如何将图像缩放并居中到正方形尺寸?

要使图像适合画布,同时保留纵横比,请使用以下命令

const w = image.naturalWidth;
const h = image.naturalHeight;

// Get the min scale to fit the image to the canvas
const scale = Math.min(canvas.width / w, canvas.height / h);

// Set the transform to scale the image, and center to the canvas
ctx.setTransform(scale, 0, 0, scale, canvas.width / 2, canvas.height / 2);

// draw the image offset by half its width and height to center and fit
ctx.drawImage(image, -w / 2, -h / 2, w, h);

// to reset the transform
// ctx.setTransform(1,0,0,1,0,0);

    // Create canvas element.
    var canvas = $(document.createElement("canvas"));

    // Get canvas context.
    var context = canvas[0].getContext("2d");

    // Set canvas size.
    canvas[0].width = canvasWidth;
    canvas[0].height = canvasHeight;

    // Set image size, must use image.naturalWidth and image.naturalHeight -- not image.width and image.height.
    const imageWidth = image.naturalWidth;
    const imageHeight = image.naturalHeight;

    // Set scale to fit image to canvas, 
    const scale = Math.min(canvasWidth/imageWidth, canvasHeight/imageHeight);

    // Set new image dimensions.
    const scaledWidth = imageWidth * scale;
    const scaledHeight = imageHeight * scale;

    // Draw image in center of canvas.
    context.drawImage(image, (canvasWidth - scaledWidth)/2, (canvasHeight - scaledHeight)/2, scaledWidth, scaledHeight);

假设我的计算是正确的,下面的方法可能有用吗?

ratio = image.width/image.height;
if (image.width > image.height) {
    output.height = ( 100 / ratio ) 
    output.width = 100
    output.x = 0
    output.y = (100 - output.height) / 2
} else {
    output.height = 100
    output.width = 100 * ratio
    output.x = (100 - output.width) / 2
    output.y = 0
}