RFR: 8234920: Add SpotLight to the selection of 3D light types

[Nir Lisker]

On Wed, 9 Dec 2020 00:54:14 GMT, Kevin Rushforth <kcr at openjdk.org> wrote:

>> Similar to what I said about the falloff, I can remove the documentation, but I don't see a compelling reason to artificially limit the values. The equation is as described in the docs. If someone puts in values outside of physically realistic ranges they will still get whatever the equation spits out. Do you think that there would be a too-large surprise factor?
>> 
>> One thing to note is that the user can do the clamping themselves (or we can do it later if we don't commit in the docs), but if we clamp, the user can't unclamp.
>
> The main issue I have is that the specified equation matches the proposed implementation only for values that satisfy the range constraints: `0 <= innerAngle <= outerAngle <= 180`.
> 
> The reason for this is that the shader implementation compares cosines not angles, and clamps the result of the division rather than testing whether the angle is < inner or > outer. These are very reasonable implementation choices.
> 
> We have a few options that I can see:
> 
> 1. List the expected range, and specify that values outside the expected range are clamped on usage.
> 2. List the expected range, and specify that the results are undefined for values outside the expected range.
> 3. Describe the equation that is actually happening.
> 4. Implement what the equation actually specifies, even for out-of-range values. This would constrain the implementation and likely require extra if tests in the shader.
> 
> Option 4 makes no sense to me. I don't care for 3, since it is less easy to explain and understand, and it precludes other implementations that are equivalent for in-range values but might behave differently for out-of-range values.
> 
> So that leaves option 1 or 2 as workable options. I prefer option 1, although I'll admit we aren't consistent on this point: we let the implementation do whatever it will do with out of range color values for PhongMaterial or Lights.

I see.

I also dislike 3 and 4. I prefer 2, but if you are convinced that 1 is better I'll go with it.

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PR: https://git.openjdk.java.net/jfx/pull/334