Improve pixiv thumbnails

Stop pixiv from cropping thumbnails to a square. Use higher resolution thumbnails on Retina displays.
当前为 2020-01-26 提交的版本，查看最新版本。
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// ==UserScript==
// @name           Improve pixiv thumbnails
// @name:ja        pixivサムネイルを改善する
// @namespace      https://www.kepstin.ca/userscript/
// @license        MIT; https://spdx.org/licenses/MIT.html
// @version        20200126.0
// @description    Stop pixiv from cropping thumbnails to a square. Use higher resolution thumbnails on Retina displays.
// @description:ja 正方形にトリミングされて表示されるのを防止します。Retinaディスプレイで高解像度のサムネイルを使用します。
// @author         Calvin Walton
// @match          https://www.pixiv.net/*
// @match          https://dic.pixiv.net/*
// @match          https://en-dic.pixiv.net/*
// @exclude        https://www.pixiv.net/fanbox*
// @grant          none
// ==/UserScript==

// Copyright © 2020 Calvin Walton <[email protected]>
//
// Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files
// (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify,
// merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice (including the next paragraph) shall be included in all copies or
// substantial portions of the Software.
// 
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
// OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
// LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR
// IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

(function() {
    'use strict';

    // The src prefix: scheme and domain
    let src_prefix = 'https://i.pximg.net';
    // The src suffix for thumbnails
    let thumb_suffix = '_master1200.jpg';
    // A regular expression that matches pixiv thumbnail urls
    // Has 3 captures:
    // $1: thumbnail width (optional)
    // $2: thumbnail height (optional)
    // $3: everything in the URL after the thumbnail size up to the image suffix
    let src_regexp = /https?:\/\/i\.pximg\.net(?:\/c\/(\d+)x(\d+)(?:_[^\/]*)?)?\/(?:custom-thumb|img-master)\/(.*)_(?:custom|master|square)1200.jpg/;

    const image_sizes = [
        { size: 150, path: '/c/150x150' },
        { size: 240, path: '/c/240x240' },
        { size: 360, path: '/c/360x360_70' },
        { size: 600, path: '/c/600x600' },
        { size: 1200, path: '' }
    ];

    function genImageSet(size, url_stuff) {
        let set = [];
        for (const image_size of image_sizes) {
            set.push({
                src: `${src_prefix}${image_size.path}/img-master/${url_stuff}${thumb_suffix}`,
                scale: image_size.size / size
            });
        }
        let defaultSrc = null;
        for (const image of set) {
            if (image.scale >= window.devicePixelRatio) {
                defaultSrc = image.src;
                break;
            }
        }
        if (!defaultSrc) {
            defaultSrc = set[set.length - 1].src;
        }
        return { set, defaultSrc };
    }

    // Create a srcset= attribute on the img, with appropriate dpi scaling values
    // Also update the src= attribute to a value appropriate for current dpi
    function imgSrcset(img, size, url_stuff) {
        let imageSet = genImageSet(size, url_stuff);
        img.srcset = imageSet.set.map(image => `${image.src} ${image.scale}x`).join(', ');
        img.src = imageSet.defaultSrc;
        if (!img.attributes.width && !img.style.width) { img.style.width = `${size}px`; }
        if (!img.attributes.height && !img.style.height) { img.style.height = `${size}px`; }
    }

    // Set up a css background-image with image-set() where supported, falling back
    // to a single image
    function cssImageSet(node, size, url_stuff) {
        let imageSet = genImageSet(size, url_stuff);
        let cssImageList = imageSet.set.map(image => `url("${image.src}") ${image.scale}x`).join(', ');
        node.style.backgroundSize = 'contain';
        // The way the style properties work, if you try to assign an unsupported value, it does not
        // take effect, but a supported value replaces the old value. So assign in order of worst
        // to best
        // Fallback single image
        node.style.backgroundImage = `url("${imageSet.defaultSrc}")`;
        // webkit/blink prefixed image-set
        node.style.backgroundImage = `-webkit-image-set(${cssImageList})`;
        // CSS4 proposed standard image-set
        node.style.backgroundImage = `image-set(${cssImageList})`;
    }

    function findParentSize(node) {
        let size = 0;
        let e = node;
        while (!size) {
            if (e.attributes.width && e.attributes.height) {
                let width = +e.attributes.width.value;
                let height = +e.attributes.height.value;
                if (width && width > size) { size = width; }
                if (height && height > size) { size = height; }
                return size;
            }
            if (!e.parentElement) { return 0; }
            e = e.parentElement;
        }
    }

