The following question was originally posted on StackOverflow. However, the question has not been attended for a week, I would like to ask for help in this lua-filters repository.

I endeavour to modify the font colour within a pptx document that has been generated from a qmd file utilising a lua filter entitled 'color-text.lua', which is from 5.1 Font color | R Markdown Cookbook.

The lua filter demonstrates proficiency in altering the font colour during the rendering process of HTML-based documents, encompassing standard HTMLs and revealjs presentations, as well as latex-based documents, which encompass PDFs and beamer presentations.

Regrettably, I am uncertain about the methodology to enhance the lua filter's capabilities in order to alter font colour in pptx documents. Any insights or suggestions are appreciated.

MWE

test.qmd

---
format:
  pptx:
    keep-md: true
filter:
  - color-text.lua
---

## Slide title 1

First, we define a Lua filter and write it to
the file `color-text.lua`.

## Slide title 2

Now we can test the filter with some text in brackets with
the `color` attribute, e.g.,

> Roses are [red and **bold**]{color="red"} and
> violets are [blue]{color="blue"}.

color-text.lua

The following script is a modified version of color-text.lua that was originally posted on StackOverflow. I added a code block to modify pptx (xml) format (i.e. if FORMAT == 'pptx' then... return run) using ChatGPT (gpt-3.5) but the code block ignores [...]{color="..."} notation.

function Span(elem)
  local color = elem.attributes['color']

  -- If no color attribute, return unchanged
  if not color then
    return elem
  end

  -- Check if we are rendering to PPTX format
  if FORMAT == 'pptx' then
    -- Define the namespace for PPTX elements
    local pptx_ns = 'http://schemas.openxmlformats.org/drawingml/2006/main'

    -- Create attributes for the custom span element
    local run_attrs = pandoc.Attr(nil, {'color-text'})

    -- Create a run element for font color with attributes
    local run = pandoc.Span({}, run_attrs)
    run.content = elem.content

    -- Create attributes for the custom span element inside the run element
    local span_attrs = pandoc.Attr('pptx-font-color', {'pptx-font-color'}, { ['w:color'] = color, ['xmlns:w'] = pptx_ns })

    -- Add the font color as a custom attribute in PPTX namespace
    table.insert(
      run.content,
      1,
      pandoc.Span({pandoc.Str(' ')}, span_attrs)
    )

    return run
  else
    -- For non-PPTX formats, apply font color changes directly
    if FORMAT:match 'html' or FORMAT:match 'revealjs' then
      -- For HTML and Reveal.js, transform to <span style="color: red;"></span>
      -- Remove color attributes
      elem.attributes['color'] = nil
      -- Use style attribute instead
      elem.attributes['style'] = 'color: ' .. color .. ';'
      -- Return full span element
      return elem
    elseif FORMAT:match 'latex' or FORMAT:match 'beamer' then
      -- For LaTeX and Beamer, encapsulate in LaTeX code
      -- Remove color attributes
      elem.attributes['color'] = nil
      -- Add LaTeX code for font color
      table.insert(
        elem.content, 1,
        pandoc.RawInline('latex', '\\textcolor{' .. color .. '}{')
      )
      table.insert(
        elem.content,
        pandoc.RawInline('latex', '}')
      )
      -- Return only span content
      return elem.content
    else
      -- For other formats, return unchanged
      return elem
    end
  end
end

pandoc / lua-filters

[Question] How to improve a lua filter so that it can customise font colour of pptx documents #272

MWE

test.qmd

color-text.lua