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js实现手写

2026-02-01 15:43:29JavaScript

实现手写功能的 JavaScript 方法

使用 Canvas API

通过 HTML5 的 <canvas> 元素结合 JavaScript 实现手写功能是一种常见方法。以下是一个基础实现示例：

const canvas = document.getElementById('drawingCanvas');
const ctx = canvas.getContext('2d');
let isDrawing = false;

canvas.addEventListener('mousedown', startDrawing);
canvas.addEventListener('mousemove', draw);
canvas.addEventListener('mouseup', stopDrawing);
canvas.addEventListener('mouseout', stopDrawing);

function startDrawing(e) {
    isDrawing = true;
    draw(e);
}

function draw(e) {
    if (!isDrawing) return;
    ctx.lineWidth = 5;
    ctx.lineCap = 'round';
    ctx.strokeStyle = '#000000';

    ctx.lineTo(e.clientX - canvas.offsetLeft, e.clientY - canvas.offsetTop);
    ctx.stroke();
    ctx.beginPath();
    ctx.moveTo(e.clientX - canvas.offsetLeft, e.clientY - canvas.offsetTop);
}

function stopDrawing() {
    isDrawing = false;
    ctx.beginPath();
}

触摸屏支持

对于移动设备，需要添加触摸事件支持：

canvas.addEventListener('touchstart', handleTouchStart);
canvas.addEventListener('touchmove', handleTouchMove);
canvas.addEventListener('touchend', handleTouchEnd);

function handleTouchStart(e) {
    e.preventDefault();
    const touch = e.touches[0];
    const mouseEvent = new MouseEvent('mousedown', {
        clientX: touch.clientX,
        clientY: touch.clientY
    });
    canvas.dispatchEvent(mouseEvent);
}

function handleTouchMove(e) {
    e.preventDefault();
    const touch = e.touches[0];
    const mouseEvent = new MouseEvent('mousemove', {
        clientX: touch.clientX,
        clientY: touch.clientY
    });
    canvas.dispatchEvent(mouseEvent);
}

function handleTouchEnd(e) {
    e.preventDefault();
    const mouseEvent = new MouseEvent('mouseup', {});
    canvas.dispatchEvent(mouseEvent);
}

压力敏感支持

对于支持压感的设备（如绘图板），可以使用 Pointer Events API：

canvas.addEventListener('pointerdown', startDrawing);
canvas.addEventListener('pointermove', draw);
canvas.addEventListener('pointerup', stopDrawing);
canvas.addEventListener('pointerout', stopDrawing);

function draw(e) {
    if (!isDrawing) return;
    ctx.lineWidth = e.pressure * 10;
    ctx.lineTo(e.clientX - canvas.offsetLeft, e.clientY - canvas.offsetTop);
    ctx.stroke();
    ctx.beginPath();
    ctx.moveTo(e.clientX - canvas.offsetLeft, e.clientY - canvas.offsetTop);
}

保存手写内容

可以将画布内容保存为图像：

function saveDrawing() {
    const dataURL = canvas.toDataURL('image/png');
    const link = document.createElement('a');
    link.download = 'drawing.png';
    link.href = dataURL;
    link.click();
}

清除画布

实现清除功能：

function clearCanvas() {
    ctx.clearRect(0, 0, canvas.width, canvas.height);
}

优化性能

对于复杂绘图，可以使用 requestAnimationFrame 优化性能：

function draw(e) {
    if (!isDrawing) return;
    requestAnimationFrame(() => {
        ctx.lineTo(e.clientX - canvas.offsetLeft, e.clientY - canvas.offsetTop);
        ctx.stroke();
        ctx.beginPath();
        ctx.moveTo(e.clientX - canvas.offsetLeft, e.clientY - canvas.offsetTop);
    });
}

这些方法组合起来可以创建一个完整的手写功能实现，支持桌面和移动设备，并具备基本的保存和清除功能。

js实现手写