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canvas 以鼠标为中心滑动滚轮缩放
let ctx = document.getElementById('canvas').getContext('2d');
let obj = {
fontX: 0,
fontY: 0,
fontZoom: 1,
curZoom: 1,
translateX: 0,
translateY: 0,
draw() {
ctx.fillRect(150, 150, 50, 50)
},
zoom(offsetX, offsetY, z) {
ctx.save()
ctx.clearRect(0, 0, 300, 300);
this.curZoom = this.fontZoom + z
this.translateX = offsetX - (offsetX - this.translateX) * this.curZoom / this.fontZoom
this.translateY = offsetY - (offsetY - this.translateY) * this.curZoom / this.fontZoom
ctx.translate(this.translateX, this.translateY)
ctx.scale(this.curZoom, this.curZoom);
this.draw()
ctx.restore()
this.fontY = offsetY
this.fontX = offsetX
this.fontZoom = this.curZoom
}
}
obj.draw()
document.getElementById('canvas').addEventListener('mousewheel', (e) => {
let z = e.deltaY > 0 ? -0.1 : 0.1
obj.zoom(e.offsetX, e.offsetY, z)
})
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