    // We're using some uncommon thumbnail dimensions, and pixiv might not have them pre-cached. The thumbnail
    // request sometimes errors out (404) on thumbnails that are slow to generate, so retry them until they
    // load
    function imgErrorHandler(event) {
        let self = this;
        if ((self.dataset.kepstinRetry|0) > 6) {
            console.log("gave up loading", self.src);
            return;
        }
        self.dataset.kepstinRetry = (self.dataset.kepstinRetry|0) + 1;
        let sleep = Math.min((self.dataset.kepstinRetry|0) * 2 + 1, 10);
        console.log("error loading", self.src, "try", self.dataset.kepstinRetry, "sleep", sleep);
        window.setTimeout(function() { console.log("reloading", self.src); self.src = self.src; }, sleep * 1000);
        event.stopImmediatePropagation();
        event.stopPropagation();
        return false;
    }

    function handleImg(node) {
        if (node.dataset.kepstinThumbnail) { return; }

        if (!node.src.startsWith(src_prefix)) { node.dataset.kepstinThumbnail = 'skip'; return; }

        let m = node.src.match(src_regexp);
        if (!m) { node.dataset.kepstinThumbnail = 'bad'; return; }

        let size = findParentSize(node);
        if (size < 16) { size = Math.max(node.clientWidth, node.clientHeight); }
        if (size < 16) { size = Math.max(m[1], m[2]); }
        if (size == 0) {
            console.log('calculated size is 0 for', node)
            return;
        }
        imgSrcset(node, size, m[3]);
        node.style.objectFit = 'contain';

        node.addEventListener('error', imgErrorHandler);
        node.dataset.kepstinThumbnail = 'ok';
    }

    function handleLayoutThumbnail(node) {
        if (node.dataset.kepstinThumbnail) { return; }
        // Check for lazy-loaded images, which have a temporary URL
        // They'll be updated later when the src is set
        if (node.src.startsWith('data:') || node.src.endsWith('transparent.gif')) { return; }
        if (!node.src.startsWith(src_prefix)) { node.dataset.kepstinThumbnail = 'skip'; return; }

        let m = node.src.match(src_regexp);
        if (!m) { node.dataset.kepstinThumbnail = 'bad'; return; }

        let width = m[1];
        let height = m[2];
        let size = Math.max(width, height);
        if (!size) { width = height = size = 1200 };

        node.width = node.style.width = width;
        node.height = node.style.height = height;

        imgSrcset(node, size, m[3]);
        node.style.objectFit = 'contain';

        node.addEventListener('error', imgErrorHandler);
        node.dataset.kepstinThumbnail = 'ok';
    }

    function handleDivBackground(node) {
        if (node.dataset.kepstinThumbnail) { return; }
        // Check for lazy-loaded images
        // They'll be updated later when the background image (in style attribute) is set
        if (node.classList.contains('js-lazyload') || node.classList.contains('lazyloaded') || node.classList.contains('lazyloading')) { return; }
        if (node.style.backgroundImage.indexOf(src_prefix) == -1) { node.dataset.kepstinThumbnail = 'skip'; return; }

        let m = node.style.backgroundImage.match(src_regexp);
        if (!m) { node.dataset.kepstinThumbnail = 'bad'; return; }

        let size = Math.max(node.clientWidth, node.clientHeight);
        if (size == 0) { size = Math.max(m[1], m[2]); }
        if (size == 0) {
            console.log('calculated size is 0 for', node)
            return;
        }
        if (node.firstElementChild) {
            // There's other stuff inside the DIV, don't do image replacement
            cssImageSet(node, size, m[3]);
            node.dataset.kepstinThumbnail = 'ok';
        }

