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Text reflow on zoom by pinch gesture (mobile)

This userscript tries to fit text to screen width after pinch gesture. It tries to replicate text reflow feature from Opera Mobile.

当前为 2024-10-30 提交的版本，查看 最新版本。

// ==UserScript==
// @name         Text reflow on zoom by pinch gesture (mobile)
// @description  This userscript tries to fit text to screen width after pinch gesture. It tries to replicate text reflow feature from Opera Mobile.
// @description:ru Этот скрипт пытается подогнать текст под ширину экрана после жеста увеличения на телефоне. Он воспроизводит функцию переноса текста из Opera Mobile.
// @version      1.0.0
// @author       emvaized
// @license      MIT
// @namespace    text_reflow_on_pinch_zoom
// @match        *://*/*
// @grant        none
// @run-at       document-start
// ==/UserScript==

(function() {
    'use strict';

    let isCssInjected = false, isPinching = false;
    let zoomTarget, targetDyOffsetRatio;
    const textElementsSelector = 'p, a, h1, h2, h3, h4, h5, h6, li, strong, em, span';

    // Function to adjust only outermost text-containing elements to the viewport width
    function processElement(element){
        element.classList.add('text-reflowed-userscript')
    }

    function reflowText() {
        if (!isCssInjected) {
            const styleContent = `.text-reflowed-userscript { word-wrap: break-word !important; overflow-wrap:break-word !important; max-width:var(--reflow-max-width) !important; }`;
            const styleElement = document.createElement("style");
            styleElement.textContent = styleContent;
            document.head.appendChild(styleElement);
        }

        const maxAllowedWidth = window.visualViewport.width * 0.96;
        document.documentElement.style.setProperty('--reflow-max-width', `${maxAllowedWidth}px`);

        // Select elements likely to contain text
        const textElements = document.querySelectorAll(textElementsSelector);
        textElements.forEach(element => processElement(element));

        /// Scroll initial target element into view
        if (zoomTarget && targetDyOffsetRatio) {
            setTimeout(t => {
                // Scroll element into view horizontally
                zoomTarget.scrollIntoView({ behavior: "instant", block: "nearest", inline: "center" });

                // Scroll to element vertically, according to new page layout
                const targetOffset = targetDyOffsetRatio * window.innerHeight;
                const rect = zoomTarget.getBoundingClientRect();
                const targetTop = rect.top + window.pageYOffset;
                const scrollToPosition = targetTop - targetOffset;
                
                window.scrollTo({
                    top: scrollToPosition,
                    behavior: "instant"
                });

                // Reset the target and offset after scrolling
                zoomTarget = null;
                targetDyOffsetRatio = null;
            }, 5);
        }
    }

    // Detect start of multi-touch (pinch) gesture
    function handleTouchStart(event) {
        if (!event.touches || event.touches.length >= 2) {
            isPinching = true;

            // Store info about possible target of zoom gesture
            if (event.target) zoomTarget = event.target;

            // Calculate the midpoint between the two touch points
            const touch1 = event.touches[0];
            const touch2 = event.touches[1];
            const midpointX = (touch1.clientX + touch2.clientX) / 2;
            const midpointY = (touch1.clientY + touch2.clientY) / 2;
            
            // Use document.elementFromPoint to get the element at the midpoint
            let possibleZoomTarget;
            const elementsFromPoint = document.elementsFromPoint(midpointX, midpointY);
            for (let i = 0, n = elementsFromPoint.length, element; i < n; i++) {
                element = elementsFromPoint[i];
                if (element.matches(textElementsSelector)) {
                    possibleZoomTarget = element;
                    break;
                }
            }
            if (!possibleZoomTarget) possibleZoomTarget = elementsFromPoint[0];
            
            if (!possibleZoomTarget) return;
            zoomTarget = possibleZoomTarget;
            const targetRect= zoomTarget.getBoundingClientRect(); 
            targetDyOffsetRatio = targetRect.top / window.innerHeight;
        }
    }

    // Detect end of multi-touch (pinch) gesture
    function handleTouchEnd(event) {
        if (isPinching && (!event.touches || event.touches.length === 0)) {
            isPinching = false;
            reflowText();
        }
    }

    // Add event listeners
    window.addEventListener('touchstart', handleTouchStart);
    window.addEventListener('touchend', handleTouchEnd);

    /// Uncomment for experimental trackpad support in Safari
    // window.addEventListener('gesturestart', handleTouchStart);
    // window.addEventListener('gestureend', handleTouchEnd);
})();