How to use volumetrics?
Corona Renderer is a physically-based renderer, and just like in the real world, volumetric effects are a property of the material that light passes through, and not a property of the light source itself. This means that volumetrics are created in Corona Renderer for Cinema 4D using materials, and no special settings are required in the light sources themselves.
There are two approaches you can take, either using a Global Volume material for where the volumetric effects should fill the whole scene environment, or applying a volume material to specific objects in the scene to control where volumetric effects should occur (for example, for low lying fog or mist, etc.)
This can be found in the Scene Environment tab of the Render Settings:
By checking this, and adding a CoronaVolume material to the slot, volumetric effects will be calculated throughout the scene. There are three effects to control when using volumetrics:
- Absorption controls how much light is absorbed by the medium the light is traveling through. The darker the absorption color, or the lower the absorption distance, then the more light will be absorbed. This can be thought of as "thicker fog" if you like.
- Scattering controls how light is scattered (bounced around from its original direction) by the medium the light is traveling through. A brighter color will result in more intense scattering, while higher Direction will cause light to scatter more along its original direction, the default will cause it to scatter in all directions evenly, and lower (negative) values will cause it to scatter back toward the light source.
- Emission controls a constant "glow" from the medium, irrespective of any light passing through that point in the medium.
Below are some examples based on the free Paris Apartment scene from Slashcube (the Resources page has the download link for this and other free scenes) that show how the parameters of the CoronaVolume material affect the results:
Image 1, Baseline
This will be used as our baseline, and then one parameter at a time will be adjusted from these settings to show the effect. The most important value to set for the initial setup is the Absorption Distance. The exact value you need to use for this will depend on the size and scale of your scene.
Image 2, Absorption Distance
Lowering the absorption distance makes the volumetric effect absorb light more quickly (that is, more light is absorbed even when a light ray travels a lower distance through the volume), resulting in a darker environment.
Image 3, Absorption Color
Using a brighter color for the absorption color means the volumetric effect absorbs less light, resulting in a brighter environment. A slight orange tint was also added to the absorption color.
Image 4, Scattering Directionality
Lowering the directionality of the scattering means light is scattered less along the direction of travel for the light, and more back toward the light. This gives a softer, less well defined look to the scattering.
Image 5, Disabling Single Bounce Only
Turning off "Single bounce only" allows light rays to be scattered (and absorbed) more than once. Depending on your scene, this can increase realism, and the trade-off is that it will give longer render times. In many cases the effect may not be particularly noticeable and "Single bounce only" can be used without any perceived loss of realism.
Image 6, Emission
Emission adds a constant glow to the volumetric material.
CoronaVolume Applied to Objects
This approach should be used when the entire scene is not filled with a volumetric material, for example if you have a low-lying mist or fog, or if you want volumetrics to appear for particular windows, light sources, etc. In the example below, a cube was created and placed low to the ground, with a CoronaVolume material applied to it (the Global volume parameter in the Render Settings is unchecked of course):
For stage spotlights, for example, using either a global material approach or specific objects with a Corona Volume material applied will work, again depending on whether every light in the scene should show volumetric effects or not. Examples of each are shown below, using Cinema 4D's native Spotlights:
Cones were created as geometry, with a Corona Volume material applied to each - no global material was used.
The same scene but with a global volumetric material used (and some Emission added) - the cones geometry was removed