Scene Description Changes from pbrt-v3 to pbrt-v4

This list is currently based off the changes made up to this commit- https://github.com/mmp/pbrt-v4/tree/cdccb7

Table of Contents

• Preamble
• Base Scene Description
• Camera
• Film
• Filter
• Sampler
• Integrator
• Light
• Material
• Texture
• Shape
• Medium

Preamble

This is not meant to be the official document representing the changes between pbrt-v3 and pbrt-v4, I'll leave that to Matt's much more capable hands. These are my notes during the process of updating an exporter from v3 to v4. I am making these public to aid others in the transition until a formal page is created by Matt. The changes listed are deduced from reading through the source code of https://github.com/mmp/pbrt-v4. As pbrt-v4 is still an early release and changing rapidly expect these notes to be out of sync at times. When in doubt, trust the code! :)

Updating an exporter while the interface is still undergoing changes?

Yup, I'm an idiot. But its exciting to follow the developments and try out the changes!

Legend

A few emoji are used to call attention for the reasons listed below-

Icon	Reasoning
❗	Significant change to scene description structure

Base Scene Description Changes

• ❗WorldEnd has been removed
• ❗TransformBegin and TransformEnd are deprecated, use AttributeBegin and AttributeEnd instead.
• New Import statement, similar to the Include but does not maintain graphics state (but does maintain defined objects).
• New ColorSpace "name" graphics state Attribute(?)
  Sets the ColorSpace to be "name" which defines the color space of spectrum parameters. Accepts the following builtin names -
  • srgb (default)
  • dci-p3
  • rec2020
  • aces2065-1
• New Attribute "target" "parm" [ value ] for setting parameter "overrides" for various targets which include -
  • shape
  • light
  • material
  • medium
  • texture
• New Option "name" "value" call added
  This sets some global options including
  • bool disablepixeljitter (false)
  • bool disablewavelengthjitter (false)
  • bool disabletexturefiltering (false)
  • float displacementedgescale (1.0)
  • string rendercoordsys valid values are:
    • camera
    • cameraworld (default)
    • world
  • string msereferenceimage ("")
  • string msereferenceout ("")
  • integer seed (0)
  • bool forcediffuse (false)
  • bool pixelstats (false)
  • bool wavefront (false)
• Type Changes
  • ❗ bool types are no longer quoted
    • pbrt-v3 "bool parm" ["true"]
    • pbrt-v4 "bool parm" [true]
  • ❗ spectrum type changes
    • spectrum blackbody parameters should no longer specify an intensity value
      • pbrt-v3 "blackbody parm" [6500 0.5]
      • pbrt-v4 "blackbody parm" [6500]
    • spectrum xyz parameters are no longer supporter
      • pbrt-v3 "xyz parm" [ 0.2 0.5 0.8 ]
      • pbrt-v4 not supported

Camera Changes

EnvironmentCamera is now SphericalCamera

• Declaration is now "spherical" (was "environment")
• New string mapping parameter with possible values of
  • equalarea (default)
  • equirectangle

PerspectiveCamera

• Remove float halffov parameter (just use "fov" parameter)

RealisticCamera

• New string aperture parameter (defaults to "")
  This parameter supports a image file path or one of the following built-ins
  • gaussian
  • square
  • pentagon
  • star

Film Changes

General Film Changes

• Default film is "rgb"
• Currently both RGBFilm and GBufferFilm have the same parameters.
• New Sensor Parameters:
  • float iso defaults to 100
  • float whitebalance defaults to 0
    If your whitebalance is 0, and your sensor is something other than cie1931, pbrt will automatically default the sensor to 6500
  • string sensor defaults to "cie1931"
    The sensor parameter accepts any of the following camera sensors.

Parm Value	Common Name
cie1931	CIE 1931
canon_eos_100d	Canon EOS 100D
canon_eos_1dx_mkii	Canon EOS 1D X Mark II
canon_eos_200d	Canon EOS-200D
canon_eos_200d_mkii	Canon EOS 200D Mark II
canon_eos_5d	Canon EOS 5D
canon_eos_5d_mkii	Canon EOS 5D Mark II
canon_eos_5d_mkiii	Canon EOS 5D Mark III
canon_eos_5d_mkiv	Canon EOS 5D Mark IV
canon_eos_5ds	Canon EOS 5DS
canon_eos_m	Canon EOS M
hasselblad_l1d_20c	Hasselblad L1D-20C
nikon_d810	Nikon D810
nikon_d850	Nikon D850
sony_ilce_6400	Sony A6400
sony_ilce_7m3	Sony A7 Mark III
sony_ilce_7rm3	Sony A7R Mark III
sony_ilce_9	Sony A9

