javascript - 通过手机加载时， Canvas 图像将图像旋转 90 度

Question

我正在尝试制作一个小 Canvas 功能，它可以让您上传图片并在其上添加叠加层。我可以上传，在顶部创建图像并下载，但是当我尝试通过手机上传图像时。它将图像旋转 90 度。

我是不是漏掉了什么？在将图像添加到 Canvas 之前，我是否必须测试图像的大小并对其进行缩放？

任何帮助都会有很大的帮助，谢谢。

  <style>
    .box{
        width: 300px;
        height: 300px;
        border: 1px solid blue;
        padding: 1em;
    }
    .wrap{
        width: 180px;
        height: 180px;
        margin: 0 auto;
        background: red;
        position: relative;
    }
</style>
        <div class="box">
        <div class="wrap">
            <canvas id="canvas" width="180" height="180"></canvas>
        </div>
        <br />
        <label>Image File:</label><br/>
        <input type="file" id="imageLoader" name="imageLoader"/>
        <br />
        <br />
        <a href="#" clss="buttonLink" id="downloadLink">Download!</a>
    </div>
    <script>


        $(document).ready(function() {
            //upload images.
            var imageLoader = document.getElementById('imageLoader');
            imageLoader.addEventListener('change', handleImage, false);
            //draw image.
            var canvas = document.getElementById('canvas');
            var context = canvas.getContext('2d');
            //download link.
            var downloadLink = document.getElementById('downloadLink');

            //upload image.
            function handleImage(e){
                var reader = new FileReader();
                reader.onload = function(event){


            var img = new Image();
            img.setAttribute('crossOrigin', 'anonymous');

                    var width = 180;
                    var height = 180;
                    img.onload = function(){

                    context.drawImage(img,0,0, width, height);
                    var imageObj = new Image();
                        imageObj.setAttribute('crossOrigin', 'anonymous');
                    imageObj.onload = function() {
                      context.drawImage(imageObj, 69, 50);
                    };
                        imageObj.src = icon.png';
                    }
                    img.src = event.target.result;
                }
                reader.readAsDataURL(e.target.files[0]);     
            };              
            //download link.
            downloadLink.onclick = function () {
                downloadLink.href = canvas.toDataURL();
                downloadLink.download = 'facebook';
            };
        });
    </script> 

Answer 1

您需要读取 EXIF 数据并采取相应措施。读取数据的示例库: https://github.com/exif-js/exif-js

也已经回答了问题 JS Client-Side Exif Orientation: Rotate and Mirror JPEG Images

同样来自另一个来源，这是你应该如何处理 Canvas 上的 exif 方向:

switch(orientation){
    case 2:
        // horizontal flip
        ctx.translate(canvas.width, 0);
        ctx.scale(-1, 1);
        break;
    case 3:
        // 180° rotate left
        ctx.translate(canvas.width, canvas.height);
        ctx.rotate(Math.PI);
        break;
    case 4:
        // vertical flip
        ctx.translate(0, canvas.height);
        ctx.scale(1, -1);
        break;
    case 5:
        // vertical flip + 90 rotate right
        ctx.rotate(0.5 * Math.PI);
        ctx.scale(1, -1);
        break;
    case 6:
        // 90° rotate right
        ctx.rotate(0.5 * Math.PI);
        ctx.translate(0, -canvas.height);
        break;
    case 7:
        // horizontal flip + 90 rotate right
        ctx.rotate(0.5 * Math.PI);
        ctx.translate(canvas.width, -canvas.height);
        ctx.scale(-1, 1);
        break;
    case 8:
        // 90° rotate left
        ctx.rotate(-0.5 * Math.PI);
        ctx.translate(-canvas.width, 0);
        break;
}