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Optimise rendering of Pageviewer pages for HiDPI screens #608

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Optimise rendering of Pageviewer pages for HiDPI screens #608

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13 changes: 11 additions & 2 deletions frontend/src/js/components/PageViewer/PdfHelpers.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -84,8 +84,17 @@ const renderPagePreview = async (

const viewport = pdfPage.getViewport({ scale });

canvas.width = viewport.width;
canvas.height = viewport.height;
// Render at higher resolution on HiDPI displays for sharper text.
// The canvas backing store is multiplied by DPR, but CSS dimensions
// are set to the logical size so the layout footprint is unchanged.
// Critically, `scale` (returned in CachedPreview) stays as the logical
// scale — text overlays and highlight geometry depend on this.
const dpr = window.devicePixelRatio || 1;
canvas.width = Math.floor(viewport.width * dpr);
canvas.height = Math.floor(viewport.height * dpr);
canvas.style.width = `${viewport.width}px`;
canvas.style.height = `${viewport.height}px`;
canvasContext.scale(dpr, dpr);

// Render
await pdfPage.render({
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