Hello all, 

I am trying to create a blob object with a number of sphere, but I am
trying to place them at random. Now the following problem occurs, all
sphere are placed at the same position. The objection, of course, is to see
all the spheres. My code is as follows:

#declare bubbles = blob
{
  threshold 0.5
  #declare i = 0;
  #while (i<50)
    #declare S = seed(3415765);
    #declare X = rand(S);
    #declare Y = (rand(S)*2)+0.5;
    #declare Z = rand(S);
    sphere { <X, Y, Z>, 0.4, 0.55
      pigment { color rgb <0.8, 0.3, 0.6> }
    }
    #declare i = i + 1;
  #end
}

Any help would be appreciated, 
Koos Jan Niesink

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in news:01c1abbb$9437bf40$667dd383@etnica koos wrote:

> #declare bubbles = blob
> {
>   threshold 0.5
>   #declare i = 0;
>   #while (i<50)
>     #declare S = seed(3415765);
> 

Mogge,

Take "#declare S = seed(3415765);" out of the while loop and put it above 
"#declare bubbles=".


Ingo

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Thanks, for the help. It really works!!
I only don't get the reason why the seed declaration has to be placed
outside the while-loop. 

greetings/groeten, Koos Jan Niesink

ingo <ing### [at] homenl> schreef in artikel
<Xns### [at] povrayorg>...
> in news:01c1abbb$9437bf40$667dd383@etnica koos wrote:
> 
> > #declare bubbles = blob
> > {
> >   threshold 0.5
> >   #declare i = 0;
> >   #while (i<50)
> >     #declare S = seed(3415765);
> > 
> 
> Mogge,
> 
> Take "#declare S = seed(3415765);" out of the while loop and put it above

> "#declare bubbles=".
> 
> 
> Ingo
>

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in news:01c1abc2$cd6f19a0$667dd383@etnica koos wrote:

> Thanks, for the help. It really works!!

Gaaf he.

> I only don't get the reason why the seed declaration has to be placed
> outside the while-loop. 

#declare S= seed(7) intialises a random stream.
#declare Nr1= rand(S) takes the first random number from the stream.
#declare Nr2= rand(S) takes the second.
#declare Nr3= rand(S) the third.

Note that every time you render your scene Nr1 alway gets the same 
value. Now if you put #declare S= seed(7) inside a loop, it gets 
initialised every time the loop passes it. Thus the value of Nr1 will 
always be the same.
Put the seed outside the loop, it is only initialised once. On the first 
loop we will get the above result. On the second loop:

#declare Nr1= rand(S) takes the fourth random number from the stream.
#declare Nr2= rand(S) takes the fifth.
#declare Nr3= rand(S) the sixth.
etc.

The order of random numbers for a given seed is always the same.

Ingo

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koos <fra### [at] hotmailcom> wrote:
: I only don't get the reason why the seed declaration has to be placed
: outside the while-loop. 

  If you initialize the random number generator with the same value at
each loop, you'll get the same value from rand().
  A line like:

#declare S = seed(0);

means: "Make S a random number stream with the initial value 0". Successive
rand(S) calls will take values from that seed (and they are always the same
values).

-- 
#macro M(A,N,D,L)plane{-z,-9pigment{mandel L*9translate N color_map{[0rgb x]
[1rgb 9]}scale<D,D*3D>*1e3}rotate y*A*8}#end M(-3<1.206434.28623>70,7)M(
-1<.7438.1795>1,20)M(1<.77595.13699>30,20)M(3<.75923.07145>80,99)// - Warp -

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"ingo" <ing### [at] homenl> wrote in message
news:Xns### [at] povrayorg...
> in news:01c1abc2$cd6f19a0$667dd383@etnica koos wrote:
>
> > Thanks, for the help. It really works!!
>
> Gaaf he.
>

Dutch?

