Puppeteer fix for creating blank (off page) screenshots

[thumpmaster]

Following to the conversation from this pull request https://github.com/garris/BackstopJS/pull/808/files, I've added the puppeteerOffscreenCaptureFix feature flag.

Could you please consider merging this as soon as you can? Thanks for this.

[cactusa]

HI @garris this is one of my colleagues finishing the PR I started months ago. As previously discussed this wraps the fix in a feature flag so it doesn't break any of you existing tests until you have the time to look into it in depth. This should enable us to run backstop in our CI pipeline in the meantime. Thank you again! Let us know if you's like us to make any changes to the PR.

[garris]

Thank you for the commit! I will attempt to push this today.

[cactusa]

Thank you very much!

[garris]

This is published to npm with the @beta tag. This branch also has some refactored code on it. Please validate when you get a chance -- if it's working for you I can push to latest. Cheers!

npm install backstopjs@beta (with optional -g flag)

[cactusa]

Ok would that beta version also work for Docker? Would Docker be pointed to that beta version specifically or would it only work with the latest backstop version?

[garris]

I expect it would work.

[cactusa]

We have tested this and it doesn't work in docker. It works just fine when it's not run in docker. I suspect that the docker image still pulls the latest version of backstop and ignores the beta branch.

[thumpmaster]

@garris Running the tests outside of the docker works fine.

[garris]

Hi guys -- I think I know the issue. I just pushed the tag with your fix to github. I had forgotten to do that before.

When BackstopJS is run with the --docker flag, backstop should ask docker to pull down the docker image corresponding to the same BackstopJS version that is running locally. This should be the case even when running @beta. Unfortunately-- I forgot to publish the tag with your fix before. Please give it another try and please send terminal output if it still doesn't work. Cheers!

[cactusa]

Thanks for that, will get back to you tomorrow!

[cactusa]

Everything has been tested and works as expected on the beta version with or without docker. Would you be able to give us an estimate of when you'll be able to make an official release of this?

[garris]

Fantastic! I will do ASAP. Hopefully today or tomorrow AM.