("Tetris", 800, 600)
                             .position_centered()
                             .opengl()
                             .build()
                             .expect("Failed to create window");

the parameters for the window method
- title
- width
- height
.position_centered() method
- 在屏幕中间获取窗口
.opengl()
- 让SDL使用opengl渲染
.build()
- 根据前面提供的参数创建窗口
.expect()
- 处理异常

事件循环正常情况下，展示一个窗口并关闭特别快，我们需要添加时间循环确保窗口一直在运行。

导入必要相关的库

use sdl2::event::Event;
use sdl2::keyboard::Keycode;

use std::thread::sleep;
use std::time::Duration;

获取时间循环管理器

let mut event_pump = sdl_context.event_pump().expect("Failed to
        get SDL event pump");

创建无限循环循环事件

'running: loop {
     for event in event_pump.poll_iter() {
         match event {
             Event::Quit { .. } |
             Event::KeyDown { keycode: Some(Keycode::Escape), .. } => {
                 break 'running // We "break" the infinite loop.
             },
             _ => {} 
         }
     }
     sleep(Duration::new(0, 1_000_000_000u32 / 60));
}

running是一个循环跳出的标签(label) 收到一个quit event或者按Esc键，程序退出

画布(Canvas)

当我们有了一个窗口(window)时，我们需要获取(get)窗口的画布(window's canvas)

let mut canvas = window.into_canvas()
                 .target_texture()
                 .present_vsync()
                 .build()
                 .expect("Couldn't get window's canvas");

以上代码的简单说明：

into_canvas: 将窗口(window)转换为画布(canvas)，以便我们可以轻松操作它
target_texture: 激活纹理渲染支持
present_vsync: 允许v-sync(竖直同步操作)限制
build: 应用前面设置的参数创建画布(canvas)

纹理(Texture)

当我们有了一个窗口的画布时，我们可以创建纹理，粘贴(paste onto)在其上。获取(get)一个纹理创造器(texture creator)

添加包含的结构

use sdl2::render::{Canvas, Texture, TextureCreator};

获取纹理创造器

let texture_creator: TextureCreator<_> = canvas.texture_creator();

创建矩形

首先创建一个常量确定矩形的尺寸，然后使用纹理创造器创建一个矩形的纹理

设置矩形矩形的尺寸

const TEXTURE_SIZE: u32 = 32; // 矩形的尺寸大小

使用纹理创造器创建矩形

const TEXTURE_SIZE: u32 = 32; // 矩形的尺寸大小
let mut square_texture: Texture =
   texture_creator.create_texture_target(None, TEXTURE_SIZE,
     TEXTURE_SIZE)
   .expect("Failed to create a texture");

设置颜色

要为纹理设置颜色，需要引入颜色模块的结构，然后使用画布设置纹理的颜色，颜色绘制完成后需要清空纹理；

引入颜色结构
```
use sdl2::pixels::Color;
```

使用画布设置矩形纹理的颜色

canvas.with_texture_canvas(&mut square_texture, |texture| {
  texture.set_draw_color(Color::RGB(0, 255, 0));
  texture.clear();
})

代码的简单说明:

为了更新窗口的渲染内容，我们需要在将代码包含在main loop(and after the event loop). clear()纹理，以至于它被填充绿色

将窗口填充红色

canvas.set_draw_color(Color::RGB(255, 0, 0));
canvas.clear();

将纹理拷贝到窗口中

canvas.copy(&square_texture, None, Rect::new(0, 0, TEXTURE_SIZE, TEXTURE_SIZE))
      .expect("Couldn't copy texture into window");

最后更新窗口的展示
```
canvas.present();
```

在红色画布上绘制绿色矩形的完整代码

代码如下：

extern crate sdl2;

use sdl2::event::Event;
use sdl2::keyboard::Keycode;
use sdl2::pixels::Color;
use sdl2::render::{Texture, TextureCreator};
use sdl2::rect::Rect;
use std::time::Duration;

fn main() {
     // 初始化SDL2
     let sdl_context = sdl2::init().expect("SDL initialization failed");
     let video_subsystem = sdl_context.video().expect("Couldn't get SDL video subsystem");

     // 创建窗口和画布
     let window = video_subsystem
         .window("Tetris", 800, 600)
         .position_centered()
         .build()
         .expect("Failed to create window");

     let mut canvas = window.into_canvas()
         .target_texture()
         .present_vsync()
         .build()
         .expect("Couldn't get window's canvas");

     let texture_creator: TextureCreator<_> = canvas.texture_creator();
     const TEXTURE_SIZE: u32 = 32;

     // create a texture with a 32*32 size
     let mut square_texture: Texture = texture_creator.create_texture_target(None, TEXTURE_SIZE, TEXTURE_SIZE)
         .expect("Failed to create a texture");

     // use the canvas to draw into our square texture.
     canvas.with_texture_canvas(&mut square_texture, |texture| {
         // set the draw color to green
         texture.set_draw_color(Color::RGB(0, 255, 0));
         texture.clear();
     }).expect("Failed to clear a texture");

     // 创建事件处理器
     let mut event_pump = sdl_context.event_pump().expect("Failed to get SDL event pump");

     // 主循环
     'runningloop: loop {
         for event in event_pump.poll_iter() {
             match event {
                 Event::Quit { .. } | Event::KeyDown { keycode: Some(Keycode::Escape), .. } => {
                     break 'runningloop;
                 }
                 _ => {}
             }
         }

         // We set fulfill our window with red
         canvas.set_draw_color(Color::RGB(255, 0, 0));
         // We draw it
         canvas.clear();
         // Copy our texture into the window
         canvas.copy(&square_texture, None, Rect::new(0, 0, TEXTURE_SIZE, TEXTURE_SIZE))
             .expect("Couldn't copy texture into window");
         canvas.present();

         // 添加延迟以控制帧率
         std::thread::sleep(Duration::new(0, 1_000_000_000u32 / 60));
     }
}

代码执行结果如下图所示: