--- ray/doc/ray.html 2004/10/21 16:16:14 1.4 +++ ray/doc/ray.html 2023/11/15 18:28:10 1.33 @@ -1,7 +1,8 @@ + -The RADIANCE 3.6 Synthetic Imaging System +The RADIANCE 6.0 Synthetic Imaging System @@ -9,7 +10,7 @@ The RADIANCE 3.6 Synthetic Imaging System

-The RADIANCE 3.6 Synthetic Imaging System +The RADIANCE 6.0 Synthetic Imaging System

@@ -82,7 +83,7 @@ The diagram in Figure 1 shows the flow between program (ovals). The central program is rpict, which produces a picture from a scene description. -Rview is a variation of rpict that computes and displays images +Rvu is a variation of rpict that computes and displays images interactively, and rtrace computes single ray values. Other programs (not shown) connect many of these elements together, such as the executive programs @@ -564,7 +565,7 @@ A material defines the way light interacts with a sur

- Mirror is used for planar surfaces that produce secondary source reflections. + Mirror is used for planar surfaces that produce virtual source reflections. This material should be used sparingly, as it may cause the light source calculation to blow up if it is applied to many small surfaces. This material is only supported for flat surfaces such as polygons and rings. The arguments are simply the RGB reflectance values, which should be between 0 and 1. @@ -587,12 +588,12 @@ This is only appropriate if the surface hides other (m
- The prism1 material is for general light redirection from prismatic glazings, generating secondary light sources. + The prism1 material is for general light redirection from prismatic glazings, generating virtual light sources. It can only be used to modify a planar surface (i.e., a polygon or disk) and should not result in either light concentration or scattering. The new direction of the ray can be on either side of the material, - and the definitions must have the correct bidirectional properties to work properly with secondary light sources. + and the definitions must have the correct bidirectional properties to work properly with virtual light sources. The arguments give the coefficient for the redirected light and its direction. 
@@ -659,7 +660,7 @@ a perfectly scattering medium (no absorption).
 The scattering eccentricity parameter will likewise override the global
 setting if it is present.
 Scattering eccentricity indicates how much scattered light favors the
-forward direction, as fit by the Heyney-Greenstein function:
+forward direction, as fit by the Henyey-Greenstein function:
 
 
 	P(theta) = (1 - g*g) / (1 + g*g - 2*g*cos(theta))^1.5
@@ -797,7 +798,8 @@ unless the line integrals consider enclosed geometry.
 
 

 	Trans2 is the anisotropic version of trans.  
-	The string arguments  are  the same as for plastic2, and the real arguments are the same as  for  trans  but  with  an  additional roughness value.
+	The string arguments  are  the same as for plastic2,
+	and the real arguments are the same as  for  trans  but  with  an  additional roughness value.
 
 
         mod trans2 id
@@ -809,6 +811,29 @@ unless the line integrals consider enclosed geometry.
 

 
 

+	
+	Ashik2
+	
+
+

+	Ashik2 is the anisotropic reflectance model by Ashikhmin & Shirley.
+	The string arguments are the same as for plastic2, but the real
+	arguments have additional flexibility to specify the specular color.
+	Also, rather than roughness, specular power is used, which has no
+	physical meaning other than larger numbers are equivalent to a smoother
+	surface.
+	Unlike other material types, total reflectance is the sum of
+	diffuse and specular colors, and should be adjusted accordingly.
+
+	mod ashik2 id
+	4+ ux uy uz funcfile transform
+	0
+	8 dred dgrn dblu sred sgrn sblu u-power v-power
+

+
+

+
+

 	
 	Dielectric
 	
@@ -1053,6 +1078,116 @@ unless the line integrals consider enclosed geometry.
 

