man/man1/rcontrib.1

.\" RCSid "$Id: rcontrib.1,v 1.26 2025/04/23 15:09:03 greg Exp $"
.TH RCONTRIB 1 5/25/05 RADIANCE
.SH NAME
rcontrib - compute contribution coefficients in a RADIANCE scene
.SH SYNOPSIS
.B rcontrib
[
.B "\-n nprocs"
][
.B \-V
][
.B "\-t secs"
][
.B "\-c count"
][
.B \-fo
|
.B \-r
][
.B "\-o ospec"
][
.B "\-p p1=V1,p2=V2"
][
.B "\-b binv"
][
.B "\-bn nbins"
]
{
.B "\-m mod | \-M file"
}
..
[
.B $EVAR
]
[
.B @file
]
[
rtrace options
]
.B octree
.br
.B "rcontrib [ options ] \-defaults"
.br
.B "rcontrib \-features [feat1 ..]"
.SH DESCRIPTION
.I Rcontrib
computes ray coefficients
for objects whose modifiers are named in one or more
.I \-m
settings.
These modifiers are usually materials associated with
light sources or sky domes, and must directly modify some geometric
primitives to be considered in the output.
A modifier list may also be read from a file using the
.I \-M
option.
The RAYPATH environment variable determines directories to search for
this file.
(No search takes place if a file name begins with a '.', '/' or '~'
character.)\0
.PP
If the
.I \-n
option is specified with a value greater than 1, multiple
processes will be used to accelerate computation on a shared
memory machine.
Note that there is no benefit to using more processes
than there are local CPUs available to do the work, and the
.I rcontrib
process itself may use a considerable amount of CPU time.
.PP
By setting the boolean
.I \-V
option, you may instruct
.I rcontrib
to report the contribution from each material rather than the ray
coefficient.
This is particularly useful for light sources with directional output
distributions, whose value would otherwise be lost in the shuffle.
With the default
.I -V-
setting, the output of rcontrib is a coefficient that must be multiplied
by the radiance of each material to arrive at a final contribution.
This is more convenient for computing daylight coefficeints, or cases
where the actual radiance is not desired.
Use the
.I -V+
setting when you wish to simply sum together contributions
(with possible adjustment factors) to obtain a final radiance value.
Combined with the
.I \-i
or
.I \-I
option, irradiance contributions are reported by
.I \-V+
rather than radiance, and 
.I \-V-
coefficients contain an additonal factor of PI.
.PP
The
.I \-c
option tells
.I rcontrib
how many rays to accumulate for each record.
The default value is one, meaning a full record will be produced for
each input ray.
For values greater than one, contributions will be averaged together
over the given number of input rays.
If set to zero, only a single record will be produced at the very
end, corresponding to the sum of all rays given on the input
(rather than the average).
This is equivalent to passing all the output records through a program like
.I total(1)
to sum RGB values together, but is much more efficient.
Using this option, it is possible to reverse sampling, sending rays from
a parallel source such as the sun to a diffuse surface, for example.
Note that output flushing via zero-direction rays is disabled with
.I \-c
set to zero.
.PP
Output flushing at fixed intervals may be enabled with the
.I \-x
option, which specifies the number of records
(-c accumulations) before each flush.
If the
.I \-y
option is also set, then periodic flushing is disabled and the
output size for an RGB image is the taken from the x and y dimensions.
In lieu of periodic flushing, a flush may be forced as mentioned above
by sending a sample with a zero direction vector, although you
must still send a full record of rays before output occurs.
.PP
If progress reports are desired, the
.I \-t
option specifies a time interval in seconds for reports sent to
standard error.
This requires that the number of input samples is known, meaning a
.I \-y
parameter has been specified.
.PP
The output of
.I rcontrib
has many potential uses.
Source contributions can be used as components in linear combination to
reproduce any desired variation, e.g., simulating lighting controls or
changing sky conditions via daylight coefficients.
More generally,
.I rcontrib
can be used to compute arbitrary input-output relationships in optical
systems, such as luminaires, light pipes, and shading devices.
.PP
.I Rcontrib
sends the accumulated rays tallies
to one or more destinations according to the given
.I \-o
specification.
