JavaScript : 旋转图片并保存

图片旋转是通过 canvas rotate 方法进行旋转，然后保存

js代码:

<template>
  <div style="background: #ffffff;" id="root" >

    <div style="width: 700px;margin: auto;">
      <div><input type="file" accept="image/*" @change="open" /></div>
    <div><button @click="rotate(-1)">逆时针旋转90度</button> <button @click="rotate(1)">顺时针旋转90度</button>
      <button @click="reset">重置</button></div>
    <div id="wrapper" :style="{marginTop:'10px',background:'lightgray',position: 'relative',lineHeight:lineLength+'px',width:'700px',height:lineLength+'px',overflow: 'hidden'}" >
      <img id="img" :src="imgSrc"
           style="position: absolute; transform: rotateZ(0deg);" />
    </div>
      <div><button style="margin-top: 10px;" id="saveBtn" @click="save">保存</button></div>
    </div>

  </div>
</template>

<script>
//computed, ,watch
import {ref} from "vue";

export default {
  name: "RotateImg",
  setup() {
    //旋转的度数
    let roDeg = 0;

    //旋转
    const rotate = (deg) => {
      if (deg == -1) {
         roDeg = roDeg - 90;
      }
      if (deg == 1) {
        roDeg = roDeg + 90;
      }
      let box = document.getElementById('img');
      box.style.transform = 'rotateZ('+roDeg+'deg)';
      box.style.transitionDuration = '500ms';
      box.style.transitionTimingFunction = 'linear';
    }

    //重置
    const reset = () => {
      roDeg = 0;
      let box = document.getElementById('img');
      box.style.transform = 'rotateZ('+roDeg+'deg)';
      box.style.transitionDuration = '0ms';
      box.style.transitionTimingFunction = 'linear';
    };

    //图片的src
    const imgSrc = ref("");
    //图片的原宽高
    const imgWidth = ref(0);
    const imgHeight = ref(0);
    //读取图片的信息
    const open = (e) => {
      let file = e.target.files[0];
      let reader = new FileReader();
      reader.readAsDataURL(file);

      reader.onload = () =>{
        //清除原来记录的度数,清除原来的样式
        reset();
        //显示图片
        imgSrc.value = reader.result;
        //得到宽高
        let img = new Image();
        img.src= reader.result;
        img.onload = () => {
          //保存原始宽高
          imgWidth.value = img.width;
          imgHeight.value = img.height;
          //处理图片的显示宽度/高度
          let imgStyle = document.getElementById('img').getAttributeNode('style');
          let wrapper = document.getElementById('wrapper');
          if (img.width >= img.height) {
            let iHeight = (500*img.height) / img.width;
            let itop = (500-iHeight)/2;
            imgStyle.value = 'width:500px;left:100px;top:'+itop+'px;position:absolute;display: block;';
            wrapper.style.height = "500px";
          } else {
            let iWidth = (500*img.width) / img.height;
            let iLeft = (700 - iWidth) / 2;
            imgStyle.value = 'height:500px;top:50px;left:'+iLeft+'px;position:absolute;display: block;';
            wrapper.style.height = "600px";
          }
        }
      }
    }
    //保存图片
    const save = () => {
      let img = document.getElementById('img')
      //创建canvas
      const canvas = document.createElement('canvas')
      if (canvas.getContext) {
        let context = canvas.getContext('2d');
        let degree = getDegree(roDeg);
        //旋转context并画图
        if (degree === 0) {
          canvas.width = imgWidth.value;
          canvas.height = imgHeight.value;
          context.rotate(0 * Math.PI / 180);
          context.drawImage(img, 0, 0);
        } else if (degree === 90) {
          canvas.width = imgHeight.value;
          canvas.height = imgWidth.value;
          context.rotate(90 * Math.PI / 180);
          context.drawImage(img, 0, -imgHeight.value);
        } else if (degree === 180) {
          canvas.width = imgWidth.value;
          canvas.height = imgHeight.value;
          context.rotate(180 * Math.PI / 180);
          context.drawImage(img, -imgWidth.value, -imgHeight.value);
        } else if (degree === 270) {
          canvas.width = imgHeight.value;
          canvas.height = imgWidth.value;
          context.rotate(270 * Math.PI / 180);
          context.drawImage(img, -imgWidth.value, 0);
        }
        downJpgByCanvas(canvas);
      }
    }

    //得到计算后的旋转度数
    const getDegree = (deg) => {
      let abs = Math.abs(deg);
      console.log('abs:'+abs);
      let yvshu = abs % 360;
      console.log('yvshu:'+yvshu);
      if (deg >= 0) {
        return yvshu;
      } else {
        if (yvshu == 0) {
            return 0;
        } else {
            return 360+(0-yvshu);
        }
      }
    }

    //下载图片
    const downJpgByCanvas = (canvas) => {
      var oA = document.createElement("a");
      let time = timeFormat();
      oA.download = "img_"+time+'.jpg';// 设置下载的文件名，默认是'下载'
      oA.href = canvas.toDataURL("image/jpeg");
      document.body.appendChild(oA);
      oA.click();
      oA.remove(); // 下载之后把创建的元素删除
    }

    //补0
    const add0 = (m) => {
      return m<10?'0'+m:m
    }
    //格式化时间
    const timeFormat = ()=>{
      var time = new Date();
      var y = time.getFullYear();
      var m = time.getMonth()+1;
      var d = time.getDate();
      var h = time.getHours();
      var mm = time.getMinutes();
      var s = time.getSeconds();
      let res = y+add0(m)+add0(d)+add0(h)+add0(mm)+add0(s);
      return res;
    }

    return {
      rotate,
      reset,
      open,
      save,
      imgSrc,
    }
  }
}
</script>

<style scoped>

</style>