JavaScript 放大镜 - 放大倍率和视窗尺寸

/**
 * 获取放大镜放大倍数
 * @param thumb		缩略图对象
 * @param glass		镜片对象
 * @return 			放大镜放大倍数
 */
function getMultiple(thumb, glass) {
	var multiple = {
		horizontal:0,
		vertical:0
	};
 
	var thumbSize = getSize(thumb);
	var imageSize = getImageSize(image);
 
	multiple.horizontal = imageSize.width / thumbSize.width;
	if(multiple.horizontal <= 1) {
		multiple.horizontal = 1;
	}
 
	multiple.vertical = imageSize.height / thumbSize.height;
	if(multiple.vertical <= 1) {
		multiple.vertical = 1;
	}
 
	return multiple;
}

/**
 * 加载镜片的样式
 * @param viewportSize	视窗尺寸
 * @param multiple		倍率
 * @param glass			镜片对象
 */
function loadGlassStyle(viewportSize, multiple, glass) {
	glass.style.width = round(viewportSize.width / multiple.horizontal) + 'px';
	glass.style.height = round(viewportSize.height / multiple.vertical) + 'px';
}

/**
 * 返回视窗尺寸
 * @param multiple		倍率
 * @param image			原图对象
 * @return				视窗尺寸
 */
getViewportSize: function(multiple, image) {
	var dimension = {
		width:0,
		height:0
	};
 
	// 如果倍率小于 1 或者视窗比原图还宽, 宽度设为跟原图一致, 否则去设定宽度
	if(multiple.horizontal <= 1 || config.viewportSize[0] > image.width) {
		dimension.width = image.width;
	} else {
		dimension.width = config.viewportSize[0];
	}
 
	// 如果倍率小于 1 或者视窗比原图还高, 高度设为跟原图一致, 否则去设定高度
	if(multiple.vertical <= 1 || config.viewportSize[1] > image.height) {
		dimension.height = image.height;
	} else {
		dimension.height = config.viewportSize[1];
	}
 
	return dimension;
}