If a destination begins with an exclamation mark ('!'), then
a pipe is opened to a command and data is sent to its standard input.
Otherwise, the destination is treated as a file.
An existing file of the same name will not be clobbered, unless the
.I \-fo
option is given.
If instead the
.I \-r
option is specified, data recovery is attempted on existing files.
(If 
.I "\-c 0"
is used together with the
.I \-r
option, existing files are read in and new ray evaluations are added
to the previous results, providing a convenient means for
progressive simulation.)\0
If an output specification contains a "%s" format, this will be
replaced by the modifier name.
The
.I \-b
option may be used to further define
a "bin number" within each object if finer resolution is needed, and
this will be applied to a "%d" format in the output file
specification if present. 
(The final integer will be offset incrementally
if the output is a RADIANCE picture and more than one modifier has
the same format specification.)\0
The actual bin number is computed at run time based on ray direction
and surface intersection, as described below.
The number of bins must be specified in advance with the
.I \-bn
option, and this is critical for output files containing multiple values
per record.
A variable or constant name may be given for this parameter if
it has been defined via a previous
.I \-f
or
.I \-e
option.
Since bin numbers start from zero, the bin count is always equal to
the last bin plus one.
The most recent
.I \-p,
.I \-b,
.I \-bn
and
.I \-o
options to the left of each
.I \-m
name are the ones used for that modifier.
Any
.I \-cs
option changing the number of spectral color
samples must appear before the first modifier.
The ordering of other options is unimportant, except for
.I \-x
and
.I \-y
if the
.I \-c
is zero, when they control the resolution string
produced in the corresponding output.
.PP
If a
.I \-b
expression is defined for a particular modifier,
the bin number will be evaluated at run time for each
ray contribution.
Specifically, each ray's world intersection point will be assigned to
the variables Px, Py, and Pz, and the normalized ray direction
will be assigned to Dx, Dy, and Dz.
These parameters may be combined with definitions given in
.I \-e
arguments and files read using the
.I \-f
option.
Additional parameter values that apply only to this modifier may be specified
with a
.I \-p
option, which contains a list of variable names and assigned values, separated
by commas, colons, or semicolons.
The computed bin value will be
rounded to the nearest whole number.
(Negative bin values will be silently ignored.)\0
For a single bin, you may specify
.I "\-b 0",
which is the default.
This mechanism allows the user to define precise regions or directions
they wish to accumulate, such as the Tregenza sky discretization,
which would be otherwise impossible to specify
as a set of RADIANCE primitives.
The rules and predefined functions available for these expressions are
described in the
.I rcalc(1)
man page.
Like the other rendering tools,
.I rcontrib
will search the 
.I RAYPATH
library directories for each file given in a
.I \-f
option.
However, a special evaluation context is set for the
.I \-f
and
.I \-e
definitions, so attach a back-quote ('`') to variable and function names
you wish these to apply at the global evaluation level and used by all
materials and modifiers during rendering.
.PP
If no
.I \-o
specification is given, results are written on the standard output in order
of modifier (as given on the command line) then bin number.
Concatenated data is also sent to a single destination (i.e., an initial
.I \-o
specification without formatting strings).
If a "%s" format appears but no "%d" in the
.I \-o
specification, then each modifier will have its own output file, with
multiple values per record in the case of a non-zero
.I \-b
definition.
If a "%d" format appears but no "%s", then each bin will get its own
output file, with modifiers output in order in each record.
For text output, each RGB coefficient triple is separated by a tab,
with a newline at the end of each ray record.
For binary output formats, there is no such delimiter to mark
the end of each record.
.PP
Input and output format defaults to plain text, where each ray's
origin and direction (6 real values) are given on input,
and one line is produced per output file per ray.
Alternative data representations may be specified by the
.I \-f[io]
option, which is described in the
.I rtrace
man page along with the associated
.I \-x
and
.I \-y
resolution settings.
In particular, the color ('c') output data representation
together with positive dimensions for
.I \-x
and
.I \-y
will produce an uncompressed RADIANCE picture,
suitable for manipulation with
.I pcomb(1)
and related tools.