--
#local X=20*<-2,2,5>;sphere_sweep{catmull_rom_spline 6<-8,-8>1<-8,-8>1<-8,8>1<
8,-8>1<8,8>1<8,8>1translate 20*z pigment{gradient z scale 3color_map{[0rgb<0,9
,18>][1rgb 0]}}}#local K=2*z*X-X;#local R=seed(clock);blob{#while(K.x>X.x)
#local N=X+<rand(R)rand(R)1>/3;#local X=(vlength(N-K)<vlength(X-K)?N:2*X-N);
sphere{X,1,1rotate z*90}sphere{X,1,1}#end pigment{rgbt 1}interior{media{//Nekar
emission<2,4,5>*5}}hollow scale.05}//   http://nekar_xenos.tripod.com/metanoia/


---
Outgoing mail is certified Virus Free.
Checked by AVG anti-virus system (http://www.grisoft.com).
Version: 6.0.317 / Virus Database: 176 - Release Date: 2002/01/21

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in news:3c5d1fc1@news.povray.org Nekar Xenos wrote:

> Dutch?
> 

Ja.

Ingo

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Inderdaad ;-)
thanks for the explanation

In article <Xns### [at] povrayorg>, "ingo" <ing### [at] homenl>
wrote:


> in news:3c5d1fc1@news.povray.org Nekar Xenos wrote:
>> Dutch?
>> 
> Ja.
> Ingo

Post a reply to this message

"Koos Jan Niesink" <koo### [at] hotpopcom> wrote in message
news:3c5e5628$1@news.povray.org...
> Inderdaad ;-)
> thanks for the explanation
>
> In article <Xns### [at] povrayorg>, "ingo" <ing### [at] homenl>
> wrote:
>
>
> > in news:3c5d1fc1@news.povray.org Nekar Xenos wrote:
> >> Dutch?
> >>
> > Ja.
> > Ingo

Dit lyk vir my daar is heelwat meer Nederlanders hier as wat ek gedink het. Ek
vermoed hier is dalk ook 'n paar Vlaams sprekendes? Verskoon my spelling - ek is
Afrikaans.

I didn't see any [NE] on the povray.international so I never looked there
again...

--
#local X=20*<-2,2,5>;sphere_sweep{catmull_rom_spline 6<-8,-8>1<-8,-8>1<-8,8>1<
8,-8>1<8,8>1<8,8>1translate 20*z pigment{gradient z scale 3color_map{[0rgb<0,9
,18>][1rgb 0]}}}#local K=2*z*X-X;#local R=seed(clock);blob{#while(K.x>X.x)
#local N=X+<rand(R)rand(R)1>/3;#local X=(vlength(N-K)<vlength(X-K)?N:2*X-N);
sphere{X,1,1rotate z*90}sphere{X,1,1}#end pigment{rgbt 1}interior{media{//Nekar
emission<2,4,5>*5}}hollow scale.05}//   http://nekar_xenos.tripod.com/metanoia/


---
Outgoing mail is certified Virus Free.
Checked by AVG anti-virus system (http://www.grisoft.com).
Version: 6.0.317 / Virus Database: 176 - Release Date: 2002/01/21

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"koos" <fra### [at] hotmailcom> wrote in message
news:01c1abbb$9437bf40$667dd383@etnica...

<snip>

Well, you've had answers to your initial problem.

Here's a subtler trap with random streams....

#declare S1 = seed(32534);
#while(1=1)
    #declare S2 = seed(rand(S1))
    object{foo translate y*rand(S2)}
#end

Here, you get some variation for rand(S2), but not a lot. This is because the
seed to S2 is always in the range 0 -> 1, which returns a random stream with
very little variation.

Post a reply to this message

Tom Melly wrote:
> 
> #declare S1 = seed(32534);
> #while(1=1)
>     #declare S2 = seed(rand(S1))
>     object{foo translate y*rand(S2)}
> #end
> 
> Here, you get some variation for rand(S2), but not a lot. This is because the
> seed to S2 is always in the range 0 -> 1, which returns a random stream with
> very little variation.

Wait.  The way I'm reading this, the smaller the (absolute value of the)
seed is, the less the stream varies.

Please tell me that I'm misunderstanding.

If I'm not, can someone post a brief summary (my C is very bad) of why
(computer, not design decision) this is?

Deaken

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Deaken <dwy### [at] sw-techcom> wrote:
: If I'm not, can someone post a brief summary (my C is very bad) of why
: (computer, not design decision) this is?

  Perhaps seed() takes just the integer part of the given parameter?
(I don't know, I'm just guessing.)

