--- ray/doc/ray.html 2006/05/10 19:50:30 1.6 +++ ray/doc/ray.html 2023/12/12 20:25:22 1.37 @@ -1,7 +1,8 @@ + -The RADIANCE 3.7 Synthetic Imaging System +The RADIANCE 6.0 Synthetic Imaging System @@ -9,7 +10,7 @@ The RADIANCE 3.7 Synthetic Imaging System

-The RADIANCE 3.7 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 @@ -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 +1461,98 @@ 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 extrema of the
+	spectral range in nanometers.
+	Subsequent real values correspond to multipliers at each wavelength.
+	The nmA wavelength may be greater or less than nmB,
+	but they may not be equal, and their ordering matches
+	the order 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+ sfunc 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
+	set in the evaluation context.
+	This function is fed a wavelenth sample
+	between nmA and nmB as its only argument,
+	and it returns the corresponding spectral intensity.
+
 
 
 

@@ -1336,6 +1563,7 @@ 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 +1593,6 @@ 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 +1636,6 @@ A mixfunc mixes  two  modifiers  procedurally.   It  i
 	arguments, the red, green and blue values
 	corresponding to the pixel at (u,v).
 
-
 

 
 

@@ -1528,10 +1753,8 @@ 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 +1901,7 @@ The details of this process  are  not  important, but 
 directs the use of a scene description.