.PP
Options may be given on the command line and/or read from the
environment and/or read from a file.
A command argument beginning with a dollar sign ('$') is immediately
replaced by the contents of the given environment variable.
A command argument beginning with an at sign ('@') is immediately
replaced by the contents of the given file.
.PP
.I Rcontrib
supports light source contributions from photon maps generated by
.I mkpmap(1)
with its
.I -apC
option. Enabling photon mapping is described in the
.I rtrace 
man page along with its relevant settings. In photon mapping mode,
.I rcontrib
only supports contributions from light sources, not arbitrary modifiers.
The
.I -b
option is supported along with its associated ray variables, as
discussed above. Ray coefficients are also supported via the
.I \-V-
option. Using fewer photons than there are light sources for the photon
density estimates results in omitted contributions, thus the bandwidth
is clamped accordingly and a warning is issued. 
.SH EXAMPLES
To compute the proportional contributions from sources modified
by "light1" vs. "light2" on a set of irradiance values:
.IP "" .2i
rcontrib \-I+ @render.opt \-o c_%s.dat \-m light1 \-m light2 scene.oct < test.dat
.PP
To generate a pair of images corresponding to these two lights'
contributions:
.IP "" .2i
vwrays \-ff \-x 1024 \-y 1024 \-vf best.vf |
rcontrib \-ffc `vwrays \-d \-x 1024 \-y 1024 \-vf best.vf`
@render.opt \-o c_%s.hdr \-m light1 \-m light2 scene.oct
.PP
These images may then be recombined using the desired outputs
of light1 and light2:
.IP "" .2i
pcomb \-c 100 90 75 c_light1.hdr \-c 50 55 57 c_light2.hdr > combined.hdr
.PP
To compute an array of irradiance contributions according to a Tregenza sky:
.IP "" .2i
rcontrib \-I+ \-f tregenza.cal \-b tbin \-bn Ntbins \-o sky.dat \-m skyglow
\-b 0 \-o ground.dat \-m groundglow @render.opt scene.oct < test.dat
.PP
To perform an annual simulation of 365 daily sun positions in photon mapping
mode:
.IP "" .2i
rcontrib \-I+ \-h \-V \-fo \-o c_%s.dat \-M lights \-ap contrib.pm 365
scene.oct < test.dat,
.SH ENVIRONMENT
RAYPATH         path to search for \-f and \-M files
.SH BUGS
We do not currently compute contributions or coefficients properly
in scenes with participating media.
A single warning will be issued if a scattering or absorbing medium
is detected.
.SH AUTHOR
Greg Ward
.SH "SEE ALSO"
cnt(1), dctimestep(1), genklemsamp(1), getinfo(1), mkpmap(1), pcomb(1), pfilt(1), 
pvsum(1), ra_rgbe(1), rcalc(1), rcomb(1), rfluxmtx(1), rmtxop(1), rpict(1),
rsensor(1), rtrace(1), rxfluxmtx(1), total(1), vwrays(1), ximage(1)

Revision:	1.27
Committed:	Thu Oct 23 23:34:59 2025 UTC (2 weeks, 1 day ago) by greg
Branch:	MAIN
CVS Tags:	HEAD
Changes since 1.26:	+2 -6 lines
Log Message:	docs: Added rxfluxmtx man page and updated others accordingly
#	Content
1	.\" RCSid "$Id: rcontrib.1,v 1.26 2025/04/23 15:09:03 greg Exp $"
2	.TH RCONTRIB 1 5/25/05 RADIANCE
3	.SH NAME
4	rcontrib - compute contribution coefficients in a RADIANCE scene
5	.SH SYNOPSIS
6	.B rcontrib
7	[
8	.B "\-n nprocs"
9	][
10	.B \-V
11	][
12	.B "\-t secs"
13	][
14	.B "\-c count"
15	][
16	.B \-fo
17	\|
18	.B \-r
19	][
20	.B "\-o ospec"
21	][
22	.B "\-p p1=V1,p2=V2"
23	][
24	.B "\-b binv"
25	][
26	.B "\-bn nbins"
27	]
28	{
29	.B "\-m mod \| \-M file"
30	}
31	..
