Examples: Simpler atmosphere approach in webgpu_compute_birds

[mrdoob]

Related issue: #29334

Description

Instead of MeshStandardMaterial and HemisphereLight we can do the sky atmosphere with a simpler colors gradient with TSL.

@sunag My first real TSL experience 😇

Not sure how I feel about these chainable methods...

This ends up reading better to me:

add( 1.5, positionLocal.y )

Compared to this:

positionLocal.y.add( 1.5 )

Specially with sub()...

positionLocal.y.sub( 1.0 )

If I write that, but I decide I want to do 1.0 - y I feel limited...

This seems simpler and more flexible:

sub( 1.0, positionLocal.y )

Edit:

Hmm... But then by reading the code in #29354 ...

const pulse = pcurve(
	sin( hash( instanceIndex ).mul( PI2 ).add( timerGlobal( 0.5 ).mul( PI2 ) ) ).mul( 0.5 ).add( 0.5 ),
	0.25,
	0.25
).mul( 10.0 ).add( 1.0 );

I can see it ends up more compact.
But we end up with a language that has two reading directions...🤔

[sunag]

I think some redundancies are positive. In fact, we have redundancy in practically every type of language, such as in JS when creating conditionals, variables, functions, etc.

In my experience, chainable tends to be more readable for large lines of code and more efficient for drafting since it doesn't need to import new methods. I think both have their qualities and can be used by different user profiles. For example, I would use positionLocal.y.oneMinus().

This will certainly get better when we have Operator Overloading