Different output from Vector3::rotated in godot-rust vs GDScript

[robmikh]

I'm following along with this tutorial while porting the GDScript code to Rust. I ran into a difference in the output of Vector3's rotated function between Rust and GDScript.

I think it stems from a difference in how Godot and godot-rust handle the multiplication of a Basis with a Vector3:
https://github.com/godot-rust/godot-rust/blob/0413391002a1e824a36a7b012ce45774204eae3b/gdnative-core/src/core_types/geom/basis.rs#L585-L592
vs
https://github.com/godotengine/godot/blob/12e0f10c74e9619262f1edcfdc1840432ada0565/core/math/basis.h#L313-L318

I was able to resolve my issue by changing the implementation to match Godot's:

impl Mul<Vector3> for Basis {
    type Output = Vector3;

    #[inline]
    fn mul(self, rhs: Self::Output) -> Self::Output {
        Self::Output::new(
            self.elements[0].dot(rhs), 
            self.elements[1].dot(rhs), 
            self.elements[2].dot(rhs)
        )
    }
}

[robmikh]

I have a repro here:
https://github.com/robmikh/squash_the_creeps-rs/tree/issue751-repro
The interesting bit is here, which is a simplified version from the tutorial:
https://github.com/robmikh/squash_the_creeps-rs/blob/f75284d66566c3dde318a5769c68ff1dcd6a1fb7/src/mob.rs#L33-L38

In this branch is what I hope is the equivalent GDScript:
https://github.com/robmikh/squash_the_creeps-rs/tree/issue751-gdscript
https://github.com/robmikh/squash_the_creeps-rs/blob/b9d025a1c84e7c3f80a19d9c075dc1027a7f6966/Mob.gd#L16-L20

There is also a branch consuming a fix:
https://github.com/robmikh/squash_the_creeps-rs/tree/issue751-fix

This is what happens when using godot-rust:

This is what happens when using GDScript or branch issue751-fix:

Thanks for the report! Godot transposes the elements in Basis, which complicates things a little bit. It does seem that the xform implementation is broken given the C++ code, but the function is also tested against an output value (presumably) from Godot, so I wonder if from_euler is also broken here. Would be great if someone with more experience with the 3D parts could look into this.

[jo32]

I created a pull request to make sure the result of "rotated" is the same as it is in GDScript, another workaround to solve your problem. #760