New Feature: Low Quality Image Placeholder cont.

[aSouchereau]

Continues #2558 for #2258 including new frontend implementation.

Adds low quality image placeholder to be displayed while album covers are downloading.
Improves perceived loading times.

Approach:

• Adds new size variant of type 7 called 'placeholder'
• Adds PlaceholderEncoder class to compress image to usable size, convert to base64 and save to db
• Adds new standalone pipe to process the placeholder
• Adds step in legacy code path to process the placeholder
• Adds command to handle placeholders that exist but have not been encoded yet
• Adds diagnostic info check for determining number of missing and unencoded placeholders
• Adds maintenance option to generate missing placeholders
• Modifies SizeVariant getUrlAttribute to use data URI instead of app url for placeholders
• Modifies Thumb to include generated placeholder

Demo

[codecov]

Codecov Report

Attention: Patch coverage is 89.62963% with 14 lines in your changes missing coverage. Please review.

Project coverage is 84.82%. Comparing base (2001c44) to head (757cefe).
Report is 1 commits behind head on master.

Additional details and impacted files

[ildyria]

@aSouchereau can you squash the full branch ? So that you get all the credits when we merge. :)

[aSouchereau]

Oops, not sure if thats correct. All commits related to the placeholder feature are squashed. Everything else is the result of a previous merge commit.

[ildyria]

I fixed the conflicts.
Can you check if the check if the changes are as you wish. :)

[ildyria]

If so you can squash everything with :

# Do make sure that your master branch is up to date with current lychee master
git pull master
# soft reset the branch to master (keep the changes but place the pointer on master HEAD)
git reset --soft master
git commit -m " .... "
git push --force <origin> album-cover-placeholder

[aSouchereau]

If so you can squash everything with :

# Do make sure that your master branch is up to date with current lychee master
git pull master
# soft reset the branch to master (keep the changes but place the pointer on master HEAD)
git reset --soft master
git commit -m " .... "
git push --force <origin> album-cover-placeholder

Yes, looks good. Thanks for the help :)

[ildyria]

I replaced the hidden by animation-fadeOut animation-fill-forward so that the transition is nicer. :)