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fix(pdf-server): render page before O(numPages) annotation scans (#581)

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PR #506 added loadBaselineAnnotations() and buildFieldNameMap() between
showViewer() and renderPage(). Both iterate every page calling
getPage()+getAnnotations(), so the viewer sat with an unsized empty
canvas for ~400ms (15-page doc, scales linearly) before painting.

Neither scan blocks the canvas — page.render() only needs canvasContext
+ viewport. renderAnnotationsForPage() reads annotationMap (graceful
empty), AnnotationLayer.render() takes cachedFieldObjects (graceful
null). So: render first, scan after, re-render to overlay annotations
+ form values. Same fix at the reload path.
This commit is contained in:
Olivier Chafik 2026-04-01 22:45:45 +01:00 • committed by GitHub
commit 9d55050a00
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1 changed files with 22 additions and 10 deletions
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32
examples/pdf-server/src/mcp-app.ts
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@ -3896,11 +3896,16 @@ async function reloadPdf(): Promise<void> {
log.info("PDF reloaded:", totalPages, "pages,", totalBytes, "bytes");
showViewer();
// Render immediately — annotation/form scans below are O(numPages) and
// do NOT block the canvas. See same pattern in the initial-load path.
await renderPage();
await loadBaselineAnnotations(document);
await buildFieldNameMap(document);
syncFormValuesToStorage();
updateAnnotationsBadge();
renderAnnotationPanel();
renderPage();
startPreloading();
} catch (err) {
@ -4103,9 +4108,18 @@ app.ontoolresult = async (result: CallToolResult) => {
downloadBtn.style.display = app.getHostCapabilities()?.downloadFile
? ""
: "none";
// Save button visibility driven by setDirty()/updateSaveBtn();
// restoreAnnotations() above may have already shown it via setDirty(true).
updateSaveBtn();
// Compute fit + render IMMEDIATELY for fast first paint. The canvas is
// unsized until renderPage() runs — anything async between showViewer()
// and here makes the empty viewer visible. The annotation/form scans
// below are O(numPages) and do NOT block the canvas (page.render only
// needs canvasContext+viewport), so they run after.
const fitScale = await computeFitToWidthScale();
if (fitScale !== null) {
scale = fitScale;
log.info("Fit-to-width scale:", scale);
}
await renderPage();
// Import annotations from the PDF to establish baseline
await loadBaselineAnnotations(document);
@ -4118,14 +4132,12 @@ app.ontoolresult = async (result: CallToolResult) => {
syncFormValuesToStorage();
updateAnnotationsBadge();
// Save button visibility driven by setDirty()/updateSaveBtn();
// restoreAnnotations() may have just flipped it via setDirty(true).
updateSaveBtn();
// Compute fit-to-width scale for narrow containers (e.g. mobile)
const fitScale = await computeFitToWidthScale();
if (fitScale !== null) {
scale = fitScale;
log.info("Fit-to-width scale:", scale);
}
// Re-render to overlay PDF-baseline annotations + restored form values.
// For PDFs with neither, the canvas is identical → no flicker.
renderPage();
// Start background preloading of all pages for text extraction
startPreloading();