 
 

+	
+	BSDF
+	
+
+

+	The BSDF material type loads an XML (eXtensible Markup Language)
+	file describing a bidirectional scattering distribution function.
+	Real arguments to this material may define additional
+	diffuse components that augment the BSDF data.
+	String arguments are used to define thickness for proxied
+	surfaces and the "up" orientation for the material.
+
+
+	mod BSDF id
+	6+ thick BSDFfile ux uy uz funcfile transform
+	0
+	0|3|6|9
+		rfdif gfdif bfdif
+		rbdif gbdif bbdif
+		rtdif gtdif btdif
+

+
+

+	The first string argument is a "thickness" parameter that may be used
+	to hide detail geometry being proxied by an aggregate BSDF material.
+	If a view or shadow ray hits a BSDF proxy with non-zero thickness,
+	it will pass directly through as if the surface were not there.
+	Similar to the illum type, this permits direct viewing and
+	shadow testing of complex geometry.
+	The BSDF is used when a scattered (indirect) ray hits the surface,
+	and any transmitted sample rays will be offset by the thickness amount
+	to avoid the hidden geometry and gather samples from the other side.
+	In this manner, BSDF surfaces can improve the results for indirect
+	scattering from complex systems without sacrificing appearance or
+	shadow accuracy.
+	If the BSDF has transmission and back-side reflection data,
+	a parallel BSDF surface may be
+	placed slightly less than the given thickness away from the front surface
+	to enclose the complex geometry on both sides.
+	The sign of the thickness is important, as it indicates
+	whether the proxied geometry is behind the BSDF
+	surface (when thickness is positive) or in front (when
+	thickness is negative).
+

+	The second string argument is the name of the BSDF file,
+	which is found in the usual auxiliary locations.  The
+	following three string parameters name variables for an
+	"up" vector, which together with the surface
+	normal, define the local coordinate system that orients the
+	BSDF.  These variables, along with the thickness, are defined
+	in a function file given as the next string argument.  An
+	optional transform is used to scale the thickness and
+	reorient the up vector.
+

+	If no real arguments are given, the BSDF is used by itself
+	to determine reflection and transmission.  If there are at
+	least 3 real arguments, the first triplet is an additional
+	diffuse reflectance for the front side.  At least 6 real
+	arguments adds diffuse reflectance to the rear side of the
+	surface.  If there are 9 real arguments, the final triplet
+	will be taken as an additional diffuse transmittance.  All
+	diffuse components as well as the non-diffuse transmission
+	are modified by patterns applied to this material.  The
+	non-diffuse reflection from either side are unaffected.
+	Textures perturb the effective surface normal in the usual
+	way.
+

+	The surface normal of this type is not altered to face the
+	incoming ray, so the front and back BSDF reflections may
+	differ.  (Transmission is identical front-to-back by physical
+	law.) If back visibility is turned off during rendering and
+	there is no transmission or back-side reflection, only then
+	the surface will be invisible from behind.  Unlike other
+	data-driven material types, the BSDF type is fully supported
+	and all parts of the distribution are properly sampled.
+

+
+

+	
+	aBSDF
+	
+
+

+	The aBSDF material is identical to the BSDF type with two
+	important differences.  First, proxy geometry is not
+	supported, so there is no thickness parameter.  Second, an
+	aBSDF is assumed to have some specular through component
+	(the ’a’ stands for "aperture"),
+	which is treated specially during the direct calculation
+	and when viewing the material.  Based on the BSDF data, the
+	coefficient of specular transmission is determined and used
+	for modifying unscattered shadow and view rays.
+
+
+	mod aBSDF id
+	5+ BSDFfile ux uy uz funcfile transform
+	0
+	0|3|6|9
+	     rfdif gfdif bfdif
+	     rbdif gbdif bbdif
+	     rtdif gtdif btdif
+

+
+

+	If a material has no specular transmitted component, it is
+	much better to use the BSDF type with a zero thickness
+	than to use aBSDF.
+

+
+

 	
 	Antimatter
 	
@@ -1326,6 +1461,100 @@ or:
 	A section of text meant to  depict  a  picture, perhaps using a special purpose font such as hexbit4x1.fnt, calls for uniform  spacing.   
 	Reasonable  magnitudes  for  proportional  spacing are between 0.1 (for tightly spaced characters) and 0.3 (for wide spacing).
 
