jquery Android图片预览方向-优快云博客

本文链接：https://blog.youkuaiyun.com/chenghucsdn/article/details/65435019

本文介绍了一种使用JavaScript实现的图片文件预览方法，并详细解释了如何读取图片文件的元数据，调整图片大小并旋转以适应不同的显示需求。

    selectFileImage : function(fileObj) {
        var file = fileObj.files[0];
        var Orientation = null;
        if (file) {
            // 位置情報
            EXIF.getData(file, function() {
                EXIF.getAllTags(this);
                Orientation = EXIF.getTag(this, 'Orientation');
            });

var fileReader = new FileReader();
fileReader.onload = function(e) {

                var image = new Image();
                image.src = e.target.result;
                image.onload = function() {
                    var expectWidth = this.naturalWidth;
                    var expectHeight = this.naturalHeight;

                    if (this.naturalWidth > this.naturalHeight && this.naturalWidth > 800) {
                        expectWidth = 800;
                        expectHeight = expectWidth * this.naturalHeight / this.naturalWidth;
                    } else if (this.naturalHeight > this.naturalWidth && this.naturalHeight > 1200) {
                        expectHeight = 1200;
                        expectWidth = expectHeight * this.naturalWidth / this.naturalHeight;
                    }

                    var canvas = document.createElement("canvas");
                    var ctx = canvas.getContext("2d");
                    canvas.width = expectWidth;
                    canvas.height = expectHeight;
                    ctx.drawImage(this, 0, 0, expectWidth, expectHeight);

                    var base64 = null;
                    var mpImg = new MegaPixImage(image);
                    mpImg.render(canvas, {
                        maxWidth: 800,
                        maxHeight: 1200,
                        quality: 0.8,
                        orientation: Orientation
                    });

base64 = canvas.toDataURL("image/jpeg", 0.8);

                    $("#img").attr("src", base64);
                };
            };
            fileReader.readAsDataURL(file);
        }
    }