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Just randomly testing what works. No issues detected with Light Passes.

The idea of light passes is to assign your lights in the scene to different layers with different "Light Pass IDs".
In postproduction you can then adjust after rendering how strong each pass should affect your final composition.

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You will find the official tutorial about Light Passes in OR standalone here:

viewtopic.php?f=51&t=44350

In general check out the official tutorial section to read up on OR features:
viewforum.php?f=51

But sometimes it is a bit tricky to figure out how those features are implemented in OcDS.
Therefore:
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A quick look at

Light Passes in OcDS:

You set the Light Pass ID in the Emission options of your light emitting diffuse material.
By default all lights are added to Light Pass ID 1.
You can manually assign lights to other Light Pass IDs to render them out on a separate layer.
Currently you can add your lights to any of eight different light passes.
Just assigning a light emitter to a Light Pass ID in the emission material options will not yet activate rendering of the pass.

In the OcDS Viewport in the tab "Render Passes" you will have to toggle on the Light Pass to activate rendering of the selected passes.

You can preview how each light pass looks like by clicking on the green L1 - L2 button on top of the OcDS viewport. In general all activated render passes are rendered simultaneously.
Export all your selected render passes
Composite your render passes in photshop with layer mode "Linear Dodge - Add"

The cool thing about rendering out Light passes is that you can change how strong each light should affect the scene AFTER you finished rendering by adjusting light strength in post production.
In this example the Light Pass 2 was dimmed down by reducing the layer opacity in photoshop down to 25%.
Of course you can also use masks in photoshop to get more control which areas of the image should receive more or less light.

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Added Light Passes.duf test scene as .zip

Happy rendering!

nice clear tuto; ty

Thanks for the Tutorial

Out of curiosity, should this slow render speed right down? I am rendering a scene now with 6 light ID's set, and it is rendering far slower than when i am not using light ID's

Also, interestingly, it doesnt seem to working my video cards quite as hard. They are not getting as hot as they usually do

Great tutorial - thanks for posting.

Paul

Nubblet wrote:
Out of curiosity, should this slow render speed right down? I am rendering a scene now with 6 light ID's set, and it is rendering far slower than when i am not using light ID's

Also, interestingly, it doesnt seem to working my video cards quite as hard. They are not getting as hot as they usually do

@ Render speed with passes
It seems rendering with 2 light passes activated slows render speed down around 4%.

Test Scene:
Kernel: PMC
Samples: 2'000

1min 23sec with 3GPU with default info passes and light passes
1min 20sec with 3GPU with just info passes

2min 4sec with 2GPU with default info passes and light passes
2min 0sec with 2GPU with just info passes

4min 3sec with 1GPU with default info passes and light passes
3min 54sec with 1GPU with just info passes

4min 14sec with 1 GPU with ALL passes activated.
Nevertheless in this test scene not all passes include information.
Most render out black because there is no scattering, transmission, refraction etc...

In this example you loose 4% render speed because of the light passes.
BUT
You might as well have saved the time to render the whole image a second time because you were not happy with the light set up.
Consider light passes as some kind of insurance that you do not have to rerender the whole image because of some minor creative differences caused by the look of one light.

Example:
Render time without light passes: 1h
Render time without light passes if you need to change the light in the scene and render a second time: 2h
Render time with light passes to make light adjustments in postproduction: 1h 2 min

@ VRAM differences with passes

Keep in mind that the temporary image is also stored in VRAM.
Eeach pass you activate will also need additional space in the VRAM.
The larger the resolution of your render the more space additional passes will need.

If you already are at the limit with spare VRAM activating render passes might cause textures to be stored out of core.

I do not know how this will be handled in OR3. Maybe then either the render passes or some geometry might get stored in normal system RAM?

In any case if you observe a larger reduction in render speed it could be because out of core memory storage was activated.

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Light passes as diagnostic tool

Even if you decide not to activate light passes in the final render they can still be of much help when adjusting the look of each light in the scene.
Often if you have multiple lights in the scene it gets challenging to figure out which light is contributing to the final result.
With light passes you can quickly fine tune the settings of one light by simply switching to its light pass without having to turn off the light emission of other lights in the NGE or the materials tab of OcDS:

Example workflow:
1) activate light emission on a surface
2) assign a light pass and activate it
3) switch the OcDS viewport to the light pass
4) fine tune the light
5) switch the OcDS viewport to "Main Beauty Pass" to see the effect on the scene with all lights

if you want to add more lights to the scene repeat 1) to 5)
if you are not happy with the look of an already existing light repeat 3) to 5)

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