Colour cloud via external shader(& rainbow rehash)

[bigben]

Hi All

I'm not going to have a lot of time to work on this, but I came across the TGD from my rainbow test from a few years back (http://www.planetside.co.uk/forums/index.php?topic=3517.0) and thought I'd see if a slightly different approach. might work. The attached image is a very rough test render that is supposed to be a terrain and normal clouds (low fractal octaves for speed), with a green mist in front of it.

My original rainbow model used a hack of low cloud density combined with a high colour value to prduce a coloured cloud.  3 masked clouds of red, green and blue were then superimposed to produce to produce the full spectrum.  This experiment attempts to colour a cloud via an external surface shader in the hope of using a single cloud for the colours of the rainbow.
1. The colour is created by converting a colour to RGB scalars, multiplying them by a constant scalar and then re-building the colour (in this case R0 G200 B0)
(previously done by setting the cloud colour to green and then increasing the number to 200)
2. This is then added as a child of a surface layer, blended by the cloud's PF and then fed into the cloud node

For the most part it appears to be working except for the normal clouds in the background which are showing through with complementary colours. I'm open to any suggestions on the clouds settings to try if this is at all possible. The attached TGD was made partly by trial and error rather then any knowledge of the specific cloud settings.

If it works, I can then replace the single colour with the conical rainbow mask. The new deg<->rad conversions are handy and have cleaned up the model a bit.

Ben

[dandelO]

http://www.planetside.co.uk/forums/index.php?topic=10931.0
And ring constraints are indeed possible, as some recent posts have shown.

[bigben]

ooooo  very interesting looking image. I missed it in the search results because of the title of the first post.

Dissecting the clip file now.  Different method to mine but the clouds look good.  My approach is easy to animate as the entire rainbow moves with the camera. Only the heading and altitude of the sun have to be manually updated if the sun moves.

[Tangled-Universe]

You can add colour to clouds by replacing the cloud shader with a coloured powerfractal.

[bigben]

You can add colour to clouds by replacing the cloud shader with a coloured powerfractal.

But how do you set the colour of the PF to >1  .  I tried creating a spectrun using mogn's gradient first but the green was not cooperating. 

Anyway, it's probably about time I shared it too...

I played around with a twist of Mahnmut's idea, combining our 2 methods.

• second planet added at the camera position.
     
  
  
  • distance of rainbow then controlled by cloud altitude and thickness
  • easy to move planet with camera for animations
  • looking vertically through the clouds avoiding possible altitude-related banding effects (just guessing here but it seems better in this regard)
• additional tweaks to "rain" PF to reduce noise and increase coverage which in turn required lowering cloud colour values which in turn will require some tweaking of the gradients (particulary the green and edges of the primary rainbow)
• The "non-rainbow" rain has been disabled as I deleted part of the mask and will have to re-crreate it.

Low res render below and the TGD. (just replace my terrains with a PF)  The network is still a bit messy and I still don't remember exactly what everything does but I'm getting there.  It's all spread out for development but should compact pretty well. Feel free to play and if you make any improvements or have any suggestions, post them back here please.

One possible tweak under consideration was adding additional cloud layers for yellow and cyan, mainly to smooth out the secondary rainbow when it gets faint. It's not 100% mathematically accurate but it's reasonably close. Primary and secondary with lightening inside primary and outside secondary.


Ben

[Tangled-Universe]

I'm not sure what you mean Ben. You can have a colour >1 just by typing in a larger number.
Or, for the blue node fetisjists, add a multiply colour function after the powerfractal

[bigben]

Or, for the blue node fetisjists, add a multiply colour function after the power fractal

... The first image above has a grey cloud with a colour PF, but this produces odd effects with the clouds behind (pink in the first image) but not the landscape. The idea was there but it doesn't seem to be compatible with the lighting of the cloud model in TG unless there's some setting that avoids this. If it's possible it should mean being able to use a single cloud layer which in turn should speed up rendering.

In the second image the colour is defined in the cloud node.  The high number makes it visible with the low density when it is lit, but in the shadow of an object or another cloud it "disappears" because of the low density. I think it was Matt that put me on to that hack.

The only colours I could set in the cloud node had to have RGB values at either 0 or 255 before increasing the colour number above 1 i.e. red, green, blue, yellow, cyan and magenta. Any other colour would turn to white when the number was increased.

Here's a render at detail 0.4  Renders a LOT faster than my original model although I think a lot of it was due to tweaking  the PF for the rain.

[bigben]

With only the rainbow being rendered you can see what happens when the it passes into the shade. Note the absence of colour at the top of the rainbow. With the full model there would also be cloud around the rainbow (simulating the rain)

[TheBadger]

Thanks for the file Ben. Wanted to see into one of these.

[bigben]

Adding in 3 more cloud layers for the complementary colours.

