RFR: 8234920: Add SpotLight to the selection of 3D light types [v26]

[Kevin Rushforth]

On Thu, 17 Jun 2021 00:38:56 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?
>> 
>> - [x] 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:
> 
>   Fixed method call in glsl shaders

I did a full test run on 5 different system, including manual tests on 4 of them:

Windows 10 w/ Intel graphics
Linux w/ NVIDIA graphics (no manual testing)
Linux VM guest running on Windows 10 host
Mac w/ discrete graphics
Mac w/ integrated graphics

No problems detected. All looks good.

I think there could be some additional tuning done for point lights, but that could be looked at in a follow-on fix.

I reviewed the CSR and it is ready to be Finalized.

I finished reviewing the shader code, and left a couple comments on the HLSL shaders.

modules/javafx.graphics/src/main/native-prism-d3d/hlsl/psConstants.h line 28:

> 26: // see D3DPhongShader.h
> 27: 
> 28: static const int numMaxLights = 3;

I know we only support 3 lights, but I note that the vertex shader structures in `vsConstants.h` also have room for 5, and that number was unchanged by this PR. Have you ensured that the mismatch won't cause any problems? Also, with this change to `numMaxLights` from 5 to 3, the register assignments for the light arrays are now off (in a way that won't cause functional problems, just wasted space).

I wonder if it's better to revert this change for now and deal with it in a follow-up issue? If not, I recommend to make the change from 5 to 3 more broadly.

modules/javafx.graphics/src/main/native-prism-d3d/hlsl/vsConstants.h line 58:

> 56: float4x3    mBones[MAX_BONES] : register(c35);
> 57: 
> 58: float4      gReserved240[16] : register(c240);

`gReserved240` is now at the wrong location (it should be 245), so if it were ever used it would be a problem. It should be updated to avoid confusion at least.

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