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一个简单的绘画程序。

Cargo.toml 启用了与 DOM、事件和 2D 画布交互所需的特性。

[package]
name = "wasm-bindgen-paint"
version = "0.1.0"
authors = ["The wasm-bindgen Developers"]
edition = "2018"
rust-version = "1.57"

[lib]
crate-type = ["cdylib"]

[dependencies]
js-sys = "0.3.69"
wasm-bindgen = "0.2.92"

[dependencies.web-sys]
version = "0.3.4"
features = [
  'CanvasRenderingContext2d',
  'CssStyleDeclaration',
  'Document',
  'Element',
  'EventTarget',
  'HtmlCanvasElement',
  'HtmlElement',
  'MouseEvent',
  'Node',
  'Window',
]

创建 <canvas> 元素，对其应用 CSS 样式，将其添加到文档中，获取 2D 渲染上下文并添加鼠标事件监听器。

# #![allow(unused_variables)]
#fn main() {
use std::cell::Cell;
use std::rc::Rc;
use wasm_bindgen::prelude::*;

#[wasm_bindgen(start)]
fn start() -> Result<(), JsValue> {
    let document = web_sys::window().unwrap().document().unwrap();
    let canvas = document
        .create_element("canvas")?
        .dyn_into::<web_sys::HtmlCanvasElement>()?;
    document.body().unwrap().append_child(&canvas)?;
    canvas.set_width(640);
    canvas.set_height(480);
    canvas.style().set_property("border", "solid")?;
    let context = canvas
        .get_context("2d")?
        .unwrap()
        .dyn_into::<web_sys::CanvasRenderingContext2d>()?;
    let context = Rc::new(context);
    let pressed = Rc::new(Cell::new(false));
    {
        let context = context.clone();
        let pressed = pressed.clone();
        let closure = Closure::<dyn FnMut(_)>::new(move |event: web_sys::MouseEvent| {
            context.begin_path();
            context.move_to(event.offset_x() as f64, event.offset_y() as f64);
            pressed.set(true);
        });
        canvas.add_event_listener_with_callback("mousedown", closure.as_ref().unchecked_ref())?;
        closure.forget();
    }
    {
        let context = context.clone();
        let pressed = pressed.clone();
        let closure = Closure::<dyn FnMut(_)>::new(move |event: web_sys::MouseEvent| {
            if pressed.get() {
                context.line_to(event.offset_x() as f64, event.offset_y() as f64);
                context.stroke();
                context.begin_path();
                context.move_to(event.offset_x() as f64, event.offset_y() as f64);
            }
        });
        canvas.add_event_listener_with_callback("mousemove", closure.as_ref().unchecked_ref())?;
        closure.forget();
    }
    {
        let closure = Closure::<dyn FnMut(_)>::new(move |event: web_sys::MouseEvent| {
            pressed.set(false);
            context.line_to(event.offset_x() as f64, event.offset_y() as f64);
            context.stroke();
        });
        canvas.add_event_listener_with_callback("mouseup", closure.as_ref().unchecked_ref())?;
        closure.forget();
    }

    Ok(())
}

#}