"Bald Eagle" <cre### [at] netscapenet> wrote:
>...
> Obviously there have been many requests for vector functions, and that leads me
> to bring this up:
> #macro eval_pigment(pigm, vec)
>     #local fn = function { pigment { pigm } }
>     #local result = (fn(vec.x, vec.y, vec.z));
>     result
> #end
>
> Somehow this magically returns a vector quantity, rather than a scalar.  :O

Bill,

Have you seen these sections in the documentation ?

Declaring User-Defined Vector Functions
https://www.povray.org/documentation/3.7.0/r3_3.html#r3_3_1_8_4

Declaring User-Defined Color Functions
https://www.povray.org/documentation/3.7.0/r3_3.html#r3_3_1_8_5

--
Tor Olav
http://subcube.com
https://github.com/t-o-k

Post a reply to this message

"Tor Olav Kristensen" <tor### [at] TOBEREMOVEDgmailcom> wrote:

> Bill,
>
> Have you seen these sections in the documentation ?
>
> Declaring User-Defined Vector Functions
> https://www.povray.org/documentation/3.7.0/r3_3.html#r3_3_1_8_4
>
> Declaring User-Defined Color Functions
> https://www.povray.org/documentation/3.7.0/r3_3.html#r3_3_1_8_5

Aye, I have, I have used the spline functions, and intuitively knew about the
pigment functions, but have spent so much time with scalar-only functions, that
it just struck me as --- odd and unexpected.


Good to see you around and poking your head in.    I hope all is going well in
your part of the world, and you have been finding ways to enjoy yourself amidst
- everything.

Post a reply to this message

"Bald Eagle" <cre### [at] netscapenet> wrote:
>...
> Good to see you around and poking your head in.    I hope all is going well in
> your part of the world, and you have been finding ways to enjoy yourself amidst
> - everything.

I'm lurking around in here in periods, but I seldom have as much time to
contribute as I would like. What is happening here is often interesting and
thought provoking. And sometimes very nice images appear ! So it is very good
that you and others keep this forum alive over time.

All is well here, thank you, except, of course, from the COVID-19 pandemic.
The Corona virus has not (yet) caused such big problems here in Norway as it has
in many other parts of the world. I hope all is well with you too Bill.

--
Best regards
Tor Olav
http://subcube.com
https://github.com/t-o-k

Post a reply to this message

"Tor Olav Kristensen" <tor### [at] TOBEREMOVEDgmailcom> wrote:

> I'm lurking around in here in periods, but I seldom have as much time to
> contribute as I would like.

Of course.  I hope you enjoy what you do and your field of work is flourishing.

Most of my work gets done in fits and starts and flashes of inspiration.  Rest
assured that much of what you have done to help myself and others clarify key
concepts and make it over hurdles we were struggling with has been of great
value.   Every snippet of code, equation, macro, or even a single 9-character
line of code is something to be used, learned from, and transferred on to others
climbing the same ladder.

> What is happening here is often interesting and
> thought provoking. And sometimes very nice images appear ! So it is very good
> that you and others keep this forum alive over time.

Indeed, there is still development happening across the spectrum - from
fundamental equations, algorithms, and other under-the-hood work to the
glistening final renders of stalwarts and masters.

> All is well here, thank you, except, of course, from the COVID-19 pandemic.
> The Corona virus has not (yet) caused such big problems here in Norway as it has
> in many other parts of the world. I hope all is well with you too Bill.


It all seems to be part of the cunning game taking place on the Grand
Chessboard.  The way I see it, "COVID-19" hasn't created any problems over and
above any of the other diseases that have ever arisen over the years, but
certainly the [over]reactions to it HAVE.

All is never "well" - but I have learned from many of the people who have
offered me insight and wisdom over the years that adversity and a bit of
hardship keep the mind and body healthy.

"...technology alone didn't allow humans to go to Madagascar, to Australia.
Neanderthals built boats too. Instead, he says, there's "some madness there. How
many people must have sailed out and vanished on the Pacific before you found
Easter Island? I mean, it's ridiculous. And why do you do that? Is it for the
glory? For immortality? For curiosity? And now we go to Mars. We never stop."
It's ridiculous, foolish, maybe? But it was the Neanderthals who went extinct,
not the humans.”"

