spotLightHelper: fix duplicate rotation

[but0n]

When I rotate the parent of spot light, the cone of light helper will rotate twice.

Scene tree

• scene
  • spotLight group (transform control attach here)
    • spot light
    • target of spot light

Example

this.matrix = light.matrixWorld;

• The only thing this object need is the world position of the spot light, but this matrix here include world position and world rotation (not direction) of the light, so the helper will apply the world rotation matrix of the light.

this.cone.lookAt( vector2.sub( vector ) );

• this will also locally rotate the cone to the correct direction.

[WestLangley]

Do this, instead:

this.position.copy( vector );

[WestLangley]

SpotLightHelper is limited in that it only supports lights without rotated parents.

An advantage of this change is it eliminates this pattern:

this.matrix = light.matrixWorld;
this.matrixAutoUpdate = false;

If #14658 is merged, then this PR would have to be revisited.

/ping @mbredif

[mbredif]

/ping @mbredif

This is a quick and simple fix, I think it can be merged before the discussion on #14658 settles.

As a side note you could save a temporary Vector3 variable and a Vector3.copy call by replacing

var vector = new Vector3();
var vector2 = new Vector3();
[...]
vector.setFromMatrixPosition( this.light.matrixWorld );
vector2.setFromMatrixPosition( this.light.target.matrixWorld );
this.position.copy( vector );
this.cone.lookAt( vector2.sub( vector ) );

with

var target = new Vector3();
[...]
this.position.setFromMatrixPosition( this.light.matrixWorld );
target.setFromMatrixPosition( this.light.target.matrixWorld );
this.cone.lookAt( target.sub( this.position ) );

[WestLangley]

Thanks!

[mrdoob]

Do you still have the issue after #15320?

[but0n]

Nope, thanks!