小程序 canvas放大缩小
时间: 2024-09-14 18:02:26 浏览: 76
在微信小程序的canvas组件中,如果需要实现放大或缩小功能,你可以通过改变其宽高属性来调整画布大小。但是要注意的是,Canvas本身并不支持直接的缩放,你需要手动计算每个坐标点的新位置,然后重新绘制。
以下是基本的步骤:
1. **获取原尺寸**:首先,在页面加载时,保存原始的canvas宽度和高度。
```javascript
Page({
onLoad: function() {
this.canvasWidth = wx.createSelectorQuery().select('#your-canvas-id').fields({size: true}).exec()[0].width;
this.canvasHeight = wx.createSelectorQuery().select('#your-canvas-id').fields({size: true}).exec()[0].height;
},
```
2. **响应事件处理**:当用户触发放大或缩小操作时,动态更新canvas的大小,并相应地改变所有绘制元素的位置。
```javascript
onZoom: function(scale) {
const newWidth = this.canvasWidth * scale;
const newHeight = this.canvasHeight * scale;
// 更新canvas的样式
document.getElementById('your-canvas-id').style.width = `${newWidth}px`;
document.getElementById('your-canvas-id').style.height = `${newHeight}px`;
// 如果有已绘制的图形,遍历并重新定位它们
let ctx = wx.createSelectorQuery().select('#your-canvas-id').context();
ctx.clearRect(0, 0, newWidth, newHeight);
for (let i = 0; i < yourDrawingObjects.length; i++) {
const oldX = yourDrawingObjects[i].x / scale;
const oldY = yourDrawingObjects[i].y / scale;
// 绘制新的位置
ctx.drawImage(...);
}
},
```
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