“Maybe it's only a fool who will perilously journey out to what might not be
there. And maybe it's only a fool who will ask about supertasks, about infinity.
But if you want to solve problems, you don't just solve the ones that are there,
you find more and make more and go after the impossible ones; fostering a love
and obsession with problems is how you solve problems. Antoine de Saint-Exupéry
wasn't a mathematician, but his advice fits nicely here. If you want to build a
ship, don't drum up people to collect wood and don't assign them tasks and work,
but rather teach them to long for the endless immensity of the sea."

- Michael Stevens

Post a reply to this message

hi,

William F Pokorny <ano### [at] anonymousorg> wrote:
> On 8/2/20 7:33 PM, jr wrote:
> > ...
> > another "interesting" thing is the output of 'ps'.  a big difference in the
> > virtual memory size, 'povr' barely 2% of POV-Ray's size.  and, puzzling this,
> > while the thread count ('nlwp') for POV-Ray fluctuates (6 to 10), 'povr's always
> > reads 1.
> ...
> First the obvious, might you have been looking at 'povr' the script and
> not the real running povray command? Otherwise I'm not completely sure.
> ...

thanks, yes.  I forgot/overlooked that the executable is invoked from a script.
:-(


regards, jr.

Post a reply to this message

Le 03/08/2020 à 19:43, Bald Eagle a écrit :
> I haven't had much time to explore all of the forks and other projects - but
> while they are under development, maybe I could throw some old and new ideas
> out.
> 
> SO many people have asked to have values like the camera location be available.
> 

And nobody looked at hgpovray:

http://wiki.povray.org/content/User:Le_Forgeron/cameras#Access_to_camera_information

> http://wiki.povray.org/content/User:Le_Forgeron/cameras#Access_to_camera_information




> As it is a vector, having the ability to have such a value be translated,
> rotated, etc. and then queried for the result reminds me that having a point or
> vector object that can be manipulated using standard SDL commands would be very
> useful for a lot of folks who need to do that kind of thing.

Only if such "object" could be queried. It would have to distinguish
between points (3D vector) and normal (also 3D vector) at a given location.

On the other hand, the answer of Tor is fine: you can already have a
transform object and process vectors in it.

> 
> Working on Yadgar's code, I realized that it might be an interesting and useful
> thing to be able to access the current memory usage and the current number of
> tokens parsed - for reporting, but also to define a bailout so as not to crash
> the system, etc.

That could be considered, a bit like "now", the variable which returns
the current number of seconds since 2000-1-1 0:0:0 GMT.

* number of parsed token is a local data, just to find it in the code
(as it is currently reported by the parser, it must exist somewhere).

* current memory usage, I have a problem: how do you get that piece of
information, in a portable/Posix way ?
** Linux/Unix could use sysinfo()
** Windows could use GetProcessMemoryInfo(GetCurrentProcess(), ... )
** Mac could use task_info(mach_task_self(), ... )

If you want to protect your system from memory exhaustion, it is better
to ask the system to do it, or delegate to some tools between the system
and povray.



> 
> Obviously there have been many requests for vector functions, and that leads me
> to bring this up:
> #macro eval_pigment(pigm, vec)
>     #local fn = function { pigment { pigm } }
>     #local result = (fn(vec.x, vec.y, vec.z));
>     result
> #end
> 
> Somehow this magically returns a vector quantity, rather than a scalar.  :O
> 
> Matrix objects would be very nice for certain 3D graphics calculations and
> transformations.  Maybe a matrix convolution function for image processing.  I
> can see this being closely related to the recent work on function gradients as
> well.

There is already "transform" & "matrix" , but they are targeted to 3D
operations, using weighted coordinates (4x4, but you do not get to
specify the last column)

Convolution matrices are 2D filters, this is nothing related to our
matrices, it could be a totally new domain of exploration.

> 
> 1D and 2D fast Fourier transforms.
> Paul Bourke already has 2D in-place FFT code in c++ posted on his site.
> http://paulbourke.net/miscellaneous/dft/
> 

Und ich sage "Warum ?"

Fourier transforms are used with sampling (and fixed number of values).
It is lovely in Jpeg and other compressions, but what would be the usage
in a 3D rendering program ?

Wavelet (compression) also had its time of hype, yet it seems unrelated
to 3D rendering.


> Just throwing out ideas, as these are inherently source code edits and
> additions.
> 
> 

Ok, I note there is one remaining point that could be interesting:
getting the current number of parsed tokens.
Does not seem so urgent as a change.

