Skip to content

fix Quaternion.slerp for small angles #14349

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
merged 2 commits into from
Jun 26, 2018
Merged

fix Quaternion.slerp for small angles #14349

Changes from 1 commit
Commits
Show all changes
2 commits
Select commit Hold shift + click to select a range
4c6fcc8
fix Quaternion.slerp for small angles
mbredif Jun 22, 2018
dbe0720
normalize in Quaternion.slerp
mbredif Jun 25, 2018
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
14 changes: 8 additions & 6 deletions src/math/Quaternion.js
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -533,19 +533,21 @@ Object.assign( Quaternion.prototype, {

}

var sinHalfTheta = Math.sqrt( 1.0 - cosHalfTheta * cosHalfTheta );
var sqrSinHalfTheta = 1.0 - cosHalfTheta * cosHalfTheta;

if ( Math.abs( sinHalfTheta ) < 0.001 ) {
if ( sqrSinHalfTheta <= Number.EPSILON ) {
Copy link
Owner

@mrdoob mrdoob Jun 23, 2018

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Math.abs() is no longer needed?

Copy link
Contributor Author

@mbredif mbredif Jun 23, 2018

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

no : a square is always non negative !
do you prefer a update of this PR with a call to normalize() or a simply implementing slerp with a subcall to slerpFlat ?

Copy link
Collaborator

@WestLangley WestLangley Jun 25, 2018

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

If cosHalfTheta = - 1.00001 due to roundoff then sqrSinHalfTheta could be negative.

Copy link
Contributor Author

@mbredif mbredif Jun 25, 2018

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

I agree, but that is no longer an issue : negative sqrSinHalfTheta corresponds to cases where the cos is round off errors away from 1 or -1, which corresponds to tiny values of the sin, for which lerp makes sense. (it WAS however an issue as the sqrt was not guarded against negative values and would output NaN values...)


this._w = 0.5 * ( w + this._w );
this._x = 0.5 * ( x + this._x );
this._y = 0.5 * ( y + this._y );
this._z = 0.5 * ( z + this._z );
var s = 1 - t;
this._w = s * w + t * this._w;
this._x = s * x + t * this._x;
this._y = s * y + t * this._y;
this._z = s * z + t * this._z;

return this;

}

var sinHalfTheta = Math.sqrt( sqrSinHalfTheta );
var halfTheta = Math.atan2( sinHalfTheta, cosHalfTheta );
var ratioA = Math.sin( ( 1 - t ) * halfTheta ) / sinHalfTheta,
ratioB = Math.sin( t * halfTheta ) / sinHalfTheta;
Expand Down