[Core] Allow different gravity vectors in Nodes

[alxbilger]

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Reviewers will merge this pull-request only if

• it builds with SUCCESS for all platforms on the CI.
• it does not generate new warnings.
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• it does not generate new scene test failures.
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[hugtalbot]

[ci-build][with-all-tests]

[hugtalbot]

Interesting change @alxbilger
The Gravity component is available for this. But your change should make it more straightforward, I will give it a try

[hugtalbot]

Tested and approved 👍

What do you think @alxbilger about setting gravity to "0 0 0" as default value?

[alxbilger]

What do you think @alxbilger about setting gravity to "0 0 0" as default value?

I think it will break a lot of scenes

[alxbilger]

I also think about creating a graph link instead of a simple copy:

if (!worldGravity_.isSet())
{
    worldGravity_.setParent(&c); ///< Gravity IN THE WORLD COORDINATE SYSTEM.
}

What do you think?

[hugtalbot]

I think it will break a lot of scenes

I like it baby 🚒 🔥

I also think about creating a graph link instead of a simple copy:

🤔 why would you do that? I am unsure about side effect

[hugtalbot]

I also think about creating a graph link instead of a simple copy:

why @alxbilger

[alxbilger]

So that it can update if its parent has changed

[hugtalbot]

To be noted, this change would only work in XML : SimpleAPI or Python do not change the "isSet" property as does the XML. I investigate on this currently

[hugtalbot]

If #4911 is solved, then #4910 could replace this PR @alxbilger

[damienmarchal]

@hugtalbot, isSet is switched to "true" at first value change (eg: any begin/write edit). Can you explain a bit what kind of behavior should be expected ?