32	[
33	.B $EVAR
34	]
35	[
36	.B @file
37	]
38	[
39	rtrace options
40	]
41	.B octree
42	.br
43	.B "rcontrib [ options ] \-defaults"
44	.br
45	.B "rcontrib \-features [feat1 ..]"
46	.SH DESCRIPTION
47	.I Rcontrib
48	computes ray coefficients
49	for objects whose modifiers are named in one or more
50	.I \-m
51	settings.
52	These modifiers are usually materials associated with
53	light sources or sky domes, and must directly modify some geometric
54	primitives to be considered in the output.
55	A modifier list may also be read from a file using the
56	.I \-M
57	option.
58	The RAYPATH environment variable determines directories to search for
59	this file.
60	(No search takes place if a file name begins with a '.', '/' or '~'
61	character.)\0
62	.PP
63	If the
64	.I \-n
65	option is specified with a value greater than 1, multiple
66	processes will be used to accelerate computation on a shared
67	memory machine.
68	Note that there is no benefit to using more processes
69	than there are local CPUs available to do the work, and the
70	.I rcontrib
71	process itself may use a considerable amount of CPU time.
72	.PP
73	By setting the boolean
74	.I \-V
75	option, you may instruct
76	.I rcontrib
77	to report the contribution from each material rather than the ray
78	coefficient.
79	This is particularly useful for light sources with directional output
80	distributions, whose value would otherwise be lost in the shuffle.
81	With the default
82	.I -V-
83	setting, the output of rcontrib is a coefficient that must be multiplied
84	by the radiance of each material to arrive at a final contribution.
85	This is more convenient for computing daylight coefficeints, or cases
86	where the actual radiance is not desired.
87	Use the
88	.I -V+
89	setting when you wish to simply sum together contributions
90	(with possible adjustment factors) to obtain a final radiance value.
91	Combined with the
92	.I \-i
93	or
94	.I \-I
95	option, irradiance contributions are reported by
96	.I \-V+
97	rather than radiance, and
98	.I \-V-
99	coefficients contain an additonal factor of PI.
100	.PP
101	The
102	.I \-c
103	option tells
104	.I rcontrib
105	how many rays to accumulate for each record.
106	The default value is one, meaning a full record will be produced for
107	each input ray.
108	For values greater than one, contributions will be averaged together
109	over the given number of input rays.
110	If set to zero, only a single record will be produced at the very
111	end, corresponding to the sum of all rays given on the input
112	(rather than the average).
113	This is equivalent to passing all the output records through a program like
114	.I total(1)
115	to sum RGB values together, but is much more efficient.
116	Using this option, it is possible to reverse sampling, sending rays from
117	a parallel source such as the sun to a diffuse surface, for example.
118	Note that output flushing via zero-direction rays is disabled with
119	.I \-c
120	set to zero.
121	.PP
122	Output flushing at fixed intervals may be enabled with the
123	.I \-x
124	option, which specifies the number of records
125	(-c accumulations) before each flush.
126	If the
127	.I \-y
128	option is also set, then periodic flushing is disabled and the
129	output size for an RGB image is the taken from the x and y dimensions.
130	In lieu of periodic flushing, a flush may be forced as mentioned above
131	by sending a sample with a zero direction vector, although you
132	must still send a full record of rays before output occurs.
133	.PP
134	If progress reports are desired, the
135	.I \-t
136	option specifies a time interval in seconds for reports sent to
137	standard error.
138	This requires that the number of input samples is known, meaning a
139	.I \-y
140	parameter has been specified.
141	.PP
142	The output of
143	.I rcontrib
144	has many potential uses.
145	Source contributions can be used as components in linear combination to
146	reproduce any desired variation, e.g., simulating lighting controls or
147	changing sky conditions via daylight coefficients.
148	More generally,
149	.I rcontrib
150	can be used to compute arbitrary input-output relationships in optical
151	systems, such as luminaires, light pipes, and shading devices.
152	.PP
153	.I Rcontrib
154	sends the accumulated rays tallies
155	to one or more destinations according to the given
156	.I \-o
157	specification.