Setting up the gradients is pretty basic math. Getting the cloud density, colour and response to direct light/shadow is the tricky bit.
* At very low densities (resulting from low values in the mask) the colour disappears, disrupting the smooth blending.  That's why there are extra nodes to change the gradient to a range between 0.5-1.  A suitable hack for RGB but for a 6 colour setup it would require an additional mask.. trying to do without it for now.[edit] Nope. it's needed[/edit]
* Make the cloud too dense and the colour persists in the shade
*Cloud colour too light the saturation drops, too dark and it just looks wrong (and increases the risk of banding)

Loaded a photograph into Photoshop to measure the colour bands to make the colour distribution a bit more realistic. Running a test render on a primary rainbow (render times are back up with the extra cloud layers)

[bigben]

Here's a small render of the 6 cloud version. It does produce a better gradation of colours and the problems confirm the workings of this hack.
* Note the banding/gaps in the rainbow near the top.. this will be reduced by making the mask range from 0.5-1 instead of 0-1 (or at least increasing it to something above 0)  I had increased the cloud coverage by a small amount to try and compensate for this in this render but that was a bad idea.
* Increasing the mask minimum value will in turn improve some of the blending down at the bottom of the rainbow and hopefully soften the outer edges. The masking is there for it but it's rendering too sharply
* You can also just see the continuation of the inner lightened "rain" at the very top right. This area is shaded and it shouldn't be visible so I'll have to drop the density of that cloud.

I'll have to fix the mask range first before tweaking anything else, although increasing the magenta colour value is looking like a prime candidate. Something for next weekend 

[bigben]

One last quick test rendered overnight.  Extended the range of the mask for each colour to the next colour of the same type. e.g. Green drops to 0 where Red and Blue = 1, Cyan drops to 0 where Yellow and Magenta = 1

Detail 0.75, AA 4, default GI

[dandelO]

This looks good, Bigben, and I imagine you could get much better render times now with the option to ray trace the atmosphere than you were before in those old rainbow test threads. I know there's been some debate about the speed/quality ratio of using RTA over standard rendered atmospherics but, because I'm such a skinflint for render time, I usually manage to juggle the customiseable AA sampling to get a huge increase in speed(only in some instances, of course) over the default rendering method.

I've been thinking, and I'll test in a bit... In one of these threads linked here, I was able to create the full spectrum with only one atmosphere node, instead of several clouds, and now, with the fantastic 'shadow funtion' option in the atmosphere, I think I might be able to constrain the visibility of that single atmosphere to a disc using altitude constraints and a transform shader to rotate those constraints onto the vertical, one node is far easier to piss around with than loads of coloured clouds. Hmmm...

* I also see Simius Strabus is making great progress with rainbows recently, too. We've found a few ways now that semi-work with convenience but there must be a nice, simple solution to this, juggling 7 clouds is a bit of a long way round, I think. An atmosphere with the spectrum contained within one node is something I'm pretty interested in playing with again.

[bigben]

The render times are much better now

The idea behind my original model was that it should be reasonably realistic, particularly for animations. Thus, using a cloud to simulate the distribution of rain,  you can get a rainbow to show the variations in the cloud density and thickness. Since this model projects a conical mask outwards from the camera the density of the rainbow will vary with the thickness of rain (that is in sunlight) penetrated. Doing this with a thin disc would be very difficult. ... and a drawback of this is that you have to restrict the range of distances from the camera (previously done with a distance shader, now done with cloud altitude and thickness in the secondary atmosphere) If you don't restrict the range then the combined brightness of the rainbow all the way to the horizon can look odd.

In my first test scene for example the rain surrounds the butte so the rainbow is fainter in front of it because the rest of the rain is obscured by the terrain.

The one flaw with the current model I'm working on is that it doesn't observe the cloud altitude restrictions on the primary planet, so this would have to be defined separately. I'm thinking the rainbow model should not use an internal density shader for the cloud, but rather generate a full density rainbow which is then masked by the density shader of whatever cloud is being used to simulate the rain. This would also make it a much more portable model.

Juggling 7 cloud layers is indeed tricky for building the model, but once the right balance is found (if it can), then no more juggling should be required in use.

Once built most of the network doesn't need to be visible. Required inputs would be:

• altitude and heading of the sun
• position of second planet (if using this model, = camera position)
• connect the density shader used for rain
• probably output a mask for the rain density shader to obscure the rain replaced by the rainbow... (hmmm that gives me an idea)
• altitude range for rain
• relative intensity of secondary rainbow

In theory, once it's set up it would be very easy to animate as it simply follows the camera, always placing the rainbow in the correct location whenever it intersects with "rain".  I'm happy to consider any cloud colouring model people want to share
Checking Simius Strabus' posts, the gradation looks good and is probably easier in many situations, although it needs the math to get the right diameter and thickness (40-42° radius if you please) .

[bigben]

Slowly discovering more useful cloud settings. Most of the extra smoothness in this image was a result of tweaking the cloud settings and then readjusting the colour intensity to compensate for the change in density.  I think this is getting pretty close and I have an idea for the violet end of the spectrum to try. The very faint top end is very nice now and I can almost live with the break up of the yellow and red about 2/3 up.

Most threads of the various rainbow attempts seem to at least have in common the need to add some extra density on top of colouring some clouds.  My initial model added it to the colour mask but I'm doing it now with an additional cloud. I'm currently doing this via an additional cloud layer but in the end this additional density will come from the cloud layer targeted by the rainbow via a density mask that cuts the rainbow out of the cloud.