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

[Kevin Rushforth]

On Mon, 26 Oct 2020 00:43:02 GMT, Nir Lisker <nlisker at openjdk.org> wrote:

>> Added a SpotLight only to the D3D pipeline currently.
>> 
>> ### API
>> 
>> 1. Added `SpotLight` as a subclass of `LightBase`. However, it could also be a subclass of `PointLight` as it's a point light with direction and extra factors. I saw that `scenario.effect.light.SpotLight` extends its respective `PointLight`, but it's not a perfect analogy. In the end, I think it's a questions of whether `PointLight` will be expanded in a way which doesn't not suit `SpotLight`, and I tend to think that the answer is no.
>> 
>> 2. The inner and outer angles are the "diameter angles" as shown [here](https://docs.microsoft.com/en-us/windows/win32/direct3d9/light-typeshttps://docs.microsoft.com/en-us/windows/win32/direct3d9/light-types).  I, personally, find it more intuitive that these are the "radius angles", so half these angles, as used in the spotlight factor formula. Do you think I can change this or do you prefer the current definition of the angles?
>> 
>> CSR will be created when the API review is finished.
>> 
>> ### Implementation
>> 
>> I've gotten advice from a graphics engineer to treat point lights as spot lights with a 360 degrees coverage, which simplifies the shader a lot and removes branching over the light type. This is covered anyway by a possible optimization in the pixel shader, which I've noted in an inline comment, that skips the spotlight computation if `falloff` is 0 (this is the case for non-spotlights).
>> 
>> ### Performance
>> 
>> Testing 3 point lights in order to compare with the [pre-patch performance](https://github.com/openjdk/jfx/pull/43#issuecomment-600632114):
>> 
>> Without the falloff == 0 branching:
>> sphere 1000 subdivisions: 120
>> mesh 5000: 9.5
>> mesh 200: 111.5
>> 
>> With the falloff == 0 branching:
>> sphere 1000 subdivisions: 120
>> mesh 5000: 9.3
>> mesh 200: 112.5
>> 
>> Ubuntu 20:
>> With the patch:
>> Mesh 200: 60 fps
>> Mesh 5000: 15 fps
>> Sphere 1000: 60 fps
>> 
>> Without the patch (master branch)
>> Mesh 200: 60 fps
>> Mesh 5000: 16.3 fps
>> Sphere 1000: 60 fps
>> 
>> So no major changes. I will repeat these tests to make sure there was no mistake.
>
> I suggest we start with looking at the API and the subclass question. This will unblock the CSR process.

My preference would be for `SpotLight` to subclass `PointLight`. I also somewhat prefer the 1/2 angle (radius) rather than diameter to specify the spread angles (inner and outer).

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