158	If a destination begins with an exclamation mark ('!'), then
159	a pipe is opened to a command and data is sent to its standard input.
160	Otherwise, the destination is treated as a file.
161	An existing file of the same name will not be clobbered, unless the
162	.I \-fo
163	option is given.
164	If instead the
165	.I \-r
166	option is specified, data recovery is attempted on existing files.
167	(If
168	.I "\-c 0"
169	is used together with the
170	.I \-r
171	option, existing files are read in and new ray evaluations are added
172	to the previous results, providing a convenient means for
173	progressive simulation.)\0
174	If an output specification contains a "%s" format, this will be
175	replaced by the modifier name.
176	The
177	.I \-b
178	option may be used to further define
179	a "bin number" within each object if finer resolution is needed, and
180	this will be applied to a "%d" format in the output file
181	specification if present.
182	(The final integer will be offset incrementally
183	if the output is a RADIANCE picture and more than one modifier has
184	the same format specification.)\0
185	The actual bin number is computed at run time based on ray direction
186	and surface intersection, as described below.
187	The number of bins must be specified in advance with the
188	.I \-bn
189	option, and this is critical for output files containing multiple values
190	per record.
191	A variable or constant name may be given for this parameter if
192	it has been defined via a previous
193	.I \-f
194	or
195	.I \-e
196	option.
197	Since bin numbers start from zero, the bin count is always equal to
198	the last bin plus one.
199	The most recent
200	.I \-p,
201	.I \-b,
202	.I \-bn
203	and
204	.I \-o
205	options to the left of each
206	.I \-m
207	name are the ones used for that modifier.
208	Any
209	.I \-cs
210	option changing the number of spectral color
211	samples must appear before the first modifier.
212	The ordering of other options is unimportant, except for
213	.I \-x
214	and
215	.I \-y
216	if the
217	.I \-c
218	is zero, when they control the resolution string
219	produced in the corresponding output.
220	.PP
221	If a
222	.I \-b
223	expression is defined for a particular modifier,
224	the bin number will be evaluated at run time for each
225	ray contribution.
226	Specifically, each ray's world intersection point will be assigned to
227	the variables Px, Py, and Pz, and the normalized ray direction
228	will be assigned to Dx, Dy, and Dz.
229	These parameters may be combined with definitions given in
230	.I \-e
231	arguments and files read using the
232	.I \-f
233	option.
234	Additional parameter values that apply only to this modifier may be specified
235	with a
236	.I \-p
237	option, which contains a list of variable names and assigned values, separated
238	by commas, colons, or semicolons.
239	The computed bin value will be
240	rounded to the nearest whole number.
241	(Negative bin values will be silently ignored.)\0
242	For a single bin, you may specify
243	.I "\-b 0",
244	which is the default.
245	This mechanism allows the user to define precise regions or directions
246	they wish to accumulate, such as the Tregenza sky discretization,
247	which would be otherwise impossible to specify
248	as a set of RADIANCE primitives.
249	The rules and predefined functions available for these expressions are
250	described in the
251	.I rcalc(1)
252	man page.
253	Like the other rendering tools,
254	.I rcontrib
255	will search the
256	.I RAYPATH
257	library directories for each file given in a
258	.I \-f
259	option.
260	However, a special evaluation context is set for the
261	.I \-f
262	and
263	.I \-e
264	definitions, so attach a back-quote ('`') to variable and function names
265	you wish these to apply at the global evaluation level and used by all
266	materials and modifiers during rendering.
267	.PP
268	If no
269	.I \-o
270	specification is given, results are written on the standard output in order
271	of modifier (as given on the command line) then bin number.
272	Concatenated data is also sent to a single destination (i.e., an initial
273	.I \-o
274	specification without formatting strings).
275	If a "%s" format appears but no "%d" in the
276	.I \-o
277	specification, then each modifier will have its own output file, with
278	multiple values per record in the case of a non-zero
279	.I \-b
280	definition.
281	If a "%d" format appears but no "%s", then each bin will get its own
282	output file, with modifiers output in order in each record.
