Canvaskit快速入门教程

下面是“Canvaskit快速入门教程”的详细攻略：

1. 什么是Canvaskit

Canvaskit是Google公司开发的一个用于绘制2D图像的轻量级渲染引擎，基于Skia图形库实现，可以在各种平台上实现高性能的绘制和渲染。

2. Canvaskit的基本用法

2.1 Canvaskit的安装

Canvaskit可以直接通过npm或者yarn来进行安装。在安装Canvaskit之前，需要先安装node.js和yarn。

# 使用 npm 安装 Canvaskit
npm install canvaskit

# 或者使用 yarn 安装 Canvaskit
yarn add canvaskit

2.2 使用Canvaskit绘图

通过以下代码可以创建一个Canvas元素，并将其添加到DOM中：

const { html } = require('lit-html');
const { CanvasKit } = require('canvaskit-wasm');
const canvasKit = await CanvasKit.initCanvasKit();

const width = 400;
const height = 400;
const canvas = canvasKit.MakeCanvas(width, height);

const container = document.getElementById('container');
container.appendChild(html`<canvas width="${width}" height="${height}">`);

可以通过以下方式绘制一个矩形：

const paint = new canvasKit.Paint();

paint.setStyle(canvasKit.PaintStyle.Fill);
paint.setColor(canvasKit.makeColor(255, 0, 0, 1)); // 红色
canvas.drawRect(canvasKit.makeRect(0, 0, 100, 100), paint);

我们还可以绘制一个带有文本的矩形：

paint.setColor(canvasKit.makeColor(0, 255, 0, 1)); // 绿色
paint.setTextSize(24);
paint.setAntiAlias(true);
canvasKit.Canvas.drawText(canvas, "Hello, CanvasKit!", 20, 50, paint);

2.3 示例一：绘制棋盘

下面以一个简单的示例，来演示Canvaskit的使用。

const ROW = 5;
const COL = 5;
const MOVE = 10;
const BORDER = 2;
const cellSize = 40;

const drawChessBoard = (canvas, canvasKit) => {
    const paint = new canvasKit.Paint();
    paint.setStyle(canvasKit.PaintStyle.Stroke);
    paint.setStrokeWidth(BORDER);
    paint.setColor(canvasKit.makeColor(0, 0, 0, 1));

    for (let i = 0; i <= ROW; i++) {
        canvas.drawLine(i * cellSize + MOVE, MOVE, i * cellSize + MOVE, cellSize * ROW + MOVE, paint);
        canvas.drawLine(MOVE, i * cellSize + MOVE, cellSize * ROW + MOVE, i * cellSize + MOVE, paint);
    }
};

const canvasKit = await CanvasKit.initCanvasKit();
const canvas = canvasKit.MakeCanvas(cellSize * ROW + 2 * MOVE, cellSize * COL + 2 * MOVE);

drawChessBoard(canvas, canvasKit);

const container = document.getElementById('container');
container.appendChild(html`<canvas width="${cellSize * ROW + 2 * MOVE}" height="${cellSize * COL + 2 * MOVE}">`);

container.querySelector('canvas').getContext('2d').drawImage(canvasKit.getCanvasBuffer(canvas), 0, 0);

上述代码之后，就可以在页面中看到一个棋盘网格。

2.4 示例二：绘制饼状图

下面以一个更为复杂的示例，来演示Canvaskit的使用。

const data = [
  { value: 10, label: 'Apple' },
  { value: 20, label: 'Banana' },
  { value: 30, label: 'Cherry' },
  { value: 40, label: 'Durian' }
];
const total = data.reduce((acc, cur) => acc + cur.value, 0);
const canvasWidth = 400;
const canvasHeight = 400;
const radius = Math.min(canvasWidth, canvasHeight) / 2 - 10;
const center = { x: canvasWidth / 2, y: canvasHeight / 2 };

const drawPieChart = (canvas, canvasKit) => {
    let startAngle = 0;
    let endAngle = 0;

    data.forEach((item) => {
        const paint = new canvasKit.Paint();
        paint.setStyle(canvasKit.PaintStyle.Fill);
        paint.setColor(canvasKit.makeColor(
            Math.round(Math.random() * 255),
            Math.round(Math.random() * 255),
            Math.round(Math.random() * 255),
            1
        ));

        startAngle = endAngle;
        endAngle = endAngle + item.value / total * 2 * Math.PI;

        const path = new canvasKit.Path();
        path.moveTo(center.x, center.y);
        path.lineTo(center.x + radius * Math.cos(startAngle), center.y + radius * Math.sin(startAngle));
        path.arcTo(canvasKit.makeRect(center.x - radius, center.y - radius, center.x + radius, center.y + radius), startAngle, endAngle - startAngle, false);
        path.close();

        canvas.drawPath(path, paint);
    });
};

const canvasKit = await CanvasKit.initCanvasKit();
const canvas = canvasKit.MakeCanvas(canvasWidth, canvasHeight);

drawPieChart(canvas, canvasKit);

const container = document.getElementById('container');
container.appendChild(html`<canvas width="${canvasWidth}" height="${canvasHeight}">`);

container.querySelector('canvas').getContext('2d').drawImage(canvasKit.getCanvasBuffer(canvas), 0, 0);

上述代码之后，就可以在页面中看到一个饼状图。