N_RayReflect

This BlinkScript Gizmo allows you to perform single-bounce raytracing, only requiring a camera, normals AOV, and HDRI.

Specular surfaces, as well as diffuse, and even transmissive, are supported. These surface properties can be a single constant value, or driven by input images to create materials as seen in the above turntable.

Setup

Simply clone/download this repo and add the following line to your init.py: nuke.pluginAddPath("/path/to/normal_ray_reflect/src/python"), replacing "/path/to" with the actual path to the repository. The gizmo will be available as "N_RayReflect" the next time you launch Nuke. There is an example in the examples directory; simply insert a normal pass to get started.

Inputs

• hdri
  • The HDRI image that will be seen in reflections/lighting
• camera
  • The camera to shoot rays out of
• normals
  • The normals pass that will be used to reflect, refract, and diffuse the rays
• diffuse
  • The diffuse colour of the surface represented by the normals pass if the diffuse "Use Input" is checked
• specular
  • The specular colour of the surface represented by the normals pass if the specular "Use Input" is checked
• transmission
  • The transmission colour of the surface represented by the normals pass if the transmission "Use Input" is checked
• specRoughness
  • The specular roughness values of the surface represented by the normals pass if the specular roughness "Use Input" is checked
• transRoughness
  • The transmission roughness values of the surface represented by the normals pass if the transmission roughness "Use Input" is checked

Knobs

• Normals
  • The channels to use as the normals pass.
• Ray Samples
  • The number of samples to use per pixel.
• Incident Refractive Index
  • The refractive index of the incoming ray medium.
• Refracted Refractive Index
  • The refractive index of the outgoing ray medium.
• HDRI Offset Angle
  • Rotate the HDRI by this amount.
• Diffuse Colour
  • The diffuse colour of the surface if the diffuse "Use Input" knob is not checked
• Specular Colour
  • The specular colour of the surface if the specular "Use Input" knob is not checked
• Transmission Colour
  • The transmission colour of the surface if the transmission "Use Input" knob is not checked
• Specular Roughness
  • The specular roughness of the surface if the specular roughness "Use Input" knob is not checked
• Transmission Roughness
  • The transmission roughness of the surface if the transmission roughness "Use Input" knob is not checked
• Use Input
  • These knobs toggle between the use of the corresponding knobs as a surface property, or the corresponding input
    • If you use the knob, ("Use Input" false) the entire surface will have the same value, which can be good for testing
    • If you use the input, ("Use Input" true) the surface property can be specified in an image, and therefore each pixel can take a different value
• Enable Precomputed Irradiance
  • Use a precomputed irradiance for diffuse lighting. This will require only one sample rather than many in order to converge.
• Irradiance Blur Size
  • Blur the HDRI by this amount before using it to compute the irradiance. This can help reduce artifacts caused by small, bright, light sources without increasing the 'Irradiance Samples'.
• Irradiance Samples
  • The number of samples in the horizontal direction that will be used to compute the irradiance of a hemisphere of the HDRI. Half this many samples will be used in the vertical direction.
• Output Irradiance
  • Enable this to view the irradiance.

Limitations

• There are no secondary reflections for any material
  • The transmissive objects are treated as shells
    • They have no back wall so rays are not refracted or reflected off the back of the shape
    • If the rays are meant to enter and exit the object the final refracted direction, and therefore the final colour will not be physically accurate

References

• Examples courtesy of Riley Gray
• HDRI from Greg Zaal at https://polyhaven.com/a/ninomaru_teien