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js实现画笔功能

2026-03-01 14:58:52JavaScript

实现基础画布与画笔功能

创建一个HTML文件并添加<canvas>元素作为画布。通过JavaScript获取画布上下文并设置初始样式：

<canvas id="drawCanvas" width="800" height="600"></canvas>
<script>
  const canvas = document.getElementById('drawCanvas');
  const ctx = canvas.getContext('2d');
  ctx.strokeStyle = '#000000';
  ctx.lineWidth = 5;
  ctx.lineCap = 'round';
</script>

监听鼠标事件实现绘制

绑定鼠标事件来跟踪绘制动作。需要处理mousedown、mousemove和mouseup事件：

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

canvas.addEventListener('mousedown', (e) => {
  isDrawing = true;
  [lastX, lastY] = [e.offsetX, e.offsetY];
});

canvas.addEventListener('mousemove', (e) => {
  if (!isDrawing) return;
  ctx.beginPath();
  ctx.moveTo(lastX, lastY);
  ctx.lineTo(e.offsetX, e.offsetY);
  ctx.stroke();
  [lastX, lastY] = [e.offsetX, e.offsetY];
});

canvas.addEventListener('mouseup', () => isDrawing = false);
canvas.addEventListener('mouseout', () => isDrawing = false);

添加触摸屏支持

为移动设备添加触摸事件处理：

canvas.addEventListener('touchstart', (e) => {
  e.preventDefault();
  isDrawing = true;
  const touch = e.touches[0];
  const rect = canvas.getBoundingClientRect();
  [lastX, lastY] = [touch.clientX - rect.left, touch.clientY - rect.top];
});

canvas.addEventListener('touchmove', (e) => {
  if (!isDrawing) return;
  e.preventDefault();
  const touch = e.touches[0];
  const rect = canvas.getBoundingClientRect();
  const x = touch.clientX - rect.left;
  const y = touch.clientY - rect.top;
  ctx.beginPath();
  ctx.moveTo(lastX, lastY);
  ctx.lineTo(x, y);
  ctx.stroke();
  [lastX, lastY] = [x, y];
});

canvas.addEventListener('touchend', () => isDrawing = false);

实现画笔属性调整

添加控制面板来调整画笔颜色和粗细：

<input type="color" id="colorPicker" value="#000000">
<input type="range" id="brushSize" min="1" max="50" value="5">

const colorPicker = document.getElementById('colorPicker');
const brushSize = document.getElementById('brushSize');

colorPicker.addEventListener('input', () => {
  ctx.strokeStyle = colorPicker.value;
});

brushSize.addEventListener('input', () => {
  ctx.lineWidth = brushSize.value;
});

添加清除画布功能

实现清除按钮来重置画布：

<button id="clearBtn">清除画布</button>

document.getElementById('clearBtn').addEventListener('click', () => {
  ctx.clearRect(0, 0, canvas.width, canvas.height);
});

优化绘制性能

使用requestAnimationFrame优化绘制性能：

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];
  requestAnimationFrame(() => draw(e));
}

canvas.addEventListener('mousedown', (e) => {
  isDrawing = true;
  [lastX, lastY] = [e.offsetX, e.offsetY];
  draw(e);
});

保存绘制内容

添加保存功能将画布内容导出为图片：

js实现画笔功能

<button id="saveBtn">保存图片</button>

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