ImageFilm is now RGBFilm

• Declaration is now "rgb" (was "image")
• xresolution and yresolution defaults have changed to (1280x720) respectively.
• integer[4] pixelbounds parameter added. If crop region is specificed it will override this.
  (this previously lived on certain integrators)
• float maxsampleluminance changed to float maxcomponentvalue
• New bool savefp16 parameter for saving half images. (default true)

New GBufferFilm

• Declaration is "gbuffer"
• Parameters are the same as RGBFilm with the additional -
  • string coordinatesystem defaults to "camera"
    Possible values include:
    • "camera"
    • "world"

New SpectralFilm

• Declaration is "spectral"
• Parameters are the same as RGBFilm with the additional -
  • integer buckets defaults to 16
  • float lambdamin defaults to 360
  • float lambdamax defaults to 830

Filter Changes

All Filters

• Rename float xwidth to float xradius
• Rename float ywidth to float yradius

Gaussian Filter

• float xradius and float yradius defaults are now 1.5
• float alpha is now float sigma default is 0.5

Sampler Changes

The default sampler is "zsobol"

• All samplers have a int seed parameter that defaults to a global Option "seed" value

Remove MaxMinDist Sampler

Renamed Random Sampler to Independent Sampler

• Declared with "independent"

New PMJ02BN Sampler

• Declared with "pmj02bn"
• Parameters:
  • integer pixelsamples parameter (defaults to 16)

New ZSobolSampler

• Declared with "zsobol"
• This has the same parameters as the Sobol Sampler

02Sequence Sampler has become the more aptly named PaddedSobol Sampler

• Declared with "paddedsobol"
• This has the same parameters as the Sobol Sampler

Sobol Sampler

• New string randomization parameter with the following options
  • none
  • owen
  • fastowen (default)
  • permutedigits

Stratified Sampler

• Remove integer dimensions parameter

Halton Sampler

• Remove bool samplepixelcenter parameter
• New string randomization parameter with the following options
  • none
  • owen
  • permutedigits (default)

Integrator Changes

General

• integer[4] pixelbounds that existed on the various Integrators has been removed and now live on Film
• Default integrator is now VolumePath

Remove Whitted Integrator

Remove DirectLighting Integrator

New LightPath Integrator

• Declared with "lightpath"
• Parameters:
  • integer maxdepth defaults to 5

New RandomWalk Integrator

• Declared with "randomwalk"
• Parameters:
  • integer maxdepth defaults to 5

New Function Integrator

• Declared with "function"
• Parameters:
  • string function The following options are supported
    • step (default)
    • diagonal
    • disk
    • checkerboard
    • rotatedcheckerboard
    • gaussian
  • bool skipbad (true)
  • string filename defaults to Options->imageFile if supplied otherwise {function}-mse.txt
  • string imagefilename ("")

New SimplePath Integrator

• Declared with "simplepath"
• Parameters:
  • integer maxdepth defaults to 5
  • bool samplelights defaults to true
  • bool samplebsdf defaults to true

New SimpleVolPath Integrator

• Declared with "simplevolapath"
• Parameters:
  • integer maxdepth defaults to 5

Rename AO Integrator

• Type name is now "ambientocclusion", previously it was "ao"
• Remove integer maxsamples parameter
• New float maxdistance parameter, defaults to Inf

BDPT Integrator

• Replace string lightsamplestrategy with string lightsampler
  The following options are supported
  • uniform
  • ❗ power (default)
    BDPT's lightsampler default is different from Path/VolPath
  • bvh
  • exhaustive (new)
• New bool regularize parameter, defaults to false

MLT Integrator

• New bool regularize parameter, defaults to false

Path Integrator

• Replace string lightsamplestrategy with string lightsampler
  The following options are supported
  • uniform
  • power
  • bvh (default)
  • exhaustive (new)
• New bool regularize parameter, defaults to false
• Remove float rrthreshold parameter

SPPM Integrator

• New integer seed parameter, defaults to 6502
  (This does not lookup the seed value stored in Options)
• Remove integer iterations parameter

VolPath Integrator

• Replace string lightsamplestrategy with string lightsampler
  The following options are supported
  • uniform
  • power
  • bvh (default)
  • exhaustive (new)
• New bool regularize parameter, defaults to false
• Remove float rrthreshold parameter

Light Changes

All Lights

• spectrum scale is now float scale
• New float power parameter defaults to -1

Goniometric Light

• string mapname is now string filename

Infinite Light

• Remove integer samples parameter
• string mapname is now string filename
• New float illuminance parameter, defaults to -1
• New point[4] portal parameter
• spectrum L and string filename are mutually exclusive and should not be declared together. If portal and L are used, L is converted to an RGB texture.