-- 
#macro M(A,N,D,L)plane{-z,-9pigment{mandel L*9translate N color_map{[0rgb x]
[1rgb 9]}scale<D,D*3D>*1e3}rotate y*A*8}#end M(-3<1.206434.28623>70,7)M(
-1<.7438.1795>1,20)M(1<.77595.13699>30,20)M(3<.75923.07145>80,99)// - Warp -

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Warp wrote:
> 
> Deaken <dwy### [at] sw-techcom> wrote:
> : If I'm not, can someone post a brief summary (my C is very bad) of why
> : (computer, not design decision) this is?
> 
>   Perhaps seed() takes just the integer part of the given parameter?
> (I don't know, I'm just guessing.)

The docs for 3.1 say that seed() takes a float.  I can't find the relevant
part in the 3.5 docs.

Deaken

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In article <3C5FBC39.8BF959D6@sw-tech.com>, Deaken <dwy### [at] sw-techcom> 
wrote:

> Wait.  The way I'm reading this, the smaller the (absolute value of the)
> seed is, the less the stream varies.

No, the less the seed varies, the less the stream varies (from other 
streams, not internally). Since only the first random number of each 
stream is used, this means there will be some variation, but it won't be 
random.

-- 
Christopher James Huff <chr### [at] maccom>
POV-Ray TAG e-mail: chr### [at] tagpovrayorg
TAG web site: http://tag.povray.org/

Post a reply to this message

Christopher James Huff wrote:
> 
> In article <3C5FBC39.8BF959D6@sw-tech.com>, Deaken <dwy### [at] sw-techcom>
> wrote:
> 
> > Wait.  The way I'm reading this, the smaller the (absolute value of the)
> > seed is, the less the stream varies.
> 
> No, the less the seed varies, the less the stream varies (from other
> streams, not internally). Since only the first random number of each
> stream is used, this means there will be some variation, but it won't be
> random.

Okay, thanks.  That's good to know.

Just as an aside, and feel free to ignore this question, how many values
would you suggest throwing away before the streams are no longer "close"?

Deaken

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"Warp" <war### [at] tagpovrayorg> wrote in message news:3c5fc0c0@news.povray.org...
> Deaken <dwy### [at] sw-techcom> wrote:
> : If I'm not, can someone post a brief summary (my C is very bad) of why
> : (computer, not design decision) this is?
>
>   Perhaps seed() takes just the integer part of the given parameter?
> (I don't know, I'm just guessing.)

Nah - it's just that the stream created with seed(0.5) is very similiar to the
stream created with seed(0.6) - well IMHO, it certainly fits the symptoms. I
fell into this trap a couple of times. It was weird, things weren't exactly
identical, but nor were they random. All streams generated by seeds within a
range of 1 are pretty similiar.

If you want to use one stream as the seed for another, do something like

 R2 = seed(rand(R1)*1000)

Post a reply to this message

Tom Melly <tom### [at] tomandlucouk> wrote:
:>   Perhaps seed() takes just the integer part of the given parameter?
:> (I don't know, I'm just guessing.)

: Nah - it's just that the stream created with seed(0.5) is very similiar to the
: stream created with seed(0.6) - well IMHO, it certainly fits the symptoms.

  I don't think so. If you make a simple test, you'll see that there's
absolutely no difference between seed(0), seed(0.5) and seed(0.6). I have
the strong feeling that seed() takes just the integer part of the parameter.
I can try to check this from the source code.

#declare S1=seed(0.5);
#declare S2=seed(0.6);
#declare S3=seed(0);

#declare Ind=0;
#while(Ind<100)
  #declare n1 = rand(S1);
  #declare n2 = rand(S2);
  #declare n3 = rand(S3);
  #debug concat(str(rand(S1),0,17), " ",
                str(rand(S2),0,17), " ",
                str(rand(S3),0,17), " ")
  #if(n1=n2 & n2=n3) #debug "equal\n"
  #else #debug "different\n"
  #end
  #declare Ind=Ind+1;
#end

-- 
#macro M(A,N,D,L)plane{-z,-9pigment{mandel L*9translate N color_map{[0rgb x]
[1rgb 9]}scale<D,D*3D>*1e3}rotate y*A*8}#end M(-3<1.206434.28623>70,7)M(
-1<.7438.1795>1,20)M(1<.77595.13699>30,20)M(3<.75923.07145>80,99)// - Warp -

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Warp <war### [at] tagpovrayorg> wrote:
: I can try to check this from the source code.

  In express.cpp:

          case SEED_TOKEN:
            Val = stream_seed((int)Parse_Float_Param());
            break;


  I rest my case.

