feat!: New `AlternatePattern` argument for `SequenceEffect`

[TheMaverickProgrammer]

• This PR fixes math in MoveToEffect so that negative progress did not reflect the direction of the delta offset vec.

• Corrected progress getter overload in SequenceEffect to correctly map to the progress when _index < 0.

• Added onStart() in recede() initial condition so that effects like MoveToEffect can recalculate their initial data.

• Removed unnecessary math in DurationEffectController to avoid potential negative zeros.

• Introduced a new type AlternatePattern which allows users to include or exclude the last effect in the sequence when the pattern reverses. NOTE: When playing forward, the last effect is List.last, but in reverse it is List.first.

• Default value is now AlternatePattern.repeatLast.

• Made the TiledGame example project more aesthetically interesting.

  • The camera now pans to all 4 corners WRT the bounds of the loaded map and uses the new AlternatePattern feature along with all the new fixes.

• [x] I have followed the Contributor Guide when preparing my PR.

• [ ] I have updated/added tests for ALL new/updated/fixed functionality.

• [x] I have updated/added relevant documentation in docs and added dartdoc comments with ///.

• [x] I have updated/added relevant examples in examples or docs.

TO DISCUSS

1. I have skipped the test checkbox until I had a review and we could discuss these changes.
2. We may need to consider an onEnd() for Effects. Or provide onStart() with an initial progress value to calculate from.

Breaking Change?

• [ ] Yes, this PR is a breaking change.
• [x] No, this PR is not a breaking change.

Related Issues

I looked but didn't immediately see anyone reporting these issues. I discovered them myself.

[TheMaverickProgrammer]

There's still the topic to discuss: I'm in favor of providing onStart() with an initial progress value to calculate the starting conditions from since MoveEffect can be affected by bounds checks.

[TheMaverickProgrammer]

@spydon

In the case that dProgress becomes negative it is supposed to go backwards. Say that the previous progress is 0.9 and it it supposed to move backwards to 0.8, then dProgress should be -0.1, not 0.1.
Try running only the the MoveToEffect with alternate: true.

Please try running the tiled_example/lib/main.dart example with from my PR and compare it with the same example in upstream after adding the ViewportAwareBounds to the camera in the upstream version. From our conversation, this issue seems to be missed and it's crucial to understanding the problem that is being addressed with the addition to onStart() in the recede() function and using a non-negative duration value.

[spydon]

I'll give it a proper try when I'm back home again next week!