Blended layers optimization

[RobertPieta]

📲 What

Added explicit background color to labels and other views that are rendered as blended layers.

🤔 Why

Labels and some other views by default have a transparent background, requiring iOS to render a blended layer. Reducing blended layers increases performance by reducing the work iOS needs to do when drawing and can have a large impact on scrolling smoothness and frame rate.

🛠 How

Added explicit background color to labels and some other views using the existing configuration conventions in the project. When applicable, the background color was updated in an aggregate styles variable or assigned from a styles object.

✅ Acceptance criteria

[ ] Unit and screenshot comparison tests pass

[justinswart]

hey thanks for the suggestion @RobertPieta! I will get our CI to run tests on this and chat to the team about it!

[dusi]

Thanks @RobertPieta ! We'll try to keep an eye on this more rigorously 🔬

[justinswart]

@RobertPieta I've enabled tests to run on your fork so that we can work to get this merged.

[dusi]

@RobertPieta as Justin mentioned, he has enabled CircleCI to run the tests against your branch (we've previously only been able to do that locally for public PRs).

In order for us to being able to merge, would it be possible for you to update all the failing Snapshot tests?

You should be able to resolve this by following these steps:

1. Select iPhone 8 as the destination device (our tests run against iPhone 8 devices only)
2. Run the test suite (CMD+U) in order to see all the failing tests
3. Re-record any failing tests

This could be done by going to a failing test / or a failing test class and turning the recordMode flag ON.

So for example recording new snapshots for the BackerDashboardProjectsViewControllerTests failing test would be as simple as running all of the BackerDashboardProjectsViewControllerTests tests with recordMode = true

// BackerDashboardProjectsViewControllerTests.swift
override func setUp() {
  super.setUp()
  AppEnvironment.pushEnvironment(mainBundle: Bundle.framework)
  UIView.setAnimationsEnabled(false)

  // Run tests once in record mode ... then remove and next time you run the tests they should pass
  self.recordMode = true
}

(this will unfortunately have to be manually done for all the failing test classes.

These new snapshots will have to be committed and pushed to the repo (and be part of this PR) in order for CircleCI to pass.

Setting background colours explicitly isn't visually different to a naked eye, but Snapshots tests treat this fact as a change so the snapshot has to be re-recorded.

ps: I believe you might also need to rebase/merge master in order to resolve possible merge conflicts. We have shipped some major changes after you've opened this PR.

Let me know if you have any questions.

[dusi]

Also (just for our future reference) I'm posting this comment to reference the changes done with this PR (for better illustration)

Before	After

[justinswart]

Thanks @dusi for the detailed explanation. @RobertPieta the simplest way to re-record all of the snapshots is to put the line that @dusi mentioned, self.recordMode = true in setUp() in TestCase.swift which is the superclass for all of our snapshot tests.

https://github.com/kickstarter/ios-oss/blob/master/Library/TestHelpers/TestCase.swift#L29

[dusi]

Thanks again @RobertPieta .

I've double checked that this PR doesn't break any visual functionality (more specifically the following):
✅ Classic Invert works
✅ Smart Invert works
✅ UI remains identical to human eye

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Tested on iPhone X (iOS 12.1.4)