283	For text output, each RGB coefficient triple is separated by a tab,
284	with a newline at the end of each ray record.
285	For binary output formats, there is no such delimiter to mark
286	the end of each record.
287	.PP
288	Input and output format defaults to plain text, where each ray's
289	origin and direction (6 real values) are given on input,
290	and one line is produced per output file per ray.
291	Alternative data representations may be specified by the
292	.I \-f[io]
293	option, which is described in the
294	.I rtrace
295	man page along with the associated
296	.I \-x
297	and
298	.I \-y
299	resolution settings.
300	In particular, the color ('c') output data representation
301	together with positive dimensions for
302	.I \-x
303	and
304	.I \-y
305	will produce an uncompressed RADIANCE picture,
306	suitable for manipulation with
307	.I pcomb(1)
308	and related tools.
309	.PP
310	Options may be given on the command line and/or read from the
311	environment and/or read from a file.
312	A command argument beginning with a dollar sign ('$') is immediately
313	replaced by the contents of the given environment variable.
314	A command argument beginning with an at sign ('@') is immediately
315	replaced by the contents of the given file.
316	.PP
317	.I Rcontrib
318	supports light source contributions from photon maps generated by
319	.I mkpmap(1)
320	with its
321	.I -apC
322	option. Enabling photon mapping is described in the
323	.I rtrace
324	man page along with its relevant settings. In photon mapping mode,
325	.I rcontrib
326	only supports contributions from light sources, not arbitrary modifiers.
327	The
328	.I -b
329	option is supported along with its associated ray variables, as
330	discussed above. Ray coefficients are also supported via the
331	.I \-V-
332	option. Using fewer photons than there are light sources for the photon
333	density estimates results in omitted contributions, thus the bandwidth
334	is clamped accordingly and a warning is issued.
335	.SH EXAMPLES
336	To compute the proportional contributions from sources modified
337	by "light1" vs. "light2" on a set of irradiance values:
338	.IP "" .2i
339	rcontrib \-I+ @render.opt \-o c_%s.dat \-m light1 \-m light2 scene.oct < test.dat
340	.PP
341	To generate a pair of images corresponding to these two lights'
342	contributions:
343	.IP "" .2i
344	vwrays \-ff \-x 1024 \-y 1024 \-vf best.vf \|
345	rcontrib \-ffc `vwrays \-d \-x 1024 \-y 1024 \-vf best.vf`
346	@render.opt \-o c_%s.hdr \-m light1 \-m light2 scene.oct
347	.PP
348	These images may then be recombined using the desired outputs
349	of light1 and light2:
350	.IP "" .2i
351	pcomb \-c 100 90 75 c_light1.hdr \-c 50 55 57 c_light2.hdr > combined.hdr
352	.PP
353	To compute an array of irradiance contributions according to a Tregenza sky:
354	.IP "" .2i
355	rcontrib \-I+ \-f tregenza.cal \-b tbin \-bn Ntbins \-o sky.dat \-m skyglow
356	\-b 0 \-o ground.dat \-m groundglow @render.opt scene.oct < test.dat
357	.PP
358	To perform an annual simulation of 365 daily sun positions in photon mapping
359	mode:
360	.IP "" .2i
361	rcontrib \-I+ \-h \-V \-fo \-o c_%s.dat \-M lights \-ap contrib.pm 365
362	scene.oct < test.dat,
363	.SH ENVIRONMENT
364	RAYPATH path to search for \-f and \-M files
365	.SH BUGS
366	We do not currently compute contributions or coefficients properly
367	in scenes with participating media.
368	A single warning will be issued if a scattering or absorbing medium
369	is detected.
370	.SH AUTHOR
371	Greg Ward
372	.SH "SEE ALSO"
373	cnt(1), dctimestep(1), genklemsamp(1), getinfo(1), mkpmap(1), pcomb(1), pfilt(1),
374	pvsum(1), ra_rgbe(1), rcalc(1), rcomb(1), rfluxmtx(1), rmtxop(1), rpict(1),
375	rsensor(1), rtrace(1), rxfluxmtx(1), total(1), vwrays(1), ximage(1)
376