Use uniapp to implement image rotation function

Use uniapp to implement image rotation function

In mobile application development, we often encounter scenarios where images need to be rotated. For example, the angle needs to be adjusted after taking a photo. Or achieve an effect similar to the rotation of a camera after taking a picture. This article will introduce how to use the uniapp framework to implement the image rotation function and provide specific code examples.

uniapp is a cross-platform development framework based on Vue.js, which can simultaneously develop and publish applications for iOS, Android, H5 and other platforms. Implementing the image rotation function in uniapp mainly relies on two aspects: the canvas element in HTML5 and the basic API of uniapp.

First, we need to create a uni-app project and introduce a canvas element to the requirements page to display images. Add the following code to the HTML file:

<template>
  <view>
    <canvas canvas-id="myCanvas"></canvas>
  </view>
</template>

Next, in the script part of the page (.js file), we need to get the image to be rotated and draw the image into the canvas. The code is as follows:

<template>
  <view>
    <canvas canvas-id="myCanvas"></canvas>
  </view>
</template>

<script>
  export default {
    onReady() {
      this.drawRotateImage()
    },
    methods: {
      drawRotateImage() {
        const ctx = uni.createCanvasContext('myCanvas', this)
        uni.getImageInfo({
          src: 'path/to/image',
          success: (res) => {
            const imageWidth = res.width
            const imageHeight = res.height
  
            ctx.translate(imageWidth / 2, imageHeight / 2)
            ctx.rotate(Math.PI / 4)
            ctx.drawImage(res.path, -imageWidth / 2, -imageHeight / 2, imageWidth, imageHeight)
            ctx.draw()
          }
        })
      }
    }
  }
</script>

In the above code, we first create a canvas context (ctx) object and use the uni.getImageInfo() method to obtain the image information to be rotated. Then, use the ctx.translate() method to translate the origin of the canvas to the center of the picture, the ctx.rotate() method to rotate the canvas, and finally use the ctx.drawImage() method to draw the picture into the canvas.

The path/to/image in the code needs to be replaced with the actual image path. Regarding obtaining the image path, you can use the upload component of uni-app or the temporary file path returned after selecting the image through the uni.chooseImage() method.

After completing the writing of the above code, you can run the project in the uni-app development tool to view the image rotation effect. The angle of rotation can be changed by modifying the parameters of the ctx.rotate() method.

Summary:
This article introduces how to use the uniapp framework to implement the image rotation function, and provides specific code examples. By calling the canvas element in HTML5 and the uniapp API, we can implement image rotation requirements in mobile applications. Hope this article can be helpful to you.

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