What's the math behind CSS's background-size:cover

Question

I\'m creating an \"image generator\" where users can upload an image and add text and/or draw on it. The outputted image is a fixed size (698x450).

On the client side,

Answer 1

Thanks to mdi for pointing me in the right direction, but that didn't seem quite right. This is the solution that worked for me:

    $imgRatio = $imageHeight / $imageWidth;
    $canvasRatio = $canvasHeight / $canvasWidth;

    if ($canvasRatio > $imgRatio) {
        $finalHeight = $canvasHeight;
        $scale = $finalHeight / $imageHeight;
        $finalWidth = round($imageWidth * $scale , 0);
    } else {
        $finalWidth = $canvasWidth;
        $scale = $finalWidth / $imageWidth;
        $finalHeight = round($imageHeight * $scale , 0);
    }