+

+
+

+	
+	Spectrum
+	
+
+

+	The spectrum primitive is the most basic type for introducing spectral
+	color to a material.
+	Since materials only provide RGB parameters, spectral patterns
+	are the only way to superimpose wavelength-dependent behavior.
+
+
+        mod spectrum id
+	0
+	0
+	5+ nmA nmB s1 s2 .. sN
+

+
+

+	The first two real arguments indicate the limits of the covered
+	spectral range in nanometers.
+	Subsequent real values correspond to multipliers in each wavelength band,
+	where the first band goes from nmA to nmA+(nmB-nmA)/N, and N is the
+	number of bands (i.e., the number of real arguments minus 2).
+	The nmA wavelength may be greater or less than the nmB wavelength,
+	but they may not be equal, and their ordering must correspond to
+	the ordering of the spectral values.
+	A minimum of 3 values must be given, which would act
+	more or less the same as a constant RGB multiplier.
+	As with RGB values, spectral quantities normally range between 0
+	and 1 at each wavelength, or average to 1.0 against a standard
+	sensitivity functions such as V(lambda).
+	The best results obtain when the spectral range and number
+	of samples match rendering options, though resampling will handle
+	any differences, zero-filling wavelenths outside the nmA to nmB
+	range.
+	A warning will be issued if the given wavelength range does not
+	adequately cover the visible spectrum.
+
+

+
+

+	
+	Specfile
+	
+
+

+	The specfile primitive is equivalent to the spectrum type, but
+	the wavelength range and values are contained in a 1-dimensional
+	data file.
+	This may be a more convenient way to specify a spectral color,
+	especially one corresponding to a standard illuminant such as D65
+	or a library of measured spectra.
+
+
+        mod specfile id
+	1 datafile
+	0
+	0
+

+
+

+	As with the spectrum type, rendering wavelengths outside the defined
+	range will be zero-filled.
+	Unlike the spectrum type, the file may contain non-uniform samples.
+
+

+
+

+	
+	Specfunc
+	
+
+

+	The specfunc primitive offers dynamic control over a spectral
+	pattern, similar to the colorfunc type.
+
+
+        mod specfunc id
+	2+ sval funcfile transform
+	0
+	2+ nmA nmB A3 ..
+

+
+

+	Like the spectrum primitive, the wavelength range is specified
+	in the first two real arguments, and additional real values are
+	accessible to the sval function.
+	This function is fed a wavelenth sample
+	between nmA and nmB as its only argument,
+	and it returns the corresponding spectral intensity.
+
 
 
 

@@ -1336,6 +1565,7 @@ or:
 
 
 A mixture is a blend of one or more materials or textures and patterns.
+Blended materials should not be light source types or virtual source types.
 The basic types are given below.
 
 

@@ -1365,8 +1595,6 @@ A mixfunc mixes  two  modifiers  procedurally.   It  i
 	which serves as a form of opacity control when used with a material.)
 	Vname is the coefficient defined in funcfile that determines  the  influence  of  foreground.   
 	The background coefficient is always (1-vname).  
-	Since the references are not resolved until run-time,  the  last  definitions  of  the modifier id's will be used.  
-	This can result in modifier loops, which are detected by the renderer.
 
 

 
@@ -1410,7 +1638,6 @@ A mixfunc mixes  two  modifiers  procedurally.   It  i
 	arguments, the red, green and blue values
 	corresponding to the pixel at (u,v).
 
-
 

 
 

@@ -1528,10 +1755,8 @@ If no file is needed by a given primitive because all
 the  required  variables  are global,  
 a  period  (`.')  can be given in place of the file name.  
 It is also possible to give an expression instead
-of a  straight  variable  name  in  a scene file, 
-although such expressions should be kept
-simple if possible.
-Also, functions (requiring parameters) must be given
+of a  straight  variable  name  in  a scene file.
+Functions (requiring parameters) must be given
 as names and not as expressions.
 
 

@@ -1678,7 +1903,7 @@ The details of this process  are  not  important, but 
 directs the use of a scene description.