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js 实现画板

2026-02-01 19:47:32JavaScript

使用 Canvas API 实现基础画板

HTML 中创建 <canvas> 元素并设置宽高：

<canvas id="drawing-board" width="800" height="600"></canvas>

JavaScript 获取画布上下文并初始化绘图参数：

const canvas = document.getElementById('drawing-board');
const ctx = canvas.getContext('2d');
let isDrawing = false;
let currentColor = '#000000';
let brushSize = 5;

鼠标事件绑定实现绘图功能

监听鼠标事件控制绘图状态：

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

function startDrawing(e) {
    isDrawing = true;
    draw(e); // 立即绘制起点
}

function draw(e) {
    if (!isDrawing) return;
    ctx.lineCap = 'round';
    ctx.lineJoin = 'round';
    ctx.strokeStyle = currentColor;
    ctx.lineWidth = brushSize;

    ctx.lineTo(e.offsetX, e.offsetY);
    ctx.stroke();
    ctx.beginPath();
    ctx.moveTo(e.offsetX, e.offsetY);
}

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

添加颜色和粗细控制功能

创建颜色选择器和画笔粗细滑块：

<input type="color" id="color-picker" value="#000000">
<input type="range" id="brush-size" min="1" max="50" value="5">

JavaScript 更新绘图参数：

document.getElementById('color-picker').addEventListener('change', (e) => {
    currentColor = e.target.value;
});

document.getElementById('brush-size').addEventListener('input', (e) => {
    brushSize = e.target.value;
});

实现清除画布功能

添加清除按钮和对应逻辑：

<button id="clear-btn">清除画布</button>

<script>
document.getElementById('clear-btn').addEventListener('click', () => {
    ctx.clearRect(0, 0, canvas.width, canvas.height);
});
</script>

保存绘图为图片

添加保存功能按钮：

<button id="save-btn">保存图片</button>

<script>
document.getElementById('save-btn').addEventListener('click', () => {
    const link = document.createElement('a');
    link.download = 'drawing.png';
    link.href = canvas.toDataURL('image/png');
    link.click();
});
</script>

响应式布局优化

CSS 确保画布适应不同屏幕：

canvas {
    border: 1px solid #000;
    display: block;
    margin: 0 auto;
    background-color: white;
}

.controls {
    display: flex;
    justify-content: center;
    gap: 20px;
    margin: 10px;
}

触摸屏设备支持

添加触摸事件处理：

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);
}

js 实现画板