Environment - Arnold for Houdini
Further Reading |
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See also Environment in the Arnold User Guide |
You can create these shaders in the SHOP. Environment includes atmosphere nodes and background nodes.
- Fog
- Atmosphere_volume
- Physical_sky
Background
Background nodes include the sky shader, but a flat could also be assigned here.
Adding An Environment to a Scene
To add some atmosphere or background to a scene, first, create a shader in the SHOP. Double click to enter the VEX Builder and Tab-type (Custom > Fog/Atmosphere Volume/Sky. Connect the output of the atmosphere nodes to the atmosphere parameter of the environment output node and the sky node to the background parameter.
atmosphere_volume & background -> OUT_environment inside an Arnold Shader Network
In the Main tab of a Render Output, connect the required shaders to the environment parameter.
Fog
This atmospheric shader node simulates the effect of light scattering, which causes more distant objects to appear lower in contrast, especially in outdoor environments.
Atmosphere Volume
This shader simulates light scattered by a thin, uniform atmosphere. It produces shafts of light and volumetric shadows cast from geometric objects. It works with point, spot, and area lights, but not with distant or skylights. This is a scene-wide volume shader (or an atmosphere shader in Arnold's terms).
Physical Sky
This shader implements a variation of the Hosek-Wilkie sky radiance model, including the direct solar radiance function. You can plug it into the environment, or to the color input of a Skydome light (which benefits from efficient importance sampling, sending more rays to bright areas around the sun), or add it directly as an environment shader.
To use a physical_sky for lighting, first, create a skydome_light (Tab > Arnold > Arnold Light. Change Light Type to skydome . Change Color Type to Shader. This will add the Color Shader parameter showing the location of a vopnet that is contained inside the light node for convenience.
A physical_sky shader can be added inside this vopnet and connected to the color parameter of the Light Output.
If the physical_sky is also required to be visible to the camera, specular, or transmission rays then an Environment Output can be created in the same vopnet and the physical_sky connected to the background input.
This shader can then be linked to the Environment parameter of the Arnold ROP.
Alternatively, a vopnet could be created in the SHOP and a Fetch node used to grab the physical_sky
For convenience, a material has been created at the shop level which contains both a Light Output and Environment Output.