Post a reply to this message

Le_Forgeron <jgr### [at] freefr> wrote:

> And nobody looked at hgpovray:

I have and I do.   I have a tab open in my browser right now:
https://github.com/LeForgeron/povray/releases/tag/v3.8.0.alpha%2BHg.228.Jasmin
because it's going to get installed on my "new" laptop.

But I was mentioning this with an eye toward implementing it in official
pov-ray, the argument being, "If the code exists, and it works, and no one has
discovered any bugs - then what are the excuses left to NOT implement it?"
And if hgpovray has it AND povr has it, ....?


> Only if such "object" could be queried. It would have to distinguish
> between points (3D vector) and normal (also 3D vector) at a given location.

No, because it would be a proper object.
point {<vector>}
Then you could do translate <-1, 3, 9> and rotate -x*45
and then do a standard min_extent max_extent "query" on its location.

This would be useful for collections of points in a union that define important
points in/on an object.  Like a rotating gear or a chain or whatever one might
like to have a usable data point to plug into an equation.


> On the other hand, the answer of Tor is fine: you can already have a
> transform object and process vectors in it.

You can, but it's --- awkward.   I _can_ do certain things with macros and
functions, but it's not anywhere near as straightforward as if I were just
driving forward with aliases and vector functions.



> That could be considered, a bit like "now", the variable which returns
> the current number of seconds since 2000-1-1 0:0:0 GMT.

Yes, sure - that makes sense.

> * number of parsed token is a local data, just to find it in the code
> (as it is currently reported by the parser, it must exist somewhere).

Well it ticks off at the bottom of qtpovray and presumably windows, so I just
assumed that it was available at any given moment.

> * current memory usage, I have a problem: how do you get that piece of
> information, in a portable/Posix way ?

IIRC, the windows editor displays that information during parsing, so someone
has already done it?


> If you want to protect your system from memory exhaustion, it is better
> to ask the system to do it, or delegate to some tools between the system
> and povray.

Yes, but for some people, that's a whole other skill set and learning curve and
time sink that takes away from writing the scene.   It was just a small
suggestion that I thought could be useful if it could be trivially implemented.


> There is already "transform" & "matrix" , but they are targeted to 3D
> operations, using weighted coordinates (4x4, but you do not get to
> specify the last column)

Yes - I meant in a general sense.  Data structures and tools where one could
create normal mathematical matrices and do all of the usual matrix math
operations.   I know that we have _some_ macros for that, and I have written
quite a few of my own, but having a more complete, formal set of tools for this
would be nice - there are a lot of people who use povray for math and graphics,
and want to use it as a tool to do creative work and understand an
illustrate/demonstrate the underlying processes.

> Convolution matrices are 2D filters, this is nothing related to our
> matrices, it could be a totally new domain of exploration.

They are.  I envision a lot of interesting things that people could do, using
them as image_map modifiers in order to process terrain and even procedural
pigment patterns.


> > 1D and 2D fast Fourier transforms.
> > Paul Bourke already has 2D in-place FFT code in c++ posted on his site.
> > http://paulbourke.net/miscellaneous/dft/
> >
>
> Und ich sage "Warum ?"

as did clipka.

> Fourier transforms are used with sampling (and fixed number of values).
> It is lovely in Jpeg and other compressions, but what would be the usage
> in a 3D rendering program ?

Because povray is uniquely a DATA driven rendering software where things are
made programmatically, not with a modeler.  And of course a vast amount of the
data we deal with is procedural.  Patterns.  Signals, if you will.  And so the
single-most useful signal-processing algorithm ever conceived could (and would)
be used to create, analyze, and filter data sets for use in making patterns, and
creating the necessary geometry to be textured and rendered.
People have already played with making object shapes with fourier.   jpg has
color banding that someone may want to know the periodicity of.   procedural
patterns and various fractal textures may have repeats that one may need to know
the frequency of in order to avoid/hide.   Procedural patterns are _patterns_
And everything we do is based on patterns.   Chris Cason mentioned that people
use povray as part of their workflow.  I corresponded somewhat recently with
someone who was in fact using fourier to do work on x-ray crystallographic data.
 Mathematicians and scientists would surely find this otherwise ubiquitous tool
useful and we may get new users who discover povray itself - not as a and
end-of-pipeline rendering tool, but as a curiosity and hobby.   This is how we
get new people and ideas.   Lots of scientific data gets processed and
visualized with povray - it's information.  Signals.
I almost see this as being akin to "of what use would something like Perlin
noise be to 3D graphics...?"