-- 
#macro M(A,N,D,L)plane{-z,-9pigment{mandel L*9translate N color_map{[0rgb x]
[1rgb 9]}scale<D,D*3D>*1e3}rotate y*A*8}#end M(-3<1.206434.28623>70,7)M(
-1<.7438.1795>1,20)M(1<.77595.13699>30,20)M(3<.75923.07145>80,99)// - Warp -

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On 6 Feb 2002 16:15:47 -0500, Warp wrote:
> Warp <war### [at] tagpovrayorg> wrote:
>: I can try to check this from the source code.
> 
>   In express.cpp:
> 
>           case SEED_TOKEN:
>             Val = stream_seed((int)Parse_Float_Param());
>             break;
> 
> 
>   I rest my case.

How do we know you didn't just make that up?  Just where is this express.cpp
anyway? :)

-- 
plane{-z,-3normal{crackle scale.2#local a=5;#while(a)warp{repeat x flip x}rotate
z*60#local a=a-1;#end translate-9*x}pigment{rgb 1}}light_source{-9red 1rotate 60
*z}light_source{-9rgb y rotate-z*60}light_source{9-z*18rgb z}text{ttf"arial.ttf"
"RP".01,0translate-<.6,.4,.02>pigment{bozo}}light_source{-z*3rgb-.2}//Ron Parker

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Ron Parker <ron### [at] povrayorg> wrote:
: How do we know you didn't just make that up?  Just where is this express.cpp
: anyway? :)

  It's identical to how it's done in express.c in the POV-Ray 3.1g source
(anyone can check this), and for now you only have to trust me that this
hasn't been changed in the 3.5 source code (it can be checked when the
source is released). :)

  (Of course "you" here is in plural. Naturally you, Ron, can check it
right away. :) )

-- 
#macro M(A,N,D,L)plane{-z,-9pigment{mandel L*9translate N color_map{[0rgb x]
[1rgb 9]}scale<D,D*3D>*1e3}rotate y*A*8}#end M(-3<1.206434.28623>70,7)M(
-1<.7438.1795>1,20)M(1<.77595.13699>30,20)M(3<.75923.07145>80,99)// - Warp -

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> Dit lyk vir my daar is heelwat meer Nederlanders hier as wat ek gedink het. Ek
> vermoed hier is dalk ook 'n paar Vlaams sprekendes? Verskoon my spelling - ek
is
> Afrikaans.
Flemish is almost the same as Dutch, that's why most people refer to both
languages as Dutch. I don't really agree with this.  In my opinion, Dutch
resembles Flemish not much more than it resembles Afrikaans. (please, don't
start a discussion about it, I'm tired of those discussions...)

nog ne goeiendag!
--
camera{location-z*3}#macro G(b,e)b+(e-b)*(C/50)#end#macro L(b,e,k,l)#local C=0
;#while(C<50)sphere{G(b,e),.1pigment{rgb G(k,l)}finish{ambient 1}}#local C=C+1
;#end#end L(y-x,y,x,x+y)L(y,-x-y,x+y,y)L(-x-y,-y,y,y+z)L(-y,y,y+z,x+y)L(0,x+y,
<.5,1,.5>,x)L(0,x-y,<.5,1,.5>,x)               // ZK http://www.povplace.be.tf

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in news:3c619c12@news.povray.org Warp wrote:

> I have
> the strong feeling that seed() takes just the integer part of the
> parameter. 

I'll change that in the docs (12)

Ingo

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"Warp" <war### [at] tagpovrayorg> wrote in message news:3c619d02@news.povray.org...
>
>   I rest my case.
>

Ah! Is this intended?

My impression was wrongly formed by placing several randomly generated objects
next to each other. The different viewpoints was just enough to convince me that
there were minor differences.

Still, the original point remains, R2 = seed(rand(R1)) is still a waste of time.

Post a reply to this message

Tom Melly <tom### [at] tomandlucouk> wrote:
: Ah! Is this intended?

  I would guess that the random number generator algorithm used in povray
uses just integers.

-- 
#macro M(A,N,D,L)plane{-z,-9pigment{mandel L*9translate N color_map{[0rgb x]
[1rgb 9]}scale<D,D*3D>*1e3}rotate y*A*8}#end M(-3<1.206434.28623>70,7)M(
-1<.7438.1795>1,20)M(1<.77595.13699>30,20)M(3<.75923.07145>80,99)// - Warp -

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