79 lines
4.1 KiB
JavaScript
79 lines
4.1 KiB
JavaScript
/**
|
|
* 用于计算图片的宽高比例
|
|
* @see https://drafts.csswg.org/css-images-3/#sizing-terms
|
|
*
|
|
* ## 名词解释
|
|
* ### intrinsic dimensions
|
|
* 图片本身的尺寸
|
|
*
|
|
* ### specified size
|
|
* 用户指定的元素尺寸
|
|
*
|
|
* ### concrete object size
|
|
* 应用了 `objectFit` 之后图片的显示尺寸
|
|
*
|
|
* ### default object size
|
|
*/
|
|
export function calculateConcreteRect(style, intrinsicSize, specifiedSize) {
|
|
var _a, _b;
|
|
const isContain = style.objectFit === 'contain';
|
|
const specifiedPosition = style.specifiedPosition || [0, 0];
|
|
// ratio 越大表示矩形越"扁"
|
|
let intrinsicRatio = intrinsicSize.width / intrinsicSize.height;
|
|
let specifiedRatio = specifiedSize.width / specifiedSize.height;
|
|
/** 图片原始尺寸与最终尺寸之比 */
|
|
let concreteScale = 1;
|
|
if (intrinsicRatio > specifiedRatio && style.objectFit == "contain" ||
|
|
intrinsicRatio <= specifiedRatio && style.objectFit == "cover")
|
|
// 图片较"胖"时完整显示图片，图片较"瘦"时完全覆盖容器
|
|
// 这两种情况下有 concreteRect.width = specifiedSize.width
|
|
// 因为 concreteRect.width = intrinsicSize.width * concreteScale
|
|
// 所以:
|
|
concreteScale = specifiedSize.width / intrinsicSize.width;
|
|
else if (intrinsicRatio > specifiedRatio && style.objectFit == "cover" ||
|
|
intrinsicRatio <= specifiedRatio && style.objectFit == "contain")
|
|
// 图片较"瘦"时完整显示图片，图片较"胖"时完全覆盖容器
|
|
// 这两种情况下有 concreteRect.height = specifiedSize.height
|
|
// 因为 concreteRect.height = intrinsicSize.height * concreteScale
|
|
// 所以:
|
|
concreteScale = specifiedSize.height / intrinsicSize.height;
|
|
else
|
|
throw new Error("Unkonwn concreteScale");
|
|
let concreteRectWidth = intrinsicSize.width * concreteScale;
|
|
let concreteRectHeight = intrinsicSize.height * concreteScale;
|
|
// 这里可以把 left top 的计算想象成投影
|
|
let xRelativeOrigin = { left: 0, center: .5, right: 1 }[((_a = style.intrinsicPosition) === null || _a === void 0 ? void 0 : _a[0]) || "center"];
|
|
let yRelativeOrigin = { top: 0, center: .5, bottom: 1 }[((_b = style.intrinsicPosition) === null || _b === void 0 ? void 0 : _b[1]) || "center"];
|
|
let concreteRectLeft = (specifiedSize.width - concreteRectWidth) * xRelativeOrigin;
|
|
let concreteRectTop = (specifiedSize.height - concreteRectHeight) * yRelativeOrigin;
|
|
if (isContain) {
|
|
concreteRectLeft += specifiedPosition[0];
|
|
concreteRectTop += specifiedPosition[1];
|
|
}
|
|
// 这里有两个坐标系，一个是 specified (dist) 的坐标系，一个是 intrinsic (src) 的坐标系
|
|
// 这里将两个坐标系的点位置进行变换
|
|
// 例: 带入 x=0, y=0, 得到的结果就是 specifiedRect 的左上角在 intrinsic 坐标系下的坐标位置
|
|
// 在 specified 坐标系下, intrinsic 的零点在 (concreteRectLeft, concreteRectTop), 缩放为 concreteScale
|
|
// 所以有 x_dist = x_src * concreteScale + concreteRectLeft
|
|
// y_dist = y_src * concreteScale + concreteRectTop
|
|
let dist2src = (distX, distY) => [
|
|
/* srcX = */ (distX - concreteRectLeft) / concreteScale,
|
|
/* srcY = */ (distY - concreteRectTop) / concreteScale
|
|
];
|
|
let [srcLeft, srcTop] = dist2src(0, 0);
|
|
// srcRight = 图片 specified 框右边在 src 坐标系下的 x 坐标
|
|
// srcBottom = 图片 specified 框下边在 src 坐标系下的 y 坐标
|
|
let [srcRight, srcBottom] = dist2src(specifiedSize.width, specifiedSize.height);
|
|
// 这里要对 src 和 disc 两个框进行约束
|
|
return {
|
|
sx: Math.max(srcLeft, 0),
|
|
sy: Math.max(srcTop, 0),
|
|
sw: Math.min(srcRight - srcLeft, intrinsicSize.width),
|
|
sh: Math.min(srcBottom - srcTop, intrinsicSize.height),
|
|
dx: isContain ? Math.max(concreteRectLeft, 0) : specifiedPosition[0],
|
|
dy: isContain ? Math.max(concreteRectTop, 0) : specifiedPosition[1],
|
|
dw: Math.min(concreteRectWidth, specifiedSize.width),
|
|
dh: Math.min(concreteRectHeight, specifiedSize.height)
|
|
};
|
|
}
|