> Wavelet (compression) also had its time of hype, yet it seems unrelated
> to 3D rendering.

Unfamiliar with that.


> Does not seem so urgent as a change.

These are suggestions for the interested to consider.   Not any "urgent"
features that I'm hounding anyone to do right now.

Post a reply to this message

Le 04/08/2020 à 10:26, Le_Forgeron a écrit :
> Ok, I note there is one remaining point that could be interesting:
> getting the current number of parsed tokens.
> Does not seem so urgent as a change.

For the curious, the value is in parser/parser.h : mTokenCount

Now, can someone provide a good name for the SDL to return that value ?

Post a reply to this message

hi,

Le_Forgeron <jgr### [at] freefr> wrote:
> Le 04/08/2020 à 10:26, Le_Forgeron a écrit :
> > Ok, I note there is one remaining point that could be interesting:
> > getting the current number of parsed tokens.
> > Does not seem so urgent as a change.
>
> For the curious, the value is in parser/parser.h : mTokenCount
>
> Now, can someone provide a good name for the SDL to return that value ?

some new function modelled on 'sysconf(3)' would be cool, with 'mTokenCount'
just one of the argument values, perhaps.


regards, jr.

Post a reply to this message

Le_Forgeron <jgr### [at] freefr> wrote:

> Now, can someone provide a good name for the SDL to return that value ?

token_count
tokens_current
parsed_tokens
object_tokens
parser_tokens
current_tokens
tokens_now()

HowMuchStuffIHaveParsedSoFar

:D

Post a reply to this message

Le 20/08/2020 à 00:22, Bald Eagle a écrit :
> Le_Forgeron <jgr### [at] freefr> wrote:
> 
>> Now, can someone provide a good name for the SDL to return that value ?
> 
> token_count
> tokens_current
> parsed_tokens
> object_tokens
> parser_tokens
> current_tokens
> tokens_now()
> 
> HowMuchStuffIHaveParsedSoFar
> 
> :D
> 
Adopted "parsed_tokens"


=======
#version 3.8;
global_settings {assumed_gamma 1.0}
#include "colors.inc"
#default{ finish{ ambient 0.1 diffuse 0.9 }}


light_source { <100,1000,-1000>, White}

camera { location <0,-1,-16>
         right    x*image_width/image_height
         angle 35
         look_at <0,-1,0>
       }

plane{-z,-10  pigment{checker color rgb<1,1,1>*0.8 color rgb<1,1,1>} }

#declare String1=concat("parsed_tokens =", str(parsed_tokens,0,0));


text{ internal 1, "Parser info", 0.3, 0 pigment{Blue*0.7} translate
-4.5*x+1.5*y }
text{ internal 1, String1, 0.3, 0 pigment{Red*0.7} translate -4.5*x }
#declare String2=concat("parsed_tokens =", str(parsed_tokens,0,0));
#declare String3=concat("parsed_tokens =", str(parsed_tokens,0,0));
text{ internal 1, String2, 0.3, 0 pigment{Red*0.7} translate -4.5*x -1.5*y }
text{ internal 1, String3, 0.3, 0 pigment{Red*0.7} translate -4.5*x -3*y }

Post a reply to this message

Le 19/08/2020 à 21:27, jr a écrit :
> hi,
> 
> Le_Forgeron <jgr### [at] freefr> wrote:
>> Le 04/08/2020 à 10:26, Le_Forgeron a écrit :
>>> Ok, I note there is one remaining point that could be interesting:
>>> getting the current number of parsed tokens.
>>> Does not seem so urgent as a change.
>>
>> For the curious, the value is in parser/parser.h : mTokenCount
>>
>> Now, can someone provide a good name for the SDL to return that value ?
> 
> some new function modelled on 'sysconf(3)' would be cool, with 'mTokenCount'
> just one of the argument values, perhaps.
> 
> 

You know what is bad with such idea ?
1. Look at the map type in image_map: using number instead of explicit
good name is painful, even when Constants.inc provides some name afterward.

http://wiki.povray.org/content/Reference:Image_Map

2. sysconf is a pain to use: you always need to be on the local system
to be sure to get what you ask (the man page of sysconf is using
symbolic constants, which do not translate at all between systems once
compiled). Initially I thought you wanted access to sysconf, but it
seems to only be a model.

