SpotLight: rectangular spot light shape

[nipmarsh]

This PR add the possibility to change the spot light shape from Circle to Rectangular

[Mugen87]

Um, I don't think it's a good idea to support different shapes in a hard coded way. #13057 seems to be more promising. Also note #14621.

[nipmarsh]

Um, I don't think it's a good idea to support different shapes in a hard coded way. #13057 seems to be more promising.

I saw it but it is completly inactive for a while now... Maybe i can create a new type of light call RectangularSpotLight?

[Mugen87]

What if someone wants a TriangularSpotLight^^? It seems this approach does not scale very well...

[nipmarsh]

What if then someone wants a TriangularSpotLight^^? It seems this approach does not scale very well...

I've just implemented what was suggested by @mrdoob in this comment #13057 (comment)

Regarding this comment, this PR seems to be a good idea.

Also a filter map could be added for creating any shape ;-)

[Mugen87]

I think your approach is too limited. Using a texture in the sense of Cookies is much more flexibel, IMO.

[WestLangley]

I think that cookies are the best way to model the "barn doors" on studio lights. I would prefer to go the cookie route.

[Mugen87]

@nipmarsh Thanks for your work on this but it's better to focus on #14621 instead.