geometry.js

import defineConfigurable from './defineConfigurable.js';
import getWindowOf from './getWindowOf.js';
import isBrowser from './isBrowser.js';

// Placeholder of an empty content rectangle.
const emptyRect = createRectInit(0, 0, 0, 0);

/**
 * Converts provided string to a number.
 *
 * @param {number|string} value
 * @returns {number}
 */
function toFloat(value) {
    return parseFloat(value) || 0;
}

/**
 * Extracts borders size from provided styles.
 *
 * @param {CSSStyleDeclaration} styles
 * @param {...string} positions - Borders positions (top, right, ...)
 * @returns {number}
 */
function getBordersSize(styles, ...positions) {
    return positions.reduce((size, position) => {
        const value = styles['border-' + position + '-width'];

        return size + toFloat(value);
    }, 0);
}

/**
 * Extracts paddings sizes from provided styles.
 *
 * @param {CSSStyleDeclaration} styles
 * @returns {Object} Paddings box.
 */
function getPaddings(styles) {
    const positions = ['top', 'right', 'bottom', 'left'];
    const paddings = {};

    for (const position of positions) {
        const value = styles['padding-' + position];

        paddings[position] = toFloat(value);
    }

    return paddings;
}

/**
 * Calculates content rectangle of provided SVG element.
 *
 * @param {SVGGraphicsElement} target - Element content rectangle of which needs
 *      to be calculated.
 * @returns {DOMRectInit}
 */
function getSVGContentRect(target) {
    const bbox = target.getBBox();

    return createRectInit(0, 0, bbox.width, bbox.height);
}

/**
 * Calculates content rectangle of provided HTMLElement.
 *
 * @param {HTMLElement} target - Element for which to calculate the content rectangle.
 * @returns {DOMRectInit}
 */
function getHTMLElementContentRect(target) {
    // Client width & height properties can't be
    // used exclusively as they provide rounded values.
    const {clientWidth, clientHeight} = target;

    // By this condition we can catch all non-replaced inline, hidden and
    // detached elements. Though elements with width & height properties less
    // than 0.5 will be discarded as well.
    //
    // Without it we would need to implement separate methods for each of
    // those cases and it's not possible to perform a precise and performance
    // effective test for hidden elements. E.g. even jQuery's ':visible' filter
    // gives wrong results for elements with width & height less than 0.5.
    if (!clientWidth && !clientHeight) {
        return emptyRect;
    }

    const styles = getWindowOf(target).getComputedStyle(target);
    const paddings = getPaddings(styles);
    const horizPad = paddings.left + paddings.right;
    const vertPad = paddings.top + paddings.bottom;

    // Computed styles of width & height are being used because they are the
    // only dimensions available to JS that contain non-rounded values. It could
    // be possible to utilize the getBoundingClientRect if only it's data wasn't
    // affected by CSS transformations let alone paddings, borders and scroll bars.
    let width = toFloat(styles.width),
        height = toFloat(styles.height);

    // Width & height include paddings and borders when the 'border-box' box
    // model is applied (except for IE).
    if (styles.boxSizing === 'border-box') {
        // Following conditions are required to handle Internet Explorer which
        // doesn't include paddings and borders to computed CSS dimensions.
        //
        // We can say that if CSS dimensions + paddings are equal to the "client"
        // properties then it's either IE, and thus we don't need to subtract
        // anything, or an element merely doesn't have paddings/borders styles.
        if (Math.round(width + horizPad) !== clientWidth) {
            width -= getBordersSize(styles, 'left', 'right') + horizPad;
        }

        if (Math.round(height + vertPad) !== clientHeight) {
            height -= getBordersSize(styles, 'top', 'bottom') + vertPad;
        }
    }

    // Following steps can't be applied to the document's root element as its
    // client[Width/Height] properties represent viewport area of the window.
    // Besides, it's as well not necessary as the <html> itself neither has
    // rendered scroll bars nor it can be clipped.
    if (!isDocumentElement(target)) {
        // In some browsers (only in Firefox, actually) CSS width & height
        // include scroll bars size which can be removed at this step as scroll
        // bars are the only difference between rounded dimensions + paddings
        // and "client" properties, though that is not always true in Chrome.
        const vertScrollbar = Math.round(width + horizPad) - clientWidth;
        const horizScrollbar = Math.round(height + vertPad) - clientHeight;

        // Chrome has a rather weird rounding of "client" properties.
        // E.g. for an element with content width of 314.2px it sometimes gives
        // the client width of 315px and for the width of 314.7px it may give
        // 314px. And it doesn't happen all the time. So just ignore this delta
        // as a non-relevant.
        if (Math.abs(vertScrollbar) !== 1) {
            width -= vertScrollbar;
        }

        if (Math.abs(horizScrollbar) !== 1) {
            height -= horizScrollbar;
        }
    }

    return createRectInit(paddings.left, paddings.top, width, height);
}

/**
 * Checks whether provided element is an instance of the SVGGraphicsElement.
 *
 * @param {Element} target - Element to be checked.
 * @returns {boolean}
 */
const isSVGGraphicsElement = (() => {
    // Some browsers, namely IE and Edge, don't have the SVGGraphicsElement
    // interface.
    if (typeof SVGGraphicsElement !== 'undefined') {
        return target => target instanceof getWindowOf(target).SVGGraphicsElement;
    }

    // If it's so, then check that element is at least an instance of the
    // SVGElement and that it has the "getBBox" method.
    // eslint-disable-next-line no-extra-parens
    return target => (
        target instanceof getWindowOf(target).SVGElement &&
        typeof target.getBBox === 'function'
    );
})();

/**
 * Checks whether provided element is a document element (<html>).
 *
 * @param {Element} target - Element to be checked.
 * @returns {boolean}
 */
function isDocumentElement(target) {
    return target === getWindowOf(target).document.documentElement;
}

/**
 * Calculates an appropriate content rectangle for provided html or svg element.
 *
 * @param {Element} target - Element content rectangle of which needs to be calculated.
 * @returns {DOMRectInit}
 */
export function getContentRect(target) {
    if (!isBrowser) {
        return emptyRect;
    }

    if (isSVGGraphicsElement(target)) {
        return getSVGContentRect(target);
    }

    return getHTMLElementContentRect(target);
}

/**
 * Creates rectangle with an interface of the DOMRectReadOnly.
 * Spec: https://drafts.fxtf.org/geometry/#domrectreadonly
 *
 * @param {DOMRectInit} rectInit - Object with rectangle's x/y coordinates and dimensions.
 * @returns {DOMRectReadOnly}
 */
export function createReadOnlyRect({x, y, width, height}) {
    // If DOMRectReadOnly is available use it as a prototype for the rectangle.
    const Constr = typeof DOMRectReadOnly !== 'undefined' ? DOMRectReadOnly : Object;
    const rect = Object.create(Constr.prototype);

    // Rectangle's properties are not writable and non-enumerable.
    defineConfigurable(rect, {
        x, y, width, height,
        top: y,
        right: x + width,
        bottom: height + y,
        left: x
    });

    return rect;
}

/**
 * Creates DOMRectInit object based on the provided dimensions and the x/y coordinates.
 * Spec: https://drafts.fxtf.org/geometry/#dictdef-domrectinit
 *
 * @param {number} x - X coordinate.
 * @param {number} y - Y coordinate.
 * @param {number} width - Rectangle's width.
 * @param {number} height - Rectangle's height.
 * @returns {DOMRectInit}
 */
export function createRectInit(x, y, width, height) {
    return {x, y, width, height};
}