Three.js Update an object's position relative to another object's scale

Question

I dont know who needs to see this, just wanted to share a solution for a problem I encountered recently. I hope it helps someone.

Lets say you have an object House and inside that House you have another object Chair in a very specific spot. you scale the House's Size by 2, making it bigger. The Chair then is not at the same spot inside the House because the House's size is different. you need to move the chair to that very specific spot without doing it manually.

EDIT Moved the solution to an answer

Typically, you'd want to check the "Answer your own question - Q&A style! button when creating the question. Then, you would write your own answer, instead of posting the solution in the question itself. I would recommend moving the solution to an answer. — TheHaloDeveloper
– TheHaloDeveloper, Commented Jun 9, 2022 at 18:27
Of course making Chair a child of House, or scaling the parent would solve this. This is obviously for a case where you cant have that hierarchy. — javrro
– javrro, Commented Jun 13, 2022 at 15:18

javrro · Accepted Answer · 2022-06-09 19:54:18Z

1

this is the formula you would use: ( (Chair.position * House.scaleFactor) - (House.position * (House.scaleFactor - 1)) )

In Threejs code it would look something like this:

const scaleFactor = 2;
house.scale.setScalar(scaleFactor);
chair.position.set(
                    (chair.position.x * scaleFactor) - (house.position.x * (scaleFactor - 1)),
                    (chair.position.y * scaleFactor) - (house.position.y * (scaleFactor - 1)),
                    (chair.position.z * scaleFactor) - (house.position.z * (scaleFactor - 1))
                );

answered Jun 9, 2022 at 19:54

javrro

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