Optimize PDF path algorithm by using RLE

[Shane32]

Cuts file size in half or so.

Summary by CodeRabbit

• New Features

  • None

• Refactor

  • Optimized QR code PDF export to reduce drawing operations and improve export/render performance, potentially producing smaller PDFs without changing visual output.

• Documentation

  • Updated summary to describe the optimized PDF path generation approach.

[coderabbitai]

Important

Review skipped

Review was skipped due to path filters

⛔ Files ignored due to path filters (1)

• QRCoderTests/TransposeVerificationTests.pdf_renderer.approved.pdf is excluded by !**/*.pdf

CodeRabbit blocks several paths by default. You can override this behavior by explicitly including those paths in the path filters. For example, including **/dist/** will override the default block on the dist directory, by removing the pattern from both the lists.

You can disable this status message by setting the reviews.review_status to false in the CodeRabbit configuration file.

📝 Walkthrough

Walkthrough

Refactors PDF path generation in QRCoder/PdfByteQRCode.cs to replace per-module 1x1 rectangle emission with run-length encoding per row, batching contiguous dark modules into single rectangle commands via a while-based scan. No public API changes.

Changes

Cohort / File(s)	Summary
PDF path generation (RLE consolidation) QRCoder/PdfByteQRCode.cs	Replaced per-module 1x1 rectangles with run-length encoded rectangles per row in CreatePathFromModules; switched inner loop to a while-based scanner that skips light modules and emits a single startX y runLength 1 re command per contiguous dark run; updated comments; internal-only behavior change.

Sequence Diagram(s)

sequenceDiagram
  autonumber
  actor Caller
  participant PdfByteQRCode
  participant CreatePathFromModules as CreatePathFromModules()
  Caller->>PdfByteQRCode: Request PDF path for QR matrix
  PdfByteQRCode->>CreatePathFromModules: Build path from module matrix
  loop for each row y
    CreatePathFromModules->>CreatePathFromModules: Advance x while modules are light
    alt dark run found
      CreatePathFromModules->>CreatePathFromModules: Record startX and runLength
      CreatePathFromModules-->>PdfByteQRCode: Emit "startX y runLength 1 re"
    else no dark modules
      CreatePathFromModules-->>PdfByteQRCode: Continue to next row
    end
  end
  PdfByteQRCode-->>Caller: Return consolidated PDF path
  note over CreatePathFromModules: Replaced per-module rectangles with RLE per-row

Loading

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Pre-merge checks and finishing touches

✅ Passed checks (3 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title Check	✅ Passed	The title succinctly describes the primary improvement of the pull request, which replaces per-module rectangle generation in the PDF path algorithm with run-length encoding (RLE), and it accurately reflects the main change without extra noise or ambiguity.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.

---

Thanks for using CodeRabbit! It's free for OSS, and your support helps us grow. If you like it, consider giving us a shout-out.

❤️ Share

• X
• Mastodon
• Reddit
• LinkedIn

_{Comment @coderabbitai help to get the list of available commands and usage tips.}