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

[Nir Lisker]

On Thu, 22 Oct 2020 18:29:19 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.

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