canvas常用操作方法

base64转换Blob数据

function dataURLtoBlob(dataurl: string) {
    var arr = dataurl.split(','),
        mime = arr[0].match(/:(.*?);/)[1],
        bstr = atob(arr[1]),
        n = bstr.length,
        u8arr = new Uint8Array(n);
    while (n--) {
        u8arr[n] = bstr.charCodeAt(n);
    }
    eturn new Blob([u8arr], { type: mime });
}

// 使用示例：

var imgData = canvas.toDataURL({ format: 'png', quality: 1, width: 20000, height: 4000 });

var blob = dataURLtoBlob(imgData);

canvas.toBlob(function (blob) {
 console.log(blob)
 saveAs(blob, '图片下载.jpeg')
})

function getBase64Image(img) {
    var canvas = document.createElement("canvas");
    canvas.width = img.width;
    canvas.height = img.height;
    var ctx = canvas.getContext("2d");
    ctx.drawImage(img, 0, 0, img.width, img.height);
    var dataURL = canvas.toDataURL("image/png");
    return dataURL
    // return dataURL.replace("data:image/png;base64,", "");
}

var imageData = ctx.getImageData(0, 0, canvas.width, canvas.height)
for (var i = 0; i < imageData.data.length; i += 4) {
    // 当该像素是透明的，则设置成白色
    if (imageData.data[i + 3] == 0) {
        imageData.data[i] = 255
        imageData.data[i + 1] = 255
        imageData.data[i + 2] = 255
        imageData.data[i + 3] = 255
    }
}
ctx.putImageData(imageData, 0, 0)