功能点：
- 鼠标拖拽canvas画布移动
- 鼠标检测rect
- 鼠标检测circle
代码
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<html lang="en"><head><meta charset="UTF-8" /><meta name="viewport" content="width=device-width, initial-scale=1.0" /><title>鼠标移动画布-事件检测</title><style>html,body {margin: 0;padding: 0;height: 100%;width: 100%;overflow: hidden;}</style></head><body><canvas id="canvas"></canvas><script>const canvas = document.getElementById('canvas');const { clientWidth: width, clientHeight: height } = document.body;canvas.width = width;canvas.height = height;const ctx = canvas.getContext('2d');// 储累积的偏移量let totalOffsetX = 0;let totalOffsetY = 0;// 缩放系数let scale = 1;// 图形数据const shapes = [{type: 'rect',x: 100,y: 100,width: 20,height: 20,strokeStyle: '#000',fillStyle: '#f00',},{type: 'circle',x: 200,y: 200,radius: 10,strokeStyle: '#000',fillStyle: '#0f0',},{type: 'polyline',points: [{ x: 200, y: 100 },{ x: 150, y: 100 },{ x: 200, y: 150 },],strokeStyle: '#000',fillStyle: '#00f',},];function render(offsetX, offsetY) {// 绘制时需要使用beginPath，否则无法使用clearRect清空画布ctx.clearRect(0, 0, width, height);ctx.fillStyle = '#999';ctx.fillRect(0, 0, width, height);ctx.fill();ctx.translate(totalOffsetX, totalOffsetY);ctx.scale(scale, scale);shapes.forEach((shape) => {const { type, x, y, width, height, radius, points } = shape;ctx.fillStyle = shape.fillStyle;ctx.beginPath();if (type === 'rect') {ctx.fillRect(x, y, width, height);} else if (type === 'circle') {ctx.arc(x, y, radius, 0, Math.PI * 2);} else if (type === 'polyline') {ctx.moveTo(points[0].x, points[0].y);points.slice(1).forEach((point) => {ctx.lineTo(point.x, point.y);});ctx.closePath();}ctx.fill();});ctx.resetTransform();}render();canvas.addEventListener('mousedown', onMouseDown);canvas.addEventListener('mousemove', onMouseMove);canvas.addEventListener('mouseup', onMouseUp);canvas.addEventListener('mouseleave', onMouseLeave);canvas.addEventListener('wheel', onWheel);let isMouseDown = false;let startX, startY;function onMouseDown(e) {canvas.style.cursor = 'grab';isMouseDown = true;startX = e.offsetX;startY = e.offsetY;}function onMouseMove(e) {isShapePoint(e);if (isMouseDown) {totalOffsetX += e.offsetX - startX;totalOffsetY += e.offsetY - startY;startX = e.offsetX;startY = e.offsetY;requestAnimationFrame(render);}}function onMouseUp(e) {isMouseDown = false;}function onMouseLeave(e) {isMouseDown = false;}function onWheel(e) {// 缩放，最大5倍，最小0.2倍if (e.deltaY === -100) {if (scale + 0.1 > 5) return;// 放大scale += 0.1;} else {if (scale - 0.1 <= 0.2) return;// 缩小scale -= 0.1;}requestAnimationFrame(render);}// 检测设备function isShapePoint(e) {const { offsetX, offsetY } = e;let check = false;shapes.forEach((shape) => {// 检测rectif (shape.type === 'rect') {const { type, x, y, width, height } = shape;const transformedX = (offsetX - totalOffsetX) / scale;const transformedY = (offsetY - totalOffsetY) / scale;if (transformedX >= x &&transformedX <= x + width &&transformedY >= y &&transformedY <= y + height) {check = true;}} else if (shape.type === 'circle') {// 检测圆形const { x, y, radius } = shape;const transformedX = (offsetX - totalOffsetX) / scale;const transformedY = (offsetY - totalOffsetY) / scale;const circleX = x;const circleY = y;// 计算光标与圆心的距离const distance = Math.sqrt((transformedX - circleX) ** 2 + (transformedY - circleY) ** 2);if (radius >= distance) {check = true;}} else if (shape.type === 'polyline') {const { points: polygon } = shape;let inside = false;const transformedX = (offsetX - totalOffsetX) / scale;const transformedY = (offsetY - totalOffsetY) / scale;for (let i = 0, j = polygon.length - 1;i < polygon.length;j = i++) {const xi = polygon[i].x,yi = polygon[i].y;const xj = polygon[j].x,yj = polygon[j].y;const intersect =yi > transformedY !== yj > transformedY &&transformedX <((xj - xi) * (transformedY - yi)) / (yj - yi) + xi;if (intersect) {inside = !inside;if (inside) {check = true;} else {check = false;}}}}});if (check) {canvas.style.cursor = 'move';} else {canvas.style.cursor = 'grab';}}</script></body>
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