forgejo/web_src/js/markup/mermaid.js
silverwind fd4e7447e7
Fix opaque background on mermaid diagrams (#21642) (#21652)
Backport #21642

Browsers introduce a opaque background on iframes if the iframe
element's color-scheme does not match the document's color scheme which
in case of a dark theme results in a mismatch and the browser adds a
white background. Avoid this by specifying the same color scheme outside
and inside the iframe.

See https://fvsch.com/transparent-iframes for more info.

My initial attempt was to make the iframe document the same color-scheme
as the parent page (light or dark) but with that, there was a ugly
background flash on load in Chrome because Chrome apparently always
loads iframe in light scheme initially. Firefox still shows a background
flash on load but this is not possible to get rid of and it's certainly
a browser bug.

Before:
<img width="1147" alt="Screen Shot 2022-10-31 at 13 30 55"
src="https://user-images.githubusercontent.com/115237/199017132-9828aace-bdd0-4ede-8118-359e72bcf2fe.png">

After:
<img width="1152" alt="Screen Shot 2022-10-31 at 13 30 36"
src="https://user-images.githubusercontent.com/115237/199017137-989a9e67-3fe0-445f-a191-df5bf290dabf.png">
2022-11-01 22:31:17 +00:00

68 lines
2.3 KiB
JavaScript

import {isDarkTheme} from '../utils.js';
const {mermaidMaxSourceCharacters} = window.config;
const iframeCss = `
:root {color-scheme: normal}
body {margin: 0; padding: 0}
#mermaid {display: block; margin: 0 auto}
`;
function displayError(el, err) {
el.closest('pre').classList.remove('is-loading');
const errorNode = document.createElement('div');
errorNode.setAttribute('class', 'ui message error markup-block-error mono');
errorNode.textContent = err.str || err.message || String(err);
el.closest('pre').before(errorNode);
}
export async function renderMermaid() {
const els = document.querySelectorAll('.markup code.language-mermaid');
if (!els.length) return;
const {default: mermaid} = await import(/* webpackChunkName: "mermaid" */'mermaid');
mermaid.initialize({
startOnLoad: false,
theme: isDarkTheme() ? 'dark' : 'neutral',
securityLevel: 'strict',
});
for (const el of els) {
const source = el.textContent;
if (mermaidMaxSourceCharacters >= 0 && source.length > mermaidMaxSourceCharacters) {
displayError(el, new Error(`Mermaid source of ${source.length} characters exceeds the maximum allowed length of ${mermaidMaxSourceCharacters}.`));
continue;
}
let valid;
try {
valid = mermaid.parse(source);
} catch (err) {
displayError(el, err);
}
if (!valid) {
el.closest('pre').classList.remove('is-loading');
continue;
}
try {
// can't use bindFunctions here because we can't cross the iframe boundary. This
// means js-based interactions won't work but they aren't intended to work either
mermaid.mermaidAPI.render('mermaid', source, (svgStr) => {
const heightStr = (svgStr.match(/viewBox="(.+?)"/) || ['', ''])[1].split(/\s+/)[3];
if (!heightStr) return displayError(el, new Error('Could not determine chart height'));
const iframe = document.createElement('iframe');
iframe.classList.add('markup-render');
iframe.sandbox = 'allow-scripts';
iframe.style.height = `${Math.ceil(parseFloat(heightStr))}px`;
iframe.srcdoc = `<html><head><style>${iframeCss}</style></head><body>${svgStr}</body></html>`;
el.closest('pre').replaceWith(iframe);
});
} catch (err) {
displayError(el, err);
}
}
}