Case 00354

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pptxgenjs Compatibility Skill

Generate PowerPoint-compatible PPTX files using pptxgenjs without triggering repair dialogs.

The Core Problem

pptxgenjs has 6 known defects (GitHub Issue #1449) that cause PowerPoint to show the "problem with content" repair dialog. The defects are baked into the library's XML generation and cannot be avoided at the JavaScript level. A mandatory post-processing step is required after every PPTX generation.

Workflow

Step 1: Generate PPTX with Safe API Patterns

When writing pptxgenjs code, follow these rules to minimize (but not eliminate) compatibility issues:

Forbidden APIs (will cause cross-version issues)

❌ shadow — generates complex OOXML effect chains unsupported in many PowerPoint versions
❌ transparency — inconsistent behavior across PowerPoint/WPS/LibreOffice versions
❌ String shape names like "oval", "roundedRectangle" — writes invalid prstGeom values

Safe Alternatives

✅ Use line borders instead of shadow for visual depth
✅ Use pre-mixed colors instead of transparency (calculate blended colors on dark backgrounds)
✅ Pre-render dimmed icon variants (dark PNG) instead of runtime image transparency
✅ Always use enum constants: pres.shapes.OVAL, pres.shapes.ROUNDED_RECTANGLE

Pre-mixed Color Calculation

To replace transparency on a dark background, calculate the blended color:

background #1A1A2E + white at 20% opacity → approximately #3A3A4E

For dimmed icons, render at design time with a dark color:

const iconDim = await iconToBase64Png(FaShield, "3A4450", 256);  // dark variant

Step 2: Post-Process with fix_pptx_compatibility.py

This step is MANDATORY. Even with perfect API usage, pptxgenjs generates invalid XML that must be fixed.

Run the bundled script:

python scripts/fix_pptx_compatibility.py <input.pptx> [output.pptx]

If output is omitted, the input file is overwritten in place.

The script fixes all 6 known defects:

1. Phantom slideMaster overrides in [Content_Types].xml — the #1 cause of repair dialogs. pptxgenjs registers non-existent slideMaster2~N.xml for every slide
2. Invalid theme font references — replaces +mn-lt, +mn-ea, +mn-cs, +mj-lt, +mj-ea, +mj-cs with Microsoft YaHei
3. dirty= attribute — removes non-standard pptxgenjs attribute
4. p14:modId elements — removes non-standard namespace elements
5. Notes Slides/Masters — removes broken notes files and their relationship references
6. Zero-extent shapes and empty elements — fixes cx="0" cy="0", <a:t></a:t>, <a:ln />

Step 3: Verify

Open the PPTX in PowerPoint to confirm no repair dialog appears. For automated verification, check:

• All Override PartNames in [Content_Types].xml point to existing files
• No +mn-lt style font references remain
• No dirty= attributes remain
• No p14: namespace prefixes remain in slide XMLs

Common Mistakes to Avoid (Lessons from Real Incidents)

1. Don't assume shadow/transparency fixes are enough — The real root cause is usually phantom slideMaster overrides in Content_Types.xml, not visual effects
2. Don't write validation scripts with max() fallback to 0 for -1 values — This causes false positives in element order checks
3. Don't use single-line regex for XML that spans multiple lines — Use re.DOTALL flag
4. Don't skip post-processing — Even if the PPTX looks fine in your version of PowerPoint, it may break in others
5. Search for known issues FIRST — Before diagnosing compatibility problems from scratch, check GitHub Issues for the library

Reference

For the complete list of pptxgenjs defects with examples and fixes, see references/pptxgenjs-pitfalls.md.

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