Failed to export local image when using gaia theme

[AseiSugiyama]

When I export the following markdown with marp-vscode,

---
marp: true
theme: gaia
inlineSVG: true
---

<!-- _class: lead -->
# Sample Slide

---

# Sample Slide

![bg right fit](plate.jpg)

the result is this.

However, when I used default theme (drop the theme: gaia line), marp for VSCode exports local image correctly.

Sample markdown and image are here. https://github.com/AseiSugiyama/marp_test

I guess this issue is not caused by #134 , so I opened this new issue.

[yhatt]

We've confirmed reproducibility. Start finding out the root cause.

Probably marp-team/marp-cli#293 is pointing out a similar problem.

NOTE: inlineSVG is the constructer option for developer, not global directive for Marp / Marpit. Defining inlineSVG: true in front-matter is no meaning because our Marp Core is always enabling inline SVG mode.

[yhatt]

I'm guessing this bug comes from Chrome/Chromium. Marp internally converts HTML into PDF through installed Chrome.

I've confirmed there is often a broken advanced background image for inline SVG mode if printed the exported HTML to PDF through Chrome >= 85 on macOS. It happens in any theme, not limited to gaia theme.

• Chrome 86 (Chromium r800071: latest): ❌
• Chrome 85 (Chromium r782078): ❌
• Chrome 84 (Chromium r768783): ✅

I'll continue working for finding out the workaround.

[AseiSugiyama]

Thank you for your great work! I was able to make my work finished by exporting my slide as a HTML file and print it out as a PDF file. I'm very glad if my example files help to find the root cause of this issue.

[yhatt]

Reporting details to Chromium bug tracker helps to resolve the root cause.
https://bugs.chromium.org/p/chromium/issues

I found out the exported HTML in Marp CLI with bare template can render background images correctly. We were supposed to have designed the default template (bespoke) also can convert to PDF, but probably injected scripts to control presentation might be prevented some background image rendering since Chrome 85.

We will implement to Marp CLI the fallback of using bare templatewhen running Chromium-based conversion.