Feature/particles view update

[eneim]

IMPORTANT:

• I commented out some lines in SplashActivity to make the sample, please read it and un-comment for normal behaviour.
• I'm using AS RC-1 so please manually change gradle plugin back to 2.2.3, or I will do it after the review.

Issue

• Current ParticlesAnimationView is beautifully implemented. But it comes with some trade off as follow:
  • Redundant Object allocation inside onDraw method: createLines(particles) uses Stream which will allocate new Iterators each calls. Furthermore it unnecessarily generates new Lines.
  • "Random" should be used once only to ensure the randomness of number. See its doc for more detail.
  • Current implementation of createLines(particles) will draw each line twice, which is not so good.
  • Calling drawLines to draw a single line is not so good too.
  • Private classes can be Private static class, to prevent leak (not now, just in case).

Overview: what I did

• Make private class (Particle, Line) static.
• Re-implement Line class, fix some step in Particle class that would allocate new objects in onDraw().
• Cache necessary objects as ParticlesAnimationView's member, and just update them if need (see Random instance, List instance for example).
  • This fix reduce the number of Line instance from few thousands (数万 lines in some cases) to 780 (= C(40, 2)) (see my comment).
• Improve onDraw and so on. Stream is no longer used here ...
• isShouldLinked is actually shouldBeLinked I think :D.

Discussion: so it worth the change?

• Current View is shown in few seconds, so there may be no need to do redundant work.
• But ... some may want to use it as Cover background, or Title view etc, so improving it here can help.
• See screenshot for more information (see number of GC calls, magenta (or blue?) in GPU log ...) (sorry don't know how to align 2 screenshot horizontally, please help).

  Screenshot

  Before	After

[konifar]

Thank you for contribution! Interesting!

[eneim]

Thanks. Let me fix the license and conflict in few minutes :D

[eneim]

FYI @konifar I would like to ask @roana0229 (author of this View) to review this if possible. My change may conflict with the expected behaviour in some unexpected ways.

[konifar]

Looks good. Thanks 😃 @roana0229 Can you review this?

[eneim]

@konifar my latest commit cause a failed build on circleci, checking it, turns out :app:testDevelopDebugUnitTest failed with one case. But running it on my machine passes all tests. Can you manually trigger a rebuild? If it keeps failing again I will try to figure out what happened.

[konifar]

Sorry, currently CI is not stable. I'll work on it tonight.

[eneim]

Thanks, just take your time :D

[roana0229]

LGTM 👍

[konifar]

Thanks for improvement!