3. it is too open: there is no usable specification.
It is like "add a foo(bar) function which return mTokenCount when bar is 3"
Why having such function ? What would be the common part with the value
returned when bar is 5 ?
Also Povray loves floating point values, and hates integer, so what is
the meaning of foo(3.4) ?
It reminds me far too much of the poke & peek tables in the 80's computers.

To misname things is to add to the unhappiness of the world.

Post a reply to this message

Le_Forgeron <jgr### [at] freefr> wrote:

> You know what is bad with such idea ?
> 1. Look at the map type in image_map: using number instead of explicit
> good name is painful, even when Constants.inc provides some name afterward.

Yes.  I would agree that a good (but SHORT) name would be best.
But I have also come to value the ability to refer to things numerically, so
that I can loop through a collection of things easily - we people love
descriptive, meaningful names - computers love numbers.

Wih respect to image_map specifically, any guesses as to what the missing map
types were supposed to be?  :D

> Initially I thought you wanted access to sysconf, but it
> seems to only be a model.

I think he was interested in having a "povray system function" that would be
able to return a number of different system / environment / configuration values
- LIKE sysconf.
So perhaps some of the internal epsilon values, memory available, threads used,
etc.   Someone might want to annotate their render or generate a text file that
gets post-render bundled with their render for documentation purposes.
Development, debugging, documenting - and they may want/need to do that with a
programmable function - like if they have 3000 frames - and avoid having to drag
another software/OS tool (and learning curve) into the mix.

> To misname things is to add to the unhappiness of the world.

Yeah, brother.  No truer words were ever spoken.  Say what you mean, and mean
what you say. (Or at least try as much as possible/practical)

Post a reply to this message

hi,

Le_Forgeron <jgr### [at] freefr> wrote:
> ...
> 2. sysconf .... Initially I thought you wanted access to sysconf, but it
> seems to only be a model.

yes, just a function with an interface like 'sysconf()'.  Bald Eagle put it
better than I could.

> ...
> To misname things is to add to the unhappiness of the world.

agree, and yet, finding "good" descriptive names is never easy (for me, anyway).


regards, jr.

Post a reply to this message

On 8/23/20 1:38 PM, Bald Eagle wrote:
> Le_Forgeron <jgr### [at] freefr> wrote:
> 
...
> 
> Wih respect to image_map specifically, any guesses as to what the missing map
> types were supposed to be?  :D
> 

I ran across the following in the v1.0 source code the other day while 
trying to understand the history of something:

/* Image/Bump Map projection methods */
#define PLANAR_MAP      0
#define SPHERICAL_MAP   1
#define CYLINDRICAL_MAP 2
#define PARABOLIC_MAP   3
#define HYPERBOLIC_MAP  4
#define TORUS_MAP       5
#define PIRIFORM_MAP    6
#define OLD_MAP         7

I guess v3.8's type 7 (angular light probe?) took OLD_MAP's slot :-).

The documentation has forever said types 3 & 4 are under development, 
but I've never spotted any actual code indicating this ever true beyond 
an intent. FWIW.

Bill P.

Post a reply to this message

William F Pokorny <ano### [at] anonymousorg> wrote:

> I ran across the following in the v1.0 source code the other day while
> trying to understand the history of something:
>
> /* Image/Bump Map projection methods */
> #define PLANAR_MAP      0
> #define SPHERICAL_MAP   1
> #define CYLINDRICAL_MAP 2
> #define PARABOLIC_MAP   3
> #define HYPERBOLIC_MAP  4
> #define TORUS_MAP       5
> #define PIRIFORM_MAP    6
> #define OLD_MAP         7

VERY cool  :)
It's more than clipka uncovered.
So at least that answers a 6-year-old question.  :D

http://news.povray.org/povray.binaries.images/message/%3C5438051b%241%40news.povray.org%3E/#%3C5438051b%241%40news.povr
ay.org%3E

Are these mapping types still in need of development?