        // Use IMG tags for images!
        let parentNode = node.parentElement;
        let img = document.createElement('IMG');
        imgSrcset(img, size, m[3]);
        img.class = node.class;
        img.alt = node.getAttribute('alt');
        img.style.width = node.style.width;
        img.style.height = node.style.height;
        img.style.objectFit = 'contain';

        img.addEventListener('error', imgErrorHandler);
        img.dataset.kepstinThumbnail = 'ok';

        node.replaceWith(img);
    }

    function handleABackground(node) {
        if (node.dataset.kepstinThumbnail) { return; }
        if (node.style.backgroundImage.indexOf(src_prefix) == -1) { node.dataset.kepstinThumbnail = 'skip'; return; }

        let m = node.style.backgroundImage.match(src_regexp);
        if (!m) { node.dataset.kepstinThumbnail = 'bad'; return; }

        let size = Math.max(node.clientWidth, node.clientHeight);
        if (size == 0) { size = Math.max(m[1], m[2]); }
        if (size == 0) {
            console.log('calculated size is 0 for', node)
            return;
        }

        if (node.firstElementChild) {
            // There's other stuff inside the A, don't do image replacement
            cssImageSet(node, size, m[3]);
            node.dataset.kepstinThumbnail = 'ok';
            return;
        }

        // Use IMG tags for images!
        let img = document.createElement('IMG');
        imgSrcset(img, size, m[3]);
        img.alt = '';
        img.style.width = '100%';
        img.style.height = '100%';
        img.style.objectFit = 'contain';
        img.style.position = 'absolute';

        img.addEventListener('error', imgErrorHandler);
        img.dataset.kepstinThumbnail = 'ok';

        node.style.backgroundImage = '';
        node.prepend(img);
    }

    function onetimeThumbnails(parentNode) {
        for (let node of parentNode.querySelectorAll('IMG')) {
            if (node.parentElement.classList.contains('_layout-thumbnail')) {
                handleLayoutThumbnail(node);
            } else {
                handleImg(node);
            }
        }
        for (let node of parentNode.querySelectorAll('DIV[style*=background-image]')) {
            handleDivBackground(node);
        }
        for (let node of parentNode.querySelectorAll('A[style*=background-image]')) {
            handleABackground(node);
        }
    }

    function mutationObserverCallback(mutationList, observer) {
        for (let mutation of mutationList) {
            switch (mutation.type) {
                case 'childList':
                    for (let node of mutation.addedNodes) {
                        if (node.nodeName == 'IMG') {
                            handleImg(node);
                        } else if (node.nodeName == 'DIV') {
                            if (node.style.backgroundImage) {
                                handleDivBackground(node);
                            } else {
                                onetimeThumbnails(node);
                            }
                        } else if (node.nodeName == 'A') {
                            if (node.style.backgroundImage) {
                                handleABackground(node);
                            }
                        } else if (node.nodeName == 'SECTION' || node.nodeName == 'LI' || node.nodeName == 'FIGURE') {
                            onetimeThumbnails(node);
                        }
                    }
                    break;
                case 'attributes':
                    if (mutation.target.nodeName == 'DIV') {
                        if (mutation.target.style.backgroundImage) {
                            handleDivBackground(mutation.target);
                        }
                    } else if (mutation.target.nodeName == 'IMG') {
                        if (mutation.target.parentElement.classList.contains('_layout-thumbnail')) {
                            handleLayoutThumbnail(mutation.target);
                        }
                    }
                    break;
            }
        }
    }

    if (!window.kepstinThumbnailObserver) {
        onetimeThumbnails(document.firstElementChild);
        window.kepstinThumbnailObserver = new MutationObserver(mutationObserverCallback);
        window.kepstinThumbnailObserver.observe(document.firstElementChild, {
            childList: true,
            subtree: true,
            attributes: true,
            attributeFilter: [ 'class', 'src' ]
        });
    }
})();