[Bug]: BrowserWindow backgroundColor doesn't work in Electron 14 and 15

[samuelmaddock]

Preflight Checklist

• I have read the Contributing Guidelines for this project.
• I agree to follow the Code of Conduct that this project adheres to.
• I have searched the issue tracker for a feature request that matches the one I want to file, without success.

Electron Version

14.0.0-beta.11

What operating system are you using?

Windows

Operating System Version

Windows 10 21H1, macOS 11.5.1

What arch are you using?

x64

Last Known Working Electron version

14.0.0-beta.10

Expected Behavior

Creating a BrowserWindow with the backgroundColor option results in the new window displaying that color behind the transparent WebContents.

Actual Behavior

Creating a BrowserWindow with the backgroundColor option results in the new window displaying a white background color behind the transparent WebContents.

Testcase Gist URL

https://gist.github.com/4256f388d41ef0d974645a11ab72b1fe

Additional Information

The problematic version was discovered using Electron Fiddle's bisect feature.
v14.0.0-beta.10...v14.0.0-beta.11

#30136 seems related

I'm not seeing this behavior in a testing build of current main (8007d01).

I'm looking into a fix, will update as progress is made.

[codebytere]

@samuelmaddock this appears to only be happening within a certain range 🤔 it works properly on 16.0.0-nightly.20210727 and beyond.

v16.0.0-nightly.20210726...v16.0.0-nightly.20210727

[andmm]

Same bug here on 14.0.0 final on win 7.

[samuelmaddock]

@samuelmaddock this appears to only be happening within a certain range 🤔 it works properly on 16.0.0-nightly.20210727 and beyond.

v16.0.0-nightly.20210726...v16.0.0-nightly.20210727

It's fixed after the introduction of #30193

[samuelmaddock]

This works:

electron/shell/browser/api/electron_api_web_contents.cc

Lines 1373 to 1378 in dd7aeda

	// Set the background color of RenderWidgetHostView.
	auto* web_preferences = WebContentsPreferences::From(web_contents());
	if (web_preferences) {
	std::string color_name;
	rwhv->SetBackgroundColor(web_preferences->GetBackgroundColor());
	}

This does not work:

-rwhv->SetBackgroundColor(web_preferences->GetBackgroundColor()); 
+rwhv->SetBackgroundColor(SK_ColorRED);

🤔🤔🤔

[samuelmaddock]

Sometimes on startup, you can see the correct background color set, then immediately gets replaced with a white background color. I believe initially it shows the native window color followed by the RenderWidgetHostView's background.

Setting the background to transparent allows the native window's background color to show up:

rwhv->SetBackgroundColor(SK_ColorTRANSPARENT);

#30193 may have actually broken web_preferences->GetBackgroundColor() causing it to always return a background color value of 0 (fully transparent). On Electron v16, the "fixed" background color we're actually seeing is the background of the native window.

[samuelmaddock]

The white background color is coming from the page background color defined in Blink: https://source.chromium.org/chromium/chromium/src/+/main:third_party/blink/renderer/core/exported/web_view_impl.cc;l=3049-3058;drc=98898daa2e8f46ff098cea1f2e218f8a8266c838

  // Use the page background color if this is the WebView of the main frame.
  if (MainFrameImpl())
    return page_base_background_color_;

To update this color, we need to call WebContents::SetPageBaseBackgroundColor(). This was reverted in #30136 which we'll need to pay special attention to with a fix.

[samuelmaddock]

#30777 will solve the problem for Electron 14 and 15. main will need a separate PR since the WebPreferences refactor makes the code quite a bit different.

[jkleinsc]

@andmm your comment was deleted as a violation of the Electron Code of Conduct. You may consider this an official warning.

Please do not interact with the project for 24 hours. After that, please look through your open issues and edit them to ensure they're entirely on-topic, and we can continue the discussion here about the best way to go forward.