Post a reply to this message

On 8/24/20 1:35 PM, Bald Eagle wrote:
> William F Pokorny <ano### [at] anonymousorg> wrote:
> 
...
> 
> Are these mapping types still in need of development?
> 

None can be that important given how long they've not been done! :-)

Guessing a  at meaning/application, the parabolic I suppose might 
occasionally be of use - parabolas. Taking the hyperbolic to mean 
non-linear in some aspect of other usually linear mappings, that I guess 
that would end up as a set of 'hyper' mappings for linear, spherical, 
etc. Piriform suppose might have been aimed at two element blobs or 
something?

My up front issue with all more complicated mappings - and with the more 
complicated shape uv_mapping options - is one should first and foremost 
work out how the maps can easily be created in POV-Ray(1). Or, know of 
some standard external 'standard' like the light probe angular mapping 
added to v3.8. Otherwise, you've got some feature you can 'advertise' 
and which might look great for a demo or two, but in the end it's a 
feature pretty much nobody uses.

(1) - Matching cameras, an interactive painting capability, ...

Aside: Most any complicated mapping can be accomplished today via 
functions - though it might not be easy to get right, as you well know.

Bill P.

Post a reply to this message

William F Pokorny <ano### [at] anonymousorg> wrote:

> None can be that important given how long they've not been done! :-)

Well, yes.   There's that.
But one might equally ascribe their non-usage to their non-existence.

Given an easy way to do something, people usually take it.
If faced with the prospect of somehow getting someone somewhere to write a
mapping in source code and provide a new release - or - just writing some "good
enough" pseudo-mapping or function-mapping, then maybe that's what's been done.
No idea how many people (would have) use(d) those other types of maps, but
possibly that would tip the scales the other way.

It's always hard to speculate about these things accurately.  ;)

> Guessing a  at meaning/application, the parabolic I suppose might
> occasionally be of use - parabolas.

I guess maybe there might be further use with parabolic mirrors, cameras, and -
more specifically - telescopes.

https://www.eso.org/sci/facilities/paranal/telescopes/vlti/tuto/tutorial_introduction_to_stellar_interf.pdf

> Taking the hyperbolic to mean
> non-linear in some aspect of other usually linear mappings, that I guess
> that would end up as a set of 'hyper' mappings for linear, spherical,
> etc.

I looked - it seems like they might be very useful and fun for Escher fans.
M. Grimbert might be interested, given he seems to be the master of tilings.
I'm guessing/speculating that these mappings (Poincare disks, etc) might have
practical engineering / scientific use in physics, Finite Element Methods, fluid
dynamics, etc?

https://computergraphics.stackexchange.com/questions/2117/map-a-texture-onto-a-hyperbolic-triangle
https://medium.com/@philogb/hyperbolic-floors-a2c5445144c6
https://mediatum.ub.tum.de/doc/1210572/1210572.pdf

Or maybe it has specific application to cartography and map projections?
https://en.wikipedia.org/wiki/Squeeze_mapping

It might also be related to a catadioptric omnidirectional camera mapping, like
that used with a hyperbolic convex mirror.
https://link.springer.com/content/pdf/10.1007%2F978-3-642-02921-9_26.pdf

And this leads me to believe that they are all related:
http://roguetemple.com/z/hyper/models.php



> Piriform suppose might have been aimed at two element blobs or
> something?

Possibly.   No idea why it was desired in v 1 of all things, and the only places
I find it aside from pure math sites, is references for POV-Ray (with Mike
Williams bridging that gap)
https://mathworld.wolfram.com/PiriformCurve.html
https://mathworld.wolfram.com/PiriformSurface.html

>
> My up front issue with all more complicated mappings - and with the more
> complicated shape uv_mapping options - is one should first and foremost
> work out how the maps can easily be created in POV-Ray(1). Or, know of
> some standard external 'standard' like the light probe angular mapping
> added to v3.8. Otherwise, you've got some feature you can 'advertise'
> and which might look great for a demo or two, but in the end it's a
> feature pretty much nobody uses.
>
> (1) - Matching cameras, an interactive painting capability, ...
>
> Aside: Most any complicated mapping can be accomplished today via
> functions - though it might not be easy to get right, as you well know.

Of course.   But sometimes these things inexplicably take on a life of their
own.  And during the course of investigating them simply out of curiosity,
novelty, or someone's specialized interest or based solely on the challenge of
doing it - we uncover bugs (!) and discover interesting new things that we might
never have thought of or even known were possible.

