Nebula

In this tutorial, we are going to show you how to create a nebula with Phoenix. Since a nebula is a giant cloud of dust and gas in space, we will simulate it as smoke and then we will add lights to give it the appearance of a nebula. After simulating with a single Simulator, we will duplicate it into six instances. For better rendering performance we will render the scene using V-Ray GPU.

The simulation requires Phoenix 4.30 Official Release and V-Ray 5 Official Release for 3ds Max 2017 at least. You can download official Phoenix and V-Ray from https://download.chaos.com. If you notice a major difference between the results shown here and the behavior of your setup, please reach us using the Support Form.

The Download button below provides you with an archive containing the start and end scenes.

Download Project Files

Scale is crucial for the behavior of any simulation. The real-world size of the Simulator in units is important for the simulation dynamics.

Large scale simulations appear to move slower, while mid-to-small scale simulations have lots of vigorous movements.

When you create your Simulator, you must check the Grid rollout where the real-world extents of the Simulator are shown. If the size of the Simulator in the scene cannot be changed, you can cheat the solver into working as if the scale is larger or smaller by changing the Scene Scale option in the Grid rollout.

The Phoenix solver is not affected by how you choose to view the Display Unit Scale - it is just a matter of convenience.

As the focus of this tutorial is a large-scale simulation, setting the units to Meters is a reasonable choice.

Go to Customize → Units Setup and set Display Unit Scale to Metric Meters. Also, set the System Units so that 1 Unit equals 1 Meter.

The initial scene setup consists of the following elements:

1. Torus Knot geometry used for the smoke source.
2. Phoenix Fire/Smoke Simulator (PhoenixFDFire001).
3. Phoenix Fire/Smoke Source emitting Smoke from the Torus Knot geometry.
4. Omni 001 light for lighting.
5. V-Ray Camera 001 for look-development rendering.
6. PHXTurbulence for adding variation to the Smoke's motion.

The final scene setup consists of the following elements:

1. Five instances of Phoenix Fire/Smoke Simulator (PhoenixFDFire002 ~ 006).
2. Two more Omni lights (Omni 002 and Omni 003) for lighting.
3. Circle shape.
   
4. V-Ray Camera 002 for final rendering, the camera is path constrained to the Circle shape.
5. PCloud particle system used as stars.
   

The geometry used for the smoke emission is a Torus Knot. To give it a more organic look, we have applied a Noise modifier to it.

Go to Modify Panel → Create → Geometry → PhoenixFD → FireSmokeSim.

The exact position of the Phoenix Simulator in the scene is XYZ: [ -2.0, 0.0, -0.17 ].

Open the Grid rollout and set the following values:

Select the Phoenix Simulator → Output rollout and enable the output of Smoke, Wavelet, and Velocity Grid Channel. 

Select the Phoenix Simulator → Go to Scene Interaction rollout. Add the PCloud to the exclusion list. 

Create a Phoenix Fire/Smoke Source in the scene: Modify Panel → Create → Helpers → PhoenixFD → PHXSource.

Press the Add button to choose which geometry to emit and select the Torus Knot entry in the Scene Explorer.

For PHXSource:

Set the Emit Mode to Surface Force, Outgoing Velocity to 1.0 and Smoke to 4.0. Disable the Temperature option.

Set the Simulator → Simulation rollout → Stop Frame to 38.

Here is a Preview Animation of the simulation up to this step. It looks a bit dull now. It isn't anything like a nebula at all.

Create Helpers → Phoenix FD → PHXTurbulence.

Position to XYZ: [ -2.5, 9.0, 14.0 ].

Set the Strength to 350.0 and the Size to 30.0 m.

Reduce the Fractal Depth to 1.

Set the Decay type to Inv square.

Then go to the Fire/Smoke Simulator and run the simulation again.

Here is a Viewport Preview showing the result of the simulation so far.

Once the simulation is complete, go to the Phoenix Simulator → Input rollout.

For this tutorial we need only a static nebula, switch the Time Bend Controls Mode to Cache Index. Set the Direct Cache Index to 38.0.