Projection Light

• string mapname is now string filename
• Remove spectrum I parameter
  Spectrum values come only from the supplied image
• New float power parameter, defaults to -1
• float fov default has changed from 45 to 90

Diffuse AreaLight

• Remove integer samples parameter
• New "string filename" parameter, defaults to ""
• New float power parameter, defaults to -1
• spectrum L and string filename are mutually exclusive and should not be declared together.
• Alpha textures act on emission similar to visiblity. A special case when alpha is a constant 0 will result in an emissive invisible light source.

Distant Light

• New float illuminance parameter, defaults to -1

Material Changes

General Changes

• float texture bumpmap has been renamed to float texture displacement
• string normalmap has been added, defaults to ""

Following Materials Have Been Removed

• Uber
• Translucent
• Substrate
• Plastic
• Mirror
• Metal
• Matte
• KdSubsurface
• Glass
• Fourier
• Disney

None Material renamed Interface Material

• Declared with "interface", lights with an interface material are ignored.

CoatedConductor Material

Type name: "coatedconductor"

Parameters:

• float texture displacement defaults to null
• spectrum interface.eta defaults to 1.5
• float texture thickness defaults to 0.01
• float texture interface.roughness defaults to 0
• float texture interface.uroughness defaults to interface.roughness
• float texture interface.vroughness defaults to interface.roughness
• spectrum texture conductor.eta defaults to "metal-Cu-eta"
• spectrum texture conductor.k defaults to "metal-Cu-k"
• spectrum texture reflectance defaults to null, not to be used with conductor.eta and conductor.k
• float texture conductor.roughness defaults to 0
• float texture conductor.uroughness defaults to conductor.roughness
• float texture conductor.vroughness defaults to conductor.roughness
• bool remaproughness defaults to true
• integer maxdepth defaults to 10
• integer nsamples defaults to 1
• float texture g defaults to 0
• spectrum texture albedo defaults to 0

CoatedDiffuse Material

Type name: "coateddiffuse"

Parameters:

• float texture displacement defaultsto null
• spectrum texture reflectance defaults to 0.5
• spectrum eta default 1.5
• float texture thickness default 0.01
• float texture roughness defaults to 0
• float texture uroughness defaults to roughness
• float texture vroughness defaults to roughness
• bool remaproughness defaults to true
• integer maxdepth defaults to 10
• integer nsamples defaults to 1
• float texture g defaults to 0
• spectrum texture albedo defaults to 0

Conductor Material

Type name: "conductor"

Parameters:

• float texture displacement defaults to null
• spectrum texture eta defaults to "metal-Cu-eta"
• spectrum texture k defaults to "metal-Cu-k"
• spectrum texture reflectance defaults to null, not to be used with eta and k
• float texture roughness defaults to 0
• float texture uroughness defaults to roughness
• float texture vroughness defaults to roughness
• bool remaproughness defaults to true

Diffuse Material

Type name: "diffuse"

Parameters:

• float texture displacement defaults to null
• spectrum texture reflectance defaults to 0.5

DiffuseTransmission Material

Type name: "diffusetransmission"

Parameters:

• float texture displacement defaults to null
• spectrum texture reflectance defaults to 0.25
• spectrum texture transmittance defaults to 0.25
• float scale defaults to 1

Measured Material

Type name: "measured"

Parameters:

• float texture displacement defaults to null
• string filename defaults to ""

ThinDielectric Material

Type name: "thindielectric"

Parameters:

• float texture displacement defaults to null
• spectrum eta defaults to 1.5

Dielectric Material

Type name: "dielectric"

Parameters:

• float texture displacement defaults to null
• spectrum eta defaults to 1.5
• float texture roughness defaults to 0
• float texture uroughness defaults to roughness
• float texture vroughness defaults to roughness
• bool remaproughness defaults to true

Subsurface Material

• Remove spectrum Kr parameter
• Remove spectrum Kt parameter
• New spectrum texture reflectance defaults to 1
• New spectrum texture mfp defaults to 1
• New float g defaults to 0
• New float texture roughness defaults to 0

Mix Material

• Change spectrum texture amount to float texture amount
• Remove string namedmaterial1 and string namedmaterial2
• Add string[2] materials

Hair Material

• Change spectrum texture color to spectrum texture reflectance (color still works if reflectance isn't specified)

Texture Changes

Remove UVTexture

New DirectionMix Texture

• Supports both float and spectrum
• Parameters are
  • float|spectrum texture tex1 defaults to 0.0
  • float|specturm texture tex2 defaults to 1.0
  • vector3 dir defaults to (0.0, 1.0, 0.0)

Fbm Texture

• Output is now only float, in pbrt-v3 it was float and spectrum.

