Vector3.unproject(): Avoid computing inverse

[WestLangley]

As suggested in #14685 (comment).

...plus it removes another annoying cyclic reference in the build. :-)

In some examples, Vector3.unproject() is recomputing the matrix inverse every frame.

I think we are safe making this change now, but we need to be careful when using projectionMatrix.copy().

@Mugen87 What do you think?

[Mugen87]

I think it's okay to do this change since we also assume in Vector3.project() that camera.matrixWorldInverse is in sync with the world matrix of the camera.

[WestLangley]

@Mugen87 Search for projectionMatrix.copy and notice where it is used without copying the inverse, too. This is what I was referring to...

[Mugen87]

I see what you mean. In the examples, the copy happens in Reflector, Refractor, Water and CubeTexturePass. And in StereoCamera and CameraHelper which are located in the core.

It seems CameraHelper might need a small fix since it uses Vector3.unproject() in setPoint(). I guess we should add camera.projectionMatrixInverse.copy( this.camera.projectionMatrixInverse ); after the following line:

three.js/src/helpers/CameraHelper.js

Line 164 in f74563d

camera.projectionMatrix.copy( this.camera.projectionMatrix );

[WestLangley]

@Mugen87 I think we need this subtle change in the comment and code:

// we need just camera projection matrix inverse
// world matrix must be identity

camera.projectionMatrixInverse.copy( this.camera.projectionMatrixInverse );

[mrdoob]

Thanks!

[ghost]

I've isolated this PR as the one that breaks raycasting in my app.

I am using projectionMatrix.copy because I'm using a hybrid camera that transitions between the two. Any advice for how to fix this? Here's probably the most relevant part of my code

const matrixToCopy = this.isUsingOrthographicCamera ?
    this._orthographicCamera.projectionMatrix :
    this._perspectiveCamera.projectionMatrix;

this._hybridCamera.projectionMatrix.copy(matrixToCopy);

And the full file is here: https://gist.github.com/bleighb/83ff6814a7c8968425d48db0f580f442

[ghost]

Pinging @Mugen87 @WestLangley Any help would be greatly appreciated 😊

[WestLangley]

@bleighb This is not a help site. Please use the three.js forum instead.

[ghost]

Sorry about that. I'm not asking for handouts, it's just I took a good amount of time to isolate the exact commit that broke my app and I figured other people might be affected by this bug. Since you made the change, I thought the answer might either indicate that either there was a mistake on your part or I'm doing something terribly wrong 😄

[ghost]

I just fixed it by copying over the projectionMatrixInverse when I switch between camera types.

You mentioned before:

Thing is, projectionMatrixInverse is computed in updateProjectionMatrix() only; it is not set elsewhere. For example, it is not set whenever projectionMatrix.copy() is used. This will cause the matrix and its inverse to get out-of-sync.

We need to come up with an approach that will ensure they are synchronized if we want to make use of projectionMatrixInverse.

I believe this is what happened to me. The matrices came out of sync and it yielded weird side effects. I'm not asking for help anymore - I'm just trying to see if this is an issue or could be improved.

[WestLangley]

Good. You were able to solve the bug in your app yourself. I think the library is fine as is.

[funwithtriangles]

Thanks @bleighb for highlighting this, helped me with my own debugging!

For any 8th Wall users who have ended up here due to issues since r103, here's the fix:
https://gist.github.com/funwithtriangles/256de89332e438d8740301253ad9efd4