[Rev 03] RFR: 8217472: Add attenuation for PointLight

[Kevin Rushforth]

On Sat, 18 Apr 2020 15:45:32 GMT, Kevin Rushforth <kcr at openjdk.org> wrote:

>> I discussed this with a graphics engineer. He said that a couple of branches do not have any real performance impact
>> even on modern mobile devices, and that, e.g., on iOS 7 using half floats instead of floats was improving shader
>> execution dramatically. Desktops with NVIDIA or AMD and even Intel modern cards can process dozens of branches with no
>> significant performance degradation.  He suggested actually to have all the light types in a single shader file
>> (looking ahead here). He also suggested not to permute on shaders based on the number of lights and just pass in a
>> uniform for that number and loop over it. The permutations on the bump, specular and self illuminations components are
>> correct (not sure we are not doing that for the diffuse component). If we add later shadows, which is not on my near
>> to-do list, then we should permute there.  It also depends on our target hardware. If we take into account hardware
>> from, say, 2005 then maybe branching will cause significant performance loss, but that hinders our ability to increase
>> performance for newer hardware. What is the policy here?  I have a Win10 laptop with a GeForce 610M that I will test
>> this weekend to see if the mobile NVidia cards have some issue.
>
> I think most of those are good suggestions going forward. As for the performance drop, the only place we've seen it so
> far is on graphics accelerators that are a few years old by now. Integrated graphics chipsets (such as Intel HD) either
> old or new seem largely unaffected by the shader changes. What we are missing is performance metrics from newer
> graphics accelerators on Mac and Windows.  Even with the performance drop on older graphics devices, I'm leaning
> towards not having the shaders to be shaders to be doubled, since this is an artificial stress test with huge quads. If
> we could get performance data from a couple more recent graphics accelerators that would be best.

Here is a slightly modified test program. It fixes a compilation error in the previous, and also adds a system property
to set the number of quads:

It creates 200 quads by default. If you need to increase this or decrease it to get something in the ~ 10 fps range you
can do that with `-DnumQuads=NNNN`.

[pointlighttest.zip](https://github.com/openjdk/jfx/files/4526179/pointlighttest.zip)

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PR: https://git.openjdk.java.net/jfx/pull/43