ImageMap Texture

• New float scale parmeter, defaults to 1
• New "octahedralsphere" mode for string wrap
• Remove bool trilinear parameter
• New string filter parameter, options include
  • point
  • bilinear (default)
  • trilinear
  • ewa
• Remove bool gamma parameter
• New bool invert parameter, defaults to false
• New string encoding parameter, this accepts either a builtin name or a "gamma value".
  One of the following options can be specified. (The default is based on the file extension of the texture.)
  • linear
  • sRGB
  • gamma float_value

Marble Texture

• Output is now only spectrum, in pbrt-v3 it was float and spectrum

Scale Texture

• texture tex1 is now just texture tex
• texture tex2 has been replaced with float scale, defaults to 1

Windy Texture

• Output is now only float, in pbrt-v3 it was float and spectrum.

Wrinkled Texture

• Output is now only float, in pbrt-v3 it was float and spectrum.

Ptex Texture

• New float scale parameter, defaults to 1

Shape Changes

General

• All shapes now support an float texture alpha parameter.
• ❗ Shapes no longer support overriding of a Material's parameters as described here https://www.pbrt.org/fileformat-v3.html#materials

Shape Removals

• Cone
• HeightField
• NURBS
• Hyperboloid
• Paraboloid

New Bilinear Patch Mesh

• Declared with "bilinearmesh"
• Parameters:
  • point3[] P
  • integer[] indices
  • point2[] uv optional
  • normal3[] N optional
  • integer[] faceIndices optional
  • string emissionfilename optional

Triangle Shape

• Remove texture shadowalpha parameter
• ❗Change uv parameter from float[] uv to point2[] uv

Ply Shape

• Remove texture shadowalpha parameter
• Add float texture displacement parameter, defaults to null (deactivated)
• Add float edgelength parameter, defaults to 1.0

Medium Changes

Homogeneous Medium

• New spectrum Le parameter, defaults to 0
• string preset default ("") Only exists on Homogeneous Medium
• The list of presets scattering properties has not changed since pbrt-v3*

New Uniform Medium

This was previously the Heterogeneous Medium in pbrt-v3

• Declare with "uniformgrid"
• Parameters:
  • General Medium parameters described above
  • float[] density
  • float[] temperature
  • float[] Lescale
  • Only one combination of Le or temperature is allowed
  • spectrum sigma_a defaults to (1, 1, 1)
  • spectrum sigma_s defaults to (1, 1, 1)
  • spectrum Le defaults to 0
  • float scale defaults to 1.0
  • float g defaults to 0.0
  • integer nx defaults to 1
  • integer ny defaults to 1
  • integer nz defaults to 1
  • point3 p0 defaults to (0,0,0)
  • point3 p1 defaults to (1,1,1)

New RGBGrid Medium

• Declare with "rgbgrid"
• Parameters:
  • rgb[] sigma_a
  • rgb[] sigma_s
  • rgb[] Le
  • Can specify sigma_a and/or sigma_s. But if Le is used then sigma_a is required.
  • float LeScale defaults to 0
  • float scale defaults to 1.0
  • float g defaults to 0.0
  • integer nx defaults to 1
  • integer ny defaults to 1
  • integer nz defaults to 1
  • point3 p0 defaults to (0,0,0)
  • point3 p1 defaults to (1,1,1)

New Cloud Medium

• Declare with "cloud"
• Parameters:
  • float density defaults to 1
  • float wispiness defaults to 1
  • float frequency defauts to 5
  • spectrum sigma_a defaults to (1, 1, 1)
  • spectrum sigma_s defaults to (1, 1, 1)
  • spectrum Le defaults to 0
  • float g defaults to 0.0
  • point3 p0 defaults to (0,0,0)
  • point3 p1 defaults to (1,1,1)

New NanoVDB Medium

• Declare with "nanovdb"
  Looks for fields within the VDB of the name "density" and "temperature"
• Parameters:
  • General Medium parameters described above
  • string filename defaults to ""
  • float LeScale defaults to 1.0
  • float temperaturecutoff defaults to 0.0
  • float temperaturescale defaults to 1.0
  • spectrum sigma_a defaults to (1, 1, 1)
  • spectrum sigma_s defaults to (1, 1, 1)
  • float scale defaults to 1.0