Go to the Fire/Smoke Simulator → Rendering rollout, click on Volumetric Options.

For the Fire rollout, set the Based on option to Disabled.

For the Smoke Color rollout, set the Based on option to Smoke. Adjust the color gradient as shown in the image.

For the Smoke Opacity rollout, set the Based on option to Smoke. Adjust the curve as shown in the image.

Alternatively you can simply load up a Rendering Preset from the nebula_rendering_preset.tpr file that is provided in the sample scene.

Since we are going to render a very heavy volumetric scene, we will use the V-Ray GPU as our renderer.

The scene contains only three omni lights. To speed up rendering of volumetric effects, go to V-Ray Settings → Global Switches → Adaptive lights drop-down to Full Lights Evaluation.

Here is a test rendering up to this step. 

Select the Phoenix Simulator. Disable the Gravity since a nebula supposedly forms in outer space. Change the Conservation Method to Buffered, with a Quality of 40. Set the Steps Per Frame to 2. The Buffered method has the weakest conservation strength and shortest range, but produces nice details. For in-depth information, check the Conservation documentation.

Here is a test render up to this step. We can see a better pattern formation, compared to the results with default Dynamics settings.

Open the Phoenix Simulator → Resimulation rollout and enable Grid Resimulation.

Note that when you enable Resimulation, Phoenix will try to read the cache files for preview and rendering from the Resimulation Output Path, instead of the 'regular' Output. Don't worry if the Viewport goes blank and the preview disappears - you can always go back to the original cache files by disabling the Resimulation.

Set the Amp.Resolution to 0.2. This parameter is used to increase the resolution of the grid during the Resimulation process.

Set Amp. Method to Wavelet Nice and Wavelet Strength to 1.0.

Press Simulator → Simulation rollout → Start to begin the Resimulation.

Here is a test render up to this step. As you can see, after the Resimulation, we got more details in the smoky cloud, while maintaining the overall pattern formation from the base simulation.

With the Phoenix Simulator selected, hold down the Shift key and using the Move Tool drag the Simulator to the side. Then in the Clone Options set the object type to Instance. Number of Copies to 5. Press OK.

Now we have six Phoenix Simulators in the scene (PhoenixFDFire001~006).

Now move and rotate the Simulator instances in the scene, arrange them as the screenshot on the right.

Switch the render camera to V-Ray Camera 002. It is the camera that moves along the circle shape.

Here is a test render up to this step. With six Simulators in the scene, we can see the nebula now expanding to a larger region.

To make the image more interesting, turn on the other two Omni lights (Omni002 and Omni003) in the scene.

Here is a test render up to this step. Now both the lighting and volumetric simulation are ready for final rendering.

To render out the stars, unhide the PCloud in the scene, then proceed to the next step.

Open the V-Ray Frame Buffer and use the Create Layer icon to add layers for Lens Effects, White Balance, Curves, Color Balance and Filmic tonemap.

The image is rendered using the V-Ray Frame Buffer with the color corrections and post effects set to:

Filmic tonemap:

• Type - Hable;

• Shoulder strength: 0.670;

• Linear strength: 0.070;

• Linear angle: 0.490;

• Toe strength: 0.270;

• White point: 7.880.

Color Balance:

• Cyan-Red: -0.090;
• Magenta-Green: -0.026;
• Yellow-Blue: -0.082.

Curve: (as shown in the screenshot)

White Balance:

• Temperature: 5429.100

Lens Effects:

• Size: 11.110;

• Intensity: 0.500;

• Bloom: 0.500;

• Threshold: 0.570.

Feel free to use other values for the post effects depending on your preferences.

Alternatively you can simply load up a Rendering Preset from the nebula_VFB.vccglb file that is provided in the sample scene.

To further enhance the realism of the nebula, select the Phoenix Simulator, go to Rendering rollout → Volumetric Options. In the Smoke Opacity rollout, set the Absorption Constant Color to RGB (91, 96, 55).

Here is the final image. You can see additional details in the nebula color thanks to the smoke absorption color settings.

And here is the final rendered result.