Just figured I'd ask - because obviously _someone_ thought they were important
enough to assign a mapping slot for them early on.

##############################################################################

Now, given the fact that we have uv-mapping for Bezier bicubic patches, and the
source code to create the patch from the corners and control points:

Do we think it would be a lot of work to add a feature where
colors/pigments/textures/finishes could be specified at the corners of a Bezier
patch, and a pattern / map would be generated based on the patch?
https://www.ibiblio.org/e-notes/Splines/color3d.html
(I didn't SEE such a thing in HGpovray38, but I might have missed it)

Post a reply to this message

> 
>
https://computergraphics.stackexchange.com/questions/2117/map-a-texture-onto-a-hyperbolic-triangle
> https://medium.com/@philogb/hyperbolic-floors-a2c5445144c6
> https://mediatum.ub.tum.de/doc/1210572/1210572.pdf


An investigation not as pattern but as warp could be interesting.

The early part to answer is: what happen outside the circle.
One answer can be: nothing, outside the circle, there is no transformation.

Or something different, as suggested in the pdf for poincarré disk.

It is "of course" to be mainly used with the image pattern, so it is
better from the very start that the reference plane be the same (to
avoid a systematic rotate), and the third coordinates is to be dropped.

So far the "perfect" illustration could be some pedestal table with such
topping, and some chess set on it...
With an outer ring, which implies some layered textures too.

*********

About bezier bicubic patches, I do not so far understand what is the
final purpose of the request. Does it sound like gluing the mesh camera
to a bezier bicubic patch ? (mesh camera or user-function defined camera).
As a raytracing aims at generating pictures, what is a finish map in
that context ?

Post a reply to this message

Le_Forgeron <jgr### [at] freefr> wrote:

> An investigation not as pattern but as warp could be interesting.

Aha, yes - that's a better way of thinking about it.

> The early part to answer is: what happen outside the circle.
> One answer can be: nothing, outside the circle, there is no transformation.

That would be my initial, naive impression.  Something like "once".

> Or something different, as suggested in the pdf for poincarré disk.

I'm sure that there exist a number of different options, and of course we will
probably find out what they are once someone picks up this sort of thing to
begin experimenting with and proceeds to discover what other ways there are or
follows a path of reasoning to suggest a new option.

Geometric inversion?

> It is "of course" to be mainly used with the image pattern, so it is
> better from the very start that the reference plane be the same (to
> avoid a systematic rotate), and the third coordinates is to be dropped.

Oh, please, no.   One of my main dislikes of things like prism {} is that the
coordinates are supplied in <x, z> format.  So then rather than simply passing
[multipurpose] vectors to the object definition, where the y-component gets
_ignored_, I have to write a whole new section of code to convert everything
into a special single-purpose format.   :(

> So far the "perfect" illustration could be some pedestal table with such
> topping, and some chess set on it...
> With an outer ring, which implies some layered textures too.

Likely.  But I also envisioned seeing how all of the various tilings can be
manipulated.   :)

> About bezier bicubic patches, I do not so far understand what is the
> final purpose of the request. Does it sound like gluing the mesh camera
> to a bezier bicubic patch ? (mesh camera or user-function defined camera).
> As a raytracing aims at generating pictures, what is a finish map in
> that context ?

The idea would be to define 4 corners of the bezier patch in terms of - not
<x,y,z> - but <r, g, b> and then rather than doing a straight bilinear
interpolation of the color values between the two points across the rectangle,
bicubically interpolate the colors across a Bezier surface.
Does that make sense?

I guess I also had it in my mind that if I had an existing _geometric_ bezier
patch, that somehow it would be possible to simply define the colors of the 4
fixed corners, and those would get mapped to the geometric coordinates.   Then
the geometric control points would control the bicubic color interpolation
between the color values - avoiding the need to write a whole separate block of
code for the coloring.

I hadn't really though it all the way through, so sorry for any confusion.

But it does suggest that there could be a bicubic WARP where patterns could be
distorted (or image maps corrected) through such a mechanism.

Also, the mesh camera is an interesting idea.  I'm not sure what you mean by the
finish map - but I would imagine it has something to do with the
ray-scene/surface angles?   Like for something simple like specular reflection?
That I simply don't know.
Maybe if it were just an experimental feature, use the undistorted mesh camera
to generate the color but the bicubic functions to control the view....
No idea.

Post a reply to this message