Prevent blank PDF exports for large Markdown documents by bounding html2canvas render scale

[Copilot]

Large Markdown documents could produce empty PDFs because the export pipeline attempted canvas captures beyond browser-safe limits; small files continued to work because they stayed below those thresholds.

• Root cause addressed: oversized canvas capture in PDF export

  • Added explicit safety bounds for PDF rasterization:
    • MAX_PDF_CANVAS_DIMENSION (per-side cap)
    • MAX_PDF_CANVAS_AREA (total pixel cap)
    • MIN_READABLE_PDF_SCALE (lower bound for legibility)
  • Computes a safeScale from document dimensions + bounds before calling html2canvas, preventing blank output from failed/invalid canvas allocation.

• Export capture now uses actual rendered element dimensions

  • Replaced fixed capture sizing assumptions with measured values from the offscreen export container (actualElementWidth, actualElementHeight).
  • Passes these dimensions into html2canvas (windowWidth, windowHeight) to keep pagination math and capture behavior aligned for long documents.

• Maintainability improvements in PDF export path

  • Centralized scale/limit constants near existing PDF page config.
  • Added targeted inline documentation for scaling fallback behavior and browser-limit rationale.

const dimensionLimitedScale = Math.min(
  MAX_PDF_CANVAS_DIMENSION / actualElementWidth,
  MAX_PDF_CANVAS_DIMENSION / actualElementHeight
);
const areaLimitedScale = Math.sqrt(MAX_PDF_CANVAS_AREA / (actualElementWidth * actualElementHeight));
const safeScale = Math.max(
  MIN_READABLE_PDF_SCALE,
  Math.min(desiredScale, dimensionLimitedScale, areaLimitedScale)
);

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Project	Deployment	Actions	Updated (UTC)
markdown-viwer	Ready	Preview, Comment	Apr 3, 2026 9:11am