feat(physics): Interpolation

[joaomanita]

things

Description

Add Interpolated{} to entities to interpolate them.
Example in distance constraint sample.

Checklist

• Self-review changes.
• Evaluate impact on the documentation.
• Ensure test coverage.
• [ x] Write new samples.
• Add entry to the changelog's unreleased section.

[github-actions]

PR Preview Action v1.6.2
🚀 View preview at https://GameDevTecnico.github.io/cubos/preview/pr-1563/
Built to branch gh-pages at 2025-09-04 17:22 UTC. Preview will be ready when the GitHub Pages deployment is complete.

[codecov]

Codecov Report

❌ Patch coverage is 0% with 62 lines in your changes missing coverage. Please review.
✅ Project coverage is 51.60%. Comparing base (c1ec1e2) to head (20c626c).
⚠️ Report is 30 commits behind head on main.

Files with missing lines	Patch %	Lines
engine/src/interpolation/plugin.cpp	0.00%	53 Missing ⚠️
engine/src/physics/solver/integration/plugin.cpp	0.00%	6 Missing ⚠️
.../src/physics/solver/distance_constraint/plugin.cpp	0.00%	1 Missing ⚠️
...c/physics/solver/penetration_constraint/plugin.cpp	0.00%	1 Missing ⚠️
engine/src/physics/solver/plugin.cpp	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1563      +/-   ##
==========================================
- Coverage   51.98%   51.60%   -0.38%     
==========================================
  Files         497      500       +3     
  Lines       27029    27303     +274     
  Branches     2512     2557      +45     
==========================================
+ Hits        14051    14091      +40     
- Misses      12978    13212     +234     

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[RiscadoA]

Ty for working on this! Will be very very useful for online multiplayer too 👀
I'm not very familiar with the physics code, but I have two doubts regarding this implementation:

• why would Interpolated be optional? Shouldn't it always be used? I don't see a reason to use physics without interpolation.
• the whole interpolation mechanism should be independent from the physics plugin. It should be a separate plugin, outside the physics directory. Of course, the physics plugin would depend on it. This would allows us to use it for other stuff such as online multiplayer without necessarily enabling physics.

[fallenatlas]

Sorry for thanking so long to review and thank you for working on this! 🙏 Overall, I think this works well for what we want, I only have a couple concerns.

[fallenatlas]

Ty for working on this! Will be very very useful for online multiplayer too 👀 I'm not very familiar with the physics code, but I have two doubts regarding this implementation:

• why would Interpolated be optional? Shouldn't it always be used? I don't see a reason to use physics without interpolation.

I think it reduces the necessity of the dev knowing that exists at the start and yeah, ideally we'd always want it I think. I guess it isn't for the same reasons as the solver and stuff also isn't included with the physics which, tbh, I think we should also change those as it doesn't make a lot of sense.

• the whole interpolation mechanism should be independent from the physics plugin. It should be a separate plugin, outside the physics directory. Of course, the physics plugin would depend on it. This would allows us to use it for other stuff such as online multiplayer without necessarily enabling physics.

Having in account that fixed step is also not part of the physics plugin I think this would make sense yes. I'm worried about how it would work having multiple plugins writing to the same thing and having it work well. But, the biggest problem I see is that, this interpolation is strictly for fixedStep, if we had for example servers running outside of fixedStep I'm not sure if this plugin would be good for that.

[RiscadoA]

LGTM other than what I just pointed out!

[RiscadoA]

Any reason to not include reflection for the struct's fields?

[fallenatlas]

Just a couple more things.

Also, I have a doubt. Do we have a guarantee that Position is nextPosition when a fixedStep starts? We need it to make sure that the physics remain independent from the framerate.

[fallenatlas]

Are these comments meant to be here this?

[joaomanita]

What could be different? That there is no rotation interpolation yet?

[github-actions]

⚠️ Clang-Tidy found issue(s) with the introduced code (1/1)

[github-actions]

⚠️ readability-simplify-boolean-expr ⚠️
redundant boolean literal in conditional return statement

Suggested change

	if (timer.value >= step.value)
	{
	return true;
	}
	return false;
	return timer.value >= step.value;