marp2pptx 0.1.2

Convert Marp Markdown files to polished PPTX presentations

Marp PPTX Post-Processing: Status & Next Steps

1. Marp HTML Structure (Key Concepts)

Slides:

• Each slide is represented by a <svg data-marpit-svg ...> element.
• Inside each SVG, there are one or more layers, each as a <foreignObject> with width/height attributes.
• Each <foreignObject> contains a <section> element, which holds the content for that layer.

Headers:

• If a slide has a header, a <header> element is placed under the <section> element.
• Split background images are never placed in the header.

Marpit Advanced Backgrounds:

• Advanced backgrounds (true and split) are always placed in a <div data-marpit-advanced-background-container="true">.
• This div can contain one or more <figure> elements, each with a background image.
• The direction (horizontal/vertical) is set by data-marpit-advanced-background-direction.
• Split backgrounds are indicated by attributes like data-marpit-advanced-background-split on the <section>.

2. What We're Trying to Achieve

We want to post-process a Marp-exported PowerPoint (.pptx) so that all background images specified with Marp’s advanced image syntax are visually correct in the exported .pptx. This includes:

• True backgrounds (![bg](...)): Fill the slide, appear behind content, and match Marp’s CSS background-size/position logic (cover, contain, auto, etc.).
• Multiple backgrounds (![bg](...) x N, with horizontal/vertical): Stack images in the correct order and direction, matching Marp’s advanced backgrounds.
  • Split backgrounds (![bg left], ![bg right], ![bg left:33%], etc.): Place the image as a foreground element in a defined region (not as a slide-wide background), shrinking the content area as Marp does. Only left and right split directions are supported (not top or bottom).
• Cropping and placement: All cropping, scaling, and placement (e.g., right:35%, left:38% 70%, w:100% h:50%) should visually match Marp’s HTML/PDF output.

Reference: Marpit image syntax documentation

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3. What We've Done So Far

• HTML Parsing:

  • The script parses Marp HTML output, extracting slide backgrounds, split info, image URLs, and layout instructions, by walking the SVG/foreignObject/section/container/figure structure.
  • It builds a slide model for PPTX generation, replacing the old markdown/image logic.

• True Backgrounds & Multiple Backgrounds:

  • Images fill the slide or are stacked horizontally/vertically, matching Marp's stacking logic.

• Advanced Background Scaling:

  • Implemented full support for Marp's background-size property, parsed from the generated HTML.
  • Supported keywords: cover (fills the area, cropping if necessary), contain and fit (scales to fit within the area), auto (uses original image size), and percentage values (e.g., 50%, which scales the image relative to the container).

• Split Backgrounds:

  • Split backgrounds (left, right, with percentage) are placed in the correct region and cropped to fill only the split space. Only left and right split directions are supported.
  • Multiple images in a split region are distributed equally within the split space (always horizontally), matching Marp's stacking logic.

• Debugging and Logging:

  • Extensive debug logging shows all image shapes, sizes, and the matching process for troubleshooting.

• Robust Image Mapping: Refactored the processing logic to map all images from the Marp HTML (including headers, content, and backgrounds) one-to-one with the picture shapes in the PPTX slide. This ensures that transformations are applied only to the correct background shapes, preventing unintended modifications to other images on the slide.

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4. CLI & Pipeline Automation

The script has been refactored into a full command-line interface to automate the entire Marp to post-processed PPTX pipeline.

• End-to-End Automation: The script now orchestrates the three main steps of the conversion process:
  1. HTML Generation: It calls npx @marp-team/marp-cli to convert the source Markdown file into an HTML file.
  2. Initial PPTX Generation: It uses the same CLI tool to create a raw, editable PPTX file (*_raw.pptx).
  3. Post-Processing: It runs the existing background image processing logic on the generated HTML and raw PPTX files.
• File Management:
  • Smart Naming: Automatically creates an intermediate _raw.pptx file and saves the final output as <input_name>.pptx.
  • Automatic Cleanup: Deletes the intermediate HTML and _raw.pptx files by default to keep the workspace clean.
  • Keep Intermediates: A --debug flag is available to prevent cleanup for debugging purposes.
• Improved Usability:
  • CLI Arguments: The script now uses argparse for robust handling of command-line arguments, including the input file, output file, and other options.
  • Help Documentation: A --help command provides clear instructions on how to use the script and its available options.
  • Enhanced Typing: Static typing has been improved throughout the codebase for better maintainability and reliability.

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5. Testing

The new CLI simplifies testing significantly. To process a Marp Markdown file, run the script with the input file path.

Set the name of the Marp markdown file:

$MARP_MARKDOWN_FILE = "sample.marp.md"

Run the end-to-end processing pipeline with a single command:

uv run marp_pptx_postprocess.py ./${MARP_MARKDOWN_FILE}

The script will handle the intermediate steps and produce a final, post-processed PPTX file named sample.marp.pptx.

To inspect the final output:

explorer "${MARP_MARKDOWN_FILE}.pptx"

To run the pipeline and keep the intermediate files for debugging:

uv run marp_pptx_postprocess.py ./${MARP_MARKDOWN_FILE} --debug

This will leave the following files for inspection:

• ${MARP_MARKDOWN_FILE}.html
• ${MARP_MARKDOWN_FILE}_raw.pptx
• ${MARP_MARKDOWN_FILE}.pptx (final output)

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6. Next Steps (Advanced Placement)

Recent Progress

• Implemented a fix to widen all text boxes by 4cm (1133 pixels) to prevent unwanted text wrapping in headings when viewed in LibreOffice.
• This adjustment ensures that headings display correctly without wrapping issues.

The next major step is to handle explicit width and height parameters for background images, which are specified in the markdown but not always available in the final HTML background-size property.

• Parameters to Support:

  • Explicit width and height: Keywords like width: 300px or h: 50%.
  • Shorthand w and h: e.g., w:300px.
  • Positional arguments: e.g. ![bg 50%] or ![bg 300px 200px]. The script will need to parse the original markdown to get these.

• Goal: Correctly position and scale images that use these markdown-specific parameters.

• Content Area Shrinking:

  • For split backgrounds, shrink the content area as Marp does, so content is not covered by split backgrounds.

Install and run tool

Run as module without installing:

python -m marp2pptx --help

Install locally and run:

uv pip install -e .

marp2pptx --help

to unsinstall:

uv pip uninstall marp2pptx