Setting photon color of instanced light?

[wannabeArtist]

Hello,

As an attempt to keep my thread names a little more relevant, I start yet another one, which is basically part 2 of another thread here:
viewtopic.php?f=15&t=705

I have a particle setup based on emFluid and I'm using instance shape node to turn my particles into lights. For a while I thought I had got it right, but taking a closer look now, it seems that my results were what I wanted but produced by error

I had accidentally duplicated my point cloud, with one of them instancing lights and the other not - and it somehow produces the results in the screenshot.

While this kind of works, what I would really like to do is to be able to influence the photon intensity and color of each instanced light in ICE - is this possible?

Thanks!

EDIT: the grain in the shot is on purpose, I lowered the photon search radius to 0,1 to see if they actually have color or not.

[wannabeArtist]

Hello again,

Slight progress, but then another dead end.

I managed to set photon color from my point cloud, but only if I set a constant value for it (set data). The good news is that it actually changes the color of the photons accordingly, even though I the light has been instanced before changing the color (in order of execution), it still affects the end result!

The only problem is, how do I pipe the particle color for the set data?

This is the message ICE gives when I try to do this in the obvious way (the missing link in the screen shot):

Input context supported: per Object
Output context supported: per point of "pointcloud.pointcloud"

Is there a way to just isolate the "plain color" out of it's context so it could be used here?

Thanks!

[wannabeArtist]

Hmm,

I think I get it now, there's no way to make this work, because each particle would have a different color in each frame and there's only one light, which is been instanced.

Is there a way of casting the particle shape? Like "get particle shape" and then convert that to whatever object?

[Hirazi Blue]

What happens if you plug an attribute shader into the softlight of the light itself?
I tried this with a color_attribute and it resulted in different colors for every instanced light...

[wannabeArtist]

Very interesting!

I tried that before today (and just checked again), but I couldn't get anything out of the drop down (attribute color) other than "use default value". It doesn't seem to "see" the particles.

You must have instanced the light differently - how did you do that?

[Hirazi Blue]

I basically followed the setup Stephen Blair shows in this post on his Support Blog:
using point light instances in ice

[wannabeArtist]

Amazing,

That's what I looked at too, as you posted the link the other time.

Somehow it just wont work with my tree (based on emFluid). I even tried taking it to another place, but no luck. I better try an empty tree next...

[wannabeArtist]

Ok,

I must be doing something wrong here.

I made a very simple test scene, with just a cube and a point light and then a point cloud that looks like in the screenshot.
The instance shape instances the point light (from the top level), hierarchy mode is at "object only", out-of-range is clamp and index is 0.

This produces the lights in the corners of the cube, but I still cannot get the attribute color node to show anything but the "use default value" option. I also tested instancing simple geometry and then I get the rest of the options in the drop down menu. Just not with a light!

Strange! Could this be a version thing? I'm using 7.01

[Hirazi Blue]

And the size is explicitly set to something > 0?

[wannabeArtist]

Right, the size is also above zero.

It also seems that the instance shape node is pretty picky too, those settings mentioned above are the only ones I have managed to use with lights. They render, but wont let me change the colors (with attribute_color).

[grahamef]

Strange! Could this be a version thing? I'm using 7.01

If I recall correctly, using the color attribute with instanced lights didn't work in v7. It was added later (but off the top of my head I don't remember when).

However, what Stephen is doing in the tree that he shows on his is adding differently coloured lights to a group, and picking the group members randomly to use as the instance shape. Would that workaround be useful for you?

[wannabeArtist]

Good morning,

Darn, if it's really missing from 7.01, then that settles it.

I'm afraid the workaround wouldn't work in this project either. It is a fire simulation and I was hoping to control the light color by particle color, or in fact, the temperature of the light.

I think I'm reverting back to plan A and doing this with FG instead. Of course, I'm still very interested in hearing suggestions to make the photon idea work.

One thing that I was wondering myself was if there is a way of casting the "particle shape" into the object it instances? Like you would do in many traditional programming languages.

something like this (in fictional pseudo code):

Code: Select all

for(int i=0; i < particles.getCount(); i++)
{
   LightSource light = (LightSource)myParticles[i]; 
   // do stuff to light's attributes here
}

[Hirazi Blue]

Sorry for leading you on the wrong track...
I mistakenly assumed this was something 7.01 could do also & I couldn't remember either, when it was introduced...

Do the other attribute shaders work with instance lights?
If so, you might be able to "fake" it using custom attributes for RGB and mixing them back together in the Rendertree...

[wannabeArtist]

No matter,

I'm almost sure there would be a way to do this, if I weren't such a newbie with ICE

[wannabeArtist]

Just another idea: Is there a way in the render tree to "pipe" color from another material?

This way I could get the color for the lights from a regular object, which in turn gets the color from the particles...