This tutorial covers the steps to creating realistic fire with V-Ray for 3ds Max.
Overview
VRayVolumeGrid is a special kind of volumetric effect that can render effects such as explosions, burning fuel, large scale smoke like from volcanoes, as well as dust, tornadoes, clouds, galactic nebulae and more. The volume grid reads the data from an input cache file (.aur, .vdb, or .f3d) which has been created in advance in another simulation software, e.g. Chaos Phoenix.
Here, you will learn how to load and render such pre-made input files (in this case containing a fire simulation) in VRayVolumeGrid, as well as how to control the volumetric parameters so that the fire looks more realistic.
The scene used for this tutorial contains a simple room setting. The closeup shot is taken with a V-Ray Physical Camera (set to Physical Exposure) that uses real-world camera settings for further realism. Most of the geometries are taken from the extensive Chaos Cosmos 3D assets library.
To download the .aur file used in this tutorial, click the download button below.
Preparations
To use VRayVolumeGrid you need a suitable input file with a proper volumetric data in it. In this case you need a fire simulation.
To learn how to create such a file using Chaos Phoenix, follow the steps from this tutorial: MAKING OF FIRE TRAILS
Creating the VRayVolumeGrid
- Create VRayVolumeGrid from the V-Ray menu (V-Ray > Create > Geometry > V-Ray VolumeGrid).
Alternatively, you can use the V-Ray VolumeGrid icon from the V-Ray Toolbar, the Create menu option, or the VRayVolumeGrid button from the Command panel.
- The Open window pops up upon the grid’s creation and prompts you to load a file. Select a file and load it.
The .aur file used here – Fire_Trail.aur – is a single frame, taken from the Making of Fire Trails tutorial (check the link in the Preparations section). You can download it from the Download Assets button.
If you accidentally close the Open window without loading a file, you can load it later from the Input rollout of the VRayVolumeGrid parameters. You can also use the VRayVolumeGrid without a cache file.
Positioning and Scaling the VRayVolumeGrid
The Fire_Trail.aur is bigger than the fireplace space, because it was simulated in a different scene for a different purpose. However, you can use it in whatever scene you want. For this purpose, just scale it to fit the case.
So let’s move and scale the VRayVolumeGrid to fit the fireplace space better. For smaller flames, you can position the file lower.
Here the volume grid is set as shown on the screenshot.
Note that the GPU Preview option is enabled from VRayVolumeGrid parameters > Preview rollout for enhanced viewport presentation.
Render the scene to see how the default parameters of the Fire_Trail look.
You can use the VFB Render Region option and IPR to quickly preview the result.
There’s too much smoke and the fire itself needs some more tweaks - mainly of the intensity and color.
Even though the final result of the Fire trails tutorial looks great, when importing the simulation cache in a new scene it looks nothing like it.
This is so because the simulation caches carry only the simulation data, but not the render settings.
The simulation data can be interpreted and rendered in many different ways - you can render the fire as mesh or the mesh as smoke.
If you wish to transfer the volumetric render settings from one scene or Volume Grid to another, you can save a preset with all the settings and export it to a file through the Render presets button in the Rendering rollout of the V-Ray Volume Grid.
Adjust the VRayVolumeGrid Parameters
- In the Rendering rollout, click the Volumetric Options… button to open the Volumetric Render Settings.
- In the Smoke Color rollout of the Volumetric Render Settings, disable the Base on option. This prevents the smoke from rendering.
Now, let’s adjust the fire color and intensity. You can use the available Fire_Trail.tpr preset file, which contains the final fire settings from the Fire trails tutorial as a starting point or set all the necessary parameters’ values manually from the Volumetric Render Settings.
To save time let’s just load the ready-made Fire_Trail.tpr file. Download the file from the Download Assets button.
- Go to the Rendering rollout and click the Render Presets… button.
- From the drop-down menu, select Load from File.
- Browse to the Fire_Trail.tpr file and load it.
Render settings aren’t stored within the caches themselves. You have to save and load them as Render Presets in a .tpr file format. Thus, you are able to use the same volumetric render settings across projects or simulators.
- Keep the Fire Opacity Mode to Fully Visible. This mode is intended to be used with Phoenix simulations, such as simulations with sources that emit Temperature but do not emit Smoke. However, keep in mind that this mode does not produce alpha. For more information, see the Render Fire page.
- Create new flags with their respective colors and positions in the Gradient Ramp as shown in the screenshot. The exact rgb values used here are:
first flag: rgb (0, 0, 1)
second flag: rgb (1, 0.065, 0)
third flag: rgb (1, 0.151, 0)
fourth flag: rgb (1, 0.286, 0.036)
fifth flag: rgb (0, 0.279, 1)
sixth flag: rgb (1, 0.64, 0.25)
- Render again.
Now the fire is less strong and needs a general intensity boost to light the surrounding environment.
- In the Fire rollout, increase the Fire Multiplier to 15. This makes the intensity stronger.
- Set the Light Power on Scene to about 50 to light the room around the fireplace.
Not the fire lights the rest of the objects in the room.
The fire intensity is even along the flames, so let’s tweak the gradient ramp a little further.
- Move the 5th point of the ramp to x=1580, y=-0.0899 from x=1532.5900, y=-0.0899 to make the flames brighter at the base.
The fire intensity looks good but now there is a purple tone in the fire root.
To lower the purple tone, change the blue flag to a lighter blue color. Select the flag, then right-click it and choose Change Selection Color.
Here, rgb (0.549, 0.675, 1) is used.
Although the default value of Step% works just fine, let’s lower it a bit to 50%. The lower step helps to capture the details which are smaller than a voxel, otherwise these details are either skipped or render very noisy. However, decreasing the step makes the render slower. In this case the time difference is very small, but gives you a better result. If you prefer a faster render, increase the Step% but this may lead to a less detailed image. If you prefer a faster render, increase the Step% but this may lead to a less detailed image.
Render.
Final Result
The final image is rendered with Bucket image sampler and the following settings: Min subdivs set to 1, Max subdivs set to 24, Light cache is 2500, and Noise threshold - 0.01.
