Feature/arealights

[marklundin]

Implementation of LTC based area lights.

The PR adds a new light shape property on all light types that when set to pc.LIGHTSHAPE_RECT or pc.LIGHTSHAPE_DISK or pc.LIGHTSHAPE_SPHERE enables area lighting using Linearly Transformed Cosines. It supports both Diffuse, Specular and Clearcoat using the physical/standard material.

Lights can be controlled using the entity transformations together with light attributes such as intensity and colour.

diffuse materials

Non uniform glossy + diffuse materials

I expect there to be a few comments on this, but I thought I'd try this as a first attempt to start a discussion.

Open questions;

1. Luts - The LUT's required by the implementation are very large and are computationally expensive to generate at runtime.
   update: LUTs are currently optionally included as a javascript file - but this may change before we make this feature public.

2. Floating point texture - It currently uses a FP texture, which could be a half float depending on hardware
   update: Half Floats and 8 bit per channel textures are now supported - allowing this feature to run on all platforms

3. Banding - There's an issue with banding which is as expected which is more noticeable on rough materials. It could be good to add some blue noise dithering behind a flag at the end of the material, but this is a separate issue.
   update: This is yet to be addressed.

Next steps. I've left these open until the core implementation is done

1. Lightmapping
2. Other light shapes
3. Textured lights

Additional Notes:

1. Area light shadows are currently approximated with punctual light shadows - this should be improved in a subsequent PR.
2. Directional area light specular is currently approximated with positional area light calculations - this should also be improved.

I confirm I have signed the Contributor License Agreement.

Also, I'm not great at the Pull Request workflow, so apologies if I mess this all up :D

Fixes #774.

[willeastcott]

Yeah, this file is 310KB uncompressed and 97KB gzipped - so we'll have to figure out a good solution to mitigate this.

[marklundin]

I'll have to look into the overhead of generating this at runtime. I'm guessing it's not insignificant, but at least it could be non blocking

[marklundin]

For reference the Lut generation code is here https://github.com/selfshadow/ltc_code/blob/texture/fit/fitLTC.cpp

I've not looked into the complexity, but it could be a good candidate for a worker or potentially, maybe a wasm lib?

[willeastcott]

Yeah, a worker sounds like a good option. But it'd be good to get a feel for how long the code takes to execute as compiled C++.

[marklundin]

@willeastcott as per @mvaligursky's suggestion, I've removed the LUT's from the engine itself. It is now a separate dependency that can be copied into asset registry. I imagine there will be better ways of integrating this, but for the moment, I think this gives the most minimally invasive way of doing it, yet flexible enough to switch it up down the line.

I've also removed the explicit width and height from the area lights and rely just on the entity transformation, which makes the code a lot simpler.

There is also the case of adding a flag for allowing the quad to project both sides, but I've left this out for now and can submit this as part of separate PR.

[willeastcott]

Would be great to add a screenshot to the PR description.

[raytranuk]

Ah, also I have a demo scene here that should work with the custom engine

https://playcanvas.com/project/730762/overview/arealight

@marklundin - I took a look at the demo - great to see it working!

One thing I noticed is that there is a crash when shadows are enabled - I'm that aware shadows are not part of this PR, but ignoring the setting and not crashing would be preferable.

[marklundin]

Ah, also I have a demo scene here that should work with the custom engine
https://playcanvas.com/project/730762/overview/arealight

@marklundin - I took a look at the demo - great to see it working!

One thing I noticed is that there is a crash when shadows are enabled - I'm that aware shadows are not part of this PR, but ignoring the setting and not crashing would be preferable.

Ahh thanks for pointing this out. Yes I'm a little unfamiliar with all the different code paths, and I'm aware these all create different shaders, so I'll have to dig into this a little more

[kungfooman]

Just did a quick investigation, generating those two LTC lookup tables:

g++ fitLTC.cpp dds.cpp -o fitLTC.exe -I..\external\CImg -Dcimg_display=0

Started fitLTC.exe and it took several minutes (AMD Ryzen 5 at 3.6 GHZ)

Actual amount of numbers:

> ltc.g_ltc_1.length
16384
> ltc.g_ltc_2.length
16384

I thought that maybe the printing/exporting the lookup tables itself may require most of the time (IO), so I commented all cout and export functions, but it still takes minutes.

So I guess it boils down to compressing 32768 floats as best as possible or finding a quicker generation algorithm.

[marklundin]

Just did a quick investigation, generating those two LTC lookup tables:

g++ fitLTC.cpp dds.cpp -o fitLTC.exe -I..\external\CImg -Dcimg_display=0

Started fitLTC.exe and it took several minutes (AMD Ryzen 5 at 3.6 GHZ)

Actual amount of numbers:

> ltc.g_ltc_1.length
16384
> ltc.g_ltc_2.length
16384

I thought that maybe the printing/exporting the lookup tables itself may require most of the time (IO), so I commented all cout and export functions, but it still takes minutes.

So I guess it boils down to compressing 32768 floats as best as possible or finding a quicker generation algorithm.

That's good to know. From a cursory look it didn't seem that expensive but I presumed there was a logical reason why it was precomputed

[raytranuk]

Ah, also I have a demo scene here that should work with the custom engine
https://playcanvas.com/project/730762/overview/arealight

@marklundin - I took a look at the demo - great to see it working!
One thing I noticed is that there is a crash when shadows are enabled - I'm that aware shadows are not part of this PR, but ignoring the setting and not crashing would be preferable.

Ahh thanks for pointing this out. Yes I'm a little unfamiliar with all the different code paths, and I'm aware these all create different shaders, so I'll have to dig into this a little more

Adding && type !== LIGHTTYPE_AREA to this line:

engine/src/scene/forward-renderer.js

Line 1240 in dd3a106

if (type !== LIGHTTYPE_DIRECTIONAL) {

will probably stop the crash I was getting.

[mvaligursky]

I had a look and this looks good to me. I added few small comments. I'm approving this, but please wait for 1-2 more approvals before merging.

Additional comments:

1. please test this in local environment inside the Editor to make sure existing functionality is working as expected
2. create Editor issue if not already to expose shape property and add gizmo rendering for area light shapes
   • ideally we would expose area lights in the editor behind flag pretty early, to allow us to conveniently test this functionality more comprehensively

[raytranuk]

@marklundin - I updated your PR description to line up with the final implementation in the PR. Well done and thank you again for the contribution to the PlayCanvas engine.

[willeastcott]

Yeah, thanks for this awesome contribution @marklundin! It's so exciting to see this get merged. 😄 🚀

[marklundin]

Great news @willeastcott and @raytranuk, excited to see this land! Any timeline on editor support?

[willeastcott]

So timeline will be:

• Deploy v1.38.0 - guesstimate: 11th January, which should give us the previous week to test on our dev server.
• Develop Editor UI changes.
• Test Editor Area Light UI.
• Deploy Editor Area Light UI behind a flag. We'll whitelist you straight away. Maybe 18th Jan - but we'll keep you updated.

[willeastcott]

Note that once the engine is deployed, you'll be able to drive the new functionality in a script as a stop gap. 😄