Color emoji is not converted from pptx

[hiroshisuga]

Describe the bug
Color emoji is not correctly converted from a pptx file.

To Reproduce
Steps to reproduce the behavior:

1. Start a meeting
2. Upload a pptx presentation with color emojis.
3. Emojis do not show up

Used pptx file:
emoji.pptx

Expected behavior
Emojis show up.

Actual behavior
White rectangles (tofu) or monochrome emojis appear.

Screenshots

Additional context
Installing fonts-noto-color-emoji according to #11089 did not help. Likely a Libreoffice version problem.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[hiroshisuga]

This problem still persists on test24 server.

[antobinary]

Hi @hiroshisuga
Is this a font issue? Does it get resolved for you if you follow https://docs.bigbluebutton.org/admin/customize.html#add-custom-fonts-for-presentation-conversion or
Possibly related to #13319 ?

[hiroshisuga]

@antobinary , I will try to look more. I posted it quite a long time ago...

[gustavotrott]

Hello, it seems to be a known Libreoffice problem https://bugs.documentfoundation.org/show_bug.cgi?id=129523
I can reproduce a similar behavior, although for me the Emoijis are being removed instead of replaced by that wrong chars.

Using Libreoffice Desktop (on Ubuntu) I exported to PDF:

Result:

And in BBB I have the same result:

[gustavotrott]

It is also visible when exporting Shared Notes or moving it to Whiteboard:

[gustavotrott]

Libreoffice will not release a fix next days..
As a workaround, not perfect, but better than before:

We can remove the font fonts-noto-color-emoji that comes with Debian, and install this one as replacement https://github.com/adobe-fonts/noto-emoji-svg

sudo apt remove fonts-noto-color-emoji

wget https://github.com/adobe-fonts/noto-emoji-svg/releases/download/2.100/NotoColorEmoji-SVG.otf
wget https://github.com/adobe-fonts/noto-emoji-svg/releases/download/2.100/NotoEmoji.otf

sudo mv NotoColorEmoji-SVG.otf /usr/share/fonts/
sudo mv NotoEmoji.otf /usr/share/fonts/

fc-cache -v

Results after that:

emoji.pptx:

[gustavotrott]

Currently BBB is using LibreOffice 7.3.7.2 30(Build:2) (Alpine 3.17.2).
I did a test using LibreOffice 7.5.1.1 50(Build:1) (Alpine 3.18_alpha20230208).
It seems to be a little better but doesn't solve the problem yet.

emoji.pptx:

adobe-fonts/noto-emoji-svg is still the best strategy to mitigate the issue so far.

[gustavotrott]

Further testing has revealed specifics about the issue at hand. The problem arises during the process of converting a PDF to a PNG image.

Here's a breakdown of the issue:

1. Generation of PDF with LibreOffice: The initial PDF is created using LibreOffice, where emojis are correctly displayed in color.

   

2. Conversion of PDF to PNG with pdftocairo: The problem occurs when the pdftocairo tool is used to convert the PDF into a PNG image. The command used is as follows:

pdftocairo -r 300 -png -singlefile -scale-to-x 2048 -scale-to-y -1 -q -f 1 -l 1 /tmp/test.pdf /tmp/testc

This command results in emojis being rendered in grayscale, not in color.

3. Testing Conversion with pdftoppm: To isolate the issue, the same PDF file was converted using pdftoppm using the following command:

pdftoppm -png /tmp/test.pdf /tmp/testp.png

The pdftoppm tool successfully preserved the color of the emojis, confirming that the issue lies specifically with pdftocairo.

This detailed analysis indicates that the color loss issue during the conversion process is linked specifically to the use of pdftocairo. Alternative tools like pdftoppm do not exhibit this problem, suggesting an inherent issue with pdftocairo's rendering.