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fix: eliminate rendering pane flash on keypress #1362

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fix: eliminate rendering pane flash on keypress #1362

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94 changes: 58 additions & 36 deletions MacDown/Code/Document/MPDocument.m
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Original file line number Diff line number Diff line change
Expand Up @@ -1069,49 +1069,71 @@ - (void)renderer:(MPRenderer *)renderer didProduceHTMLOutput:(NSString *)html

self.manualRender = self.preferences.markdownManualRender;

#if 0
// Unfortunately this DOM-replacing causes a lot of problems...
// 1. MathJax needs to be triggered.
// 2. Prism rendering is lost.
// 3. Potentially more.
// Essentially all JavaScript needs to be run again after we replace
// the DOM. I have no idea how many more problems there are, so we'll have
// to back off from the path for now... :(

// If we're working on the same document, try not to reload.
// If we're updating the same document, replace the body content via
// JavaScript instead of doing a full page reload. This avoids the visible
// flash/flicker that loadHTMLString: causes.
// After replacing the DOM, re-trigger syntax highlighting (Prism) and
// math rendering (MathJax) so those features continue to work.
if (self.isPreviewReady && [self.currentBaseUrl isEqualTo:baseUrl])
{
// HACK: Ideally we should only inject the parts that changed, and only
// get the parts we need. For now we only get a complete HTML codument,
// and rely on regex to get the parts we want in the DOM.

// Use the existing tree if available, and replace the content.
DOMDocument *doc = self.preview.mainFrame.DOMDocument;
DOMNodeList *htmlNodes = [doc getElementsByTagName:@"html"];
if (htmlNodes.length >= 1)
// Extract <body> content from the rendered HTML.
static NSString *bodyPattern = @"<body[^>]*>(.*)</body>";
static int opts = NSRegularExpressionDotMatchesLineSeparators
| NSRegularExpressionCaseInsensitive;

NSRegularExpression *regex =
[[NSRegularExpression alloc] initWithPattern:bodyPattern
options:opts error:NULL];
NSTextCheckingResult *result =
[regex firstMatchInString:html options:0
range:NSMakeRange(0, html.length)];

if (result && result.numberOfRanges >= 2)
{
static NSString *pattern = @"<html>(.*)</html>";
static int opts = NSRegularExpressionDotMatchesLineSeparators;

// Find things inside the <html> tag.
NSRegularExpression *regex =
[[NSRegularExpression alloc] initWithPattern:pattern
options:opts error:NULL];
NSTextCheckingResult *result =
[regex firstMatchInString:html options:0
range:NSMakeRange(0, html.length)];
html = [html substringWithRange:[result rangeAtIndex:1]];

// Replace everything in the old <html> tag.
DOMElement *htmlNode = (DOMElement *)[htmlNodes item:0];
htmlNode.innerHTML = html;

NSString *bodyContent = [html substringWithRange:
[result rangeAtIndex:1]];

// Escape for JS string literal: backslashes, backticks,
// dollar signs (template literal delimiters), and newlines.
bodyContent = [bodyContent stringByReplacingOccurrencesOfString:@"\\"
withString:@"\\\\"];
bodyContent = [bodyContent stringByReplacingOccurrencesOfString:@"`"
withString:@"\\`"];
bodyContent = [bodyContent stringByReplacingOccurrencesOfString:@"$"
withString:@"\\$"];

// Replace body innerHTML and re-trigger JS libraries.
NSString *js = [NSString stringWithFormat:
@"(function() {"
" document.body.innerHTML = `%@`;"
" if (typeof Prism !== 'undefined') Prism.highlightAll();"
" if (typeof MathJax !== 'undefined') {"
" if (MathJax.Hub) MathJax.Hub.Queue(['Typeset', MathJax.Hub]);"
" else if (MathJax.typeset) MathJax.typeset();"
" }"
" if (typeof hljs !== 'undefined') {"
" document.querySelectorAll('pre code').forEach(function(b) { hljs.highlightElement(b); });"
" }"
"})();",
bodyContent];

[self.preview stringByEvaluatingJavaScriptFromString:js];

// Signal rendering complete without going through the full
// frame load delegate cycle.
self.alreadyRenderingInWeb = NO;
if (self.preferences.editorShowWordCount)
[self updateWordCount];
if (self.preferences.editorSyncScrolling)
[self syncScrollers];
if (self.renderToWebPending)
[self.renderer parseAndRenderNow];
self.renderToWebPending = NO;
return;
}
}
#endif

// Reload the page if there's not valid tree to work with.
// Full page reload for initial load or when base URL changes.
[self.preview.mainFrame loadHTMLString:html baseURL:baseUrl];
self.currentBaseUrl = baseUrl;
}
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