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js实现手绘

2026-01-31 19:17:00JavaScript

使用Canvas实现手绘功能

在JavaScript中，可以通过HTML5的Canvas API实现手绘功能。Canvas提供了绘制路径的方法，适合用于创建绘图应用。

基本实现步骤

创建Canvas元素并设置基本样式

<canvas id="drawingCanvas" width="800" height="600"></canvas>

获取Canvas上下文并设置初始参数

const canvas = document.getElementById('drawingCanvas');
const ctx = canvas.getContext('2d');
ctx.strokeStyle = '#000000';
ctx.lineWidth = 5;
ctx.lineCap = 'round';

设置鼠标/触摸事件监听器

let isDrawing = false;
let lastX = 0;
let lastY = 0;

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

实现绘图函数

function startDrawing(e) {
    isDrawing = true;
    [lastX, lastY] = [e.offsetX, e.offsetY];
}

function draw(e) {
    if (!isDrawing) return;
    ctx.beginPath();
    ctx.moveTo(lastX, lastY);
    ctx.lineTo(e.offsetX, e.offsetY);
    ctx.stroke();
    [lastX, lastY] = [e.offsetX, e.offsetY];
}

function stopDrawing() {
    isDrawing = false;
}

添加触摸支持

为支持移动设备，需要添加触摸事件处理

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

function handleTouchStart(e) {
    e.preventDefault();
    const touch = e.touches[0];
    const rect = canvas.getBoundingClientRect();
    startDrawing({
        offsetX: touch.clientX - rect.left,
        offsetY: touch.clientY - rect.top
    });
}

function handleTouchMove(e) {
    e.preventDefault();
    const touch = e.touches[0];
    const rect = canvas.getBoundingClientRect();
    draw({
        offsetX: touch.clientX - rect.left,
        offsetY: touch.clientY - rect.top
    });
}

function handleTouchEnd() {
    stopDrawing();
}

增强功能实现

改变画笔颜色

function changeColor(color) {
    ctx.strokeStyle = color;
}

改变画笔粗细

function changeWidth(width) {
    ctx.lineWidth = width;
}

清除画布

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

保存绘图

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

使用压力敏感度（适用于支持压感的设备）

canvas.addEventListener('mousemove', (e) => {
    if (!isDrawing) return;
    const pressure = e.pressure || 0.5; // 默认值
    ctx.lineWidth = baseWidth * pressure;
    draw(e);
});

优化绘制性能

使用requestAnimationFrame优化绘制性能

js实现手绘

function draw(e) {
    if (!isDrawing) return;
    requestAnimationFrame(() => {
        ctx.beginPath();
        ctx.moveTo(lastX, lastY);
        ctx.lineTo(e.offsetX, e.offsetY);
        ctx.stroke();
        [lastX, lastY] = [e.offsetX, e.offsetY];
    });
}

实现橡皮擦功能

function enableEraser() {
    ctx.globalCompositeOperation = 'destination-out';
}

function disableEraser() {
    ctx.globalCompositeOperation = 'source-over';
}

这些代码片段提供了完整的绘图功能实现，可以根据需要进一步扩展和定制。