RFR: 8234920: Add SpotLight to the selection of 3D light types [v14]

[Kevin Rushforth]

On Thu, 15 Apr 2021 02:21:50 GMT, Nir Lisker <nlisker at openjdk.org> wrote:

>> Added a SpotLight only to the D3D pipeline currently.
>> 
>> ### API discussion points
>> 
>> - [X]  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.
>> 
>> - [X] 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?
>> 
>> - [ ] The current implementation uses an ad-hoc direction property (using a `Point3D`). It crossed my mind that we could use the rotation transforms of the node to control the direction instead, just like we use the translation/layout of the node to get the position (there is an internal Affine3D transform for lights, not sure why `AmbientLight` needs it). Wouldn't that make more sense? When I rotate the light I would expect to see a change in direction.
>> 
>> ### Implementation discussion points
>> 
>> - [ ] I've gotten advice from a graphics engineer to treat point lights as spot lights with a 360 degrees coverage, which simplifies a few places. We can still try to optimize for a point light by looking at the light parameters: `falloff = 0` and `outerAngle = 180`. These possible optimization exist in `ES2PhongShader.java` and `D3DMeshView.cc`, and in the pixel/fragment shaders in the form of 3 different ways to compute the spotlight factor (the `computeLightN` methods). We need to check which of these give the best results.
>> 
>> ## Performance
>> 
>> Testing 3 point lights and comparing this branch with `master` using a 1000 division sphere, 200 meshes, and 5000 meshes.
>> Using an AMD RX 470 4GB GPU.
>> 
>> In this branch, there is a possible CPU optimization for checking the light type and using precalculated values (in `D3DMeshView.cc` for d3d and `ES2PhongShader.java` for opengl). On the GPU, I tried 3 ways of computing the spotlight factor contributions (`computeSpotlightFactor`, `computeSpotlightFactor2` and `computeSpotlightFactor3`) trying out different branching and shortcuts.
>> 
>> ### Results
>> The CPU "optimizations" made no difference, which is understandable considering it will not be the bottleneck. We can remove these if we want to simplify, though maybe if we allow a large number of lights it could make a difference (I doubt it). I don't have a strong preference either way.
>> 
>> The sphere 1000 tests always gave max fps (120 on Win and 60 on Ubuntu).
>> 
>> **Win 10**
>> Compared with the `master` branch, this patch shows 5-10 fps drop in the mesh 200 test and ~5 in the mesh 5000 test. I repeated the tests on several occasions and got different results in terms of absolute numbers, but the relative performance difference remained more or less the same. Out of the 3 `computeSpotlightFactor` methods, `computeSpotlightFactor3`, which has no "optimizations", gives slightly better performance.
>> 
>> **Ubuntu 18**
>> The mesh 200 test always gave 60 fps because it is locked to this fps, so we can't measure the real GPU performance change.
>> The mesh 5000 test shows 2-6 fps drop from master, with `computeSpotlightFactor` > `computeSpotlightFactor2`  > `computeSpotlightFactor3` at in terms of performance (~2 fps difference each).
>> 
>> **Conclusion**: we can expect a 5 fps drop more or less with 3 point lights. `computeSpotlightFactor3` on d3d and `computeSpotlightFactor` on opengl gave the best performances.
>
> Nir Lisker has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Combined rotation and direction

I think the API as currently defined is what we want. Having an explicit direction vector, and then transforming that by the transform of the light is quite flexible in a natural and expected way. I took the existing [`LightMotion`](https://github.com/openjdk/jfx/blob/master/apps/toys/FX8-3DFeatures/src/fx83dfeatures/LightMotion.java) example program, and created a new `SpotLightMotion` program (attached). It's easy to programmatically point the light to the object you wish to illuminate (the sphere or cylinder, in this example). And once you do, rotation works naturally.

Here is the code that computes the spot light direction:


        final Point3D light2Dir = sphereTranslate.subtract(light2Translate);


No modification was needed to the existing rotation code. You can run the program and then press `]` to start the red light orbiting in a circle (sorry, no UI controls).
[SpotLightMotion.java.txt](https://github.com/openjdk/jfx/files/6524997/SpotLightMotion.java.txt)
[SpotLightMotion.diff.log](https://github.com/openjdk/jfx/files/6524999/SpotLightMotion.diff.log)

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