如何将图像缩放和居中到正方形尺寸？

Question

这些问题很相似，但没有帮助：this、this、this和this。目标是将图像绘制到方形画布上，同时保留原始纵横比，如果原始纵横比不是正方形，则将图像居中。例如，获取附加的 1262x2688 图像。下面的代码将其调整为 100x100，但它扭曲了纵横比。代码应该： (1) 缩放图像以适合 100x100 画布；(2) 保持纵横比；(3) 在画布内垂直和水平居中图像。    // 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

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);

Answer 2

要在保留外观的同时使图像适合画布，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);

Answer 3

假设我的计算方式正确，以下可能有效？

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

}