如何缩放图像并将其居中放置为正方形尺寸？

Question

这些问题相似，但无济于事：this，this，this和this。

目标是在保留原始宽高比的同时将图像绘制到方形画布上，如果原始宽高比不是正方形，则将图像居中。

例如，拍摄所附的1262x2688图像。下面的代码将其尺寸调整为100x100，但会扭曲宽高比。

代码应：（1）缩放图像以适合100x100画布； （2）保持长宽比； （3）将图像在画布中垂直和水平居中放置。

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

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

    // Set canvas size.
    canvas[0].width = 100;
    canvas[0].height = 100;

    // Write image to canvas.
    context.drawImage(image, 0, 0, newWidth, newHeight);

图片

Answer 1

要在保留外观的同时将图像适合画布，请使用以下

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);

Answer 2

假设我正确地进行了计算，以下方法是否可行？

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
}

Answer 3

这是我们使用的代码：

    // 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);