[Radiance-general] perlin noise

[Jack de Valpine]

Hi Greg,

Well at least I was on the right track as I had recommended something 
similar to Xian (transforms on the noise). (I guess this was offline 
though as I just hit reply.) I could not figure out how to generate a 
random value like this, so I was recommending that something could be 
scripted where random values could be generated with some other 
scripting language. This is much more elegant as it keeps it all 
(relatively) native and in-line to boot.

-Jack

Greg Ward wrote:
> Hi Xian,
>
> Jack is correct.  If you want the noise to appear different in 
> subsequent images, you must alter your scene description.  Probably 
> the easiest is to add some transform to the material, like so:
>
> void brightfunc random_dirt
> 10 dirt dirt.cal -t ${rand_x} ${rand_y} ${rand_z} -rx ${rand_rx} -ry 
> ${rand_ry}
> 0
> 1 0.5
>
> I am assuming an "A1" parameter of 0.5, but use whatever you like.  
> The above data may be passed in a file (say "dirt.fmt") to rcalc and 
> inserted in your scene like so:
>
> !date +%s | rcalc -e 'seed=$1/1000 - 1192290' \
>     -e 'rand_x=3000*rand(seed*1.901+3817)' \
>     -e 'rand_y=3000*rand(seed*-1.627-592)' \
>     -e 'rand_z=3000*rand(seed*9.67-5824)' \
>     -e 'rand_rx=180*rand(seed*2.083+964)' \
>     -e 'rand_ry=360*rand(seed*4.813+371)' -o dirt.fmt
>
> random_dirt plastic my_plastic
> (etc.)
>
> Since "date +%s" outputs a different number of seconds every time you 
> run it, this should give you a new transform unrelated to the last one 
> every time -- as long as you don't run them less than a second apart.
>
> Why do you want to do this, out of curiosity?
>
> -Greg
>
>> From: Jack de Valpine <jedev at visarc.com>
>> Date: October 13, 2007 7:52:14 AM PDT
>>
>> Hi Xian,
>>
>> Actually dirt.cal uses the fractal noise function: fnoise3(x,y,z). 
>> The Perlin noise function is noise3(x,y,z). You can look in dirt.cal 
>> to see how the function is used there and in rayinit.cal for library 
>> functions that are available. There are also additional functions: 
>> noise3x(x,y,z), noise3y(x,y,z) and noise3z(x,y,z). As I understand 
>> from RwR these represent the partial derivative of the Perlin noise 
>> function at the point (see RwR page 253).
>>
>> Regards,
>>
>> -Jack de Valpine
>>
>> Yun-Xian Ho wrote:
>>> Hi,
>>>
>>>
>>> I am using the dirt.cal function to generate Perlin noise, but I 
>>> would like to make a different noise pattern for each image given 
>>> the same A1 parameter. How do I do this?
>>>
>>> Thanks!
>>>
>>> --xian
>
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