POV-Ray : Newsgroups : povray.bugreports : crand is not thread safe in any >=3.7 version. Do we care? : Re: crand is not thread safe in any >=3D3.7 version. Do we care? Server Time
20 Sep 2021 08:17:01 EDT (-0400)
  Re: crand is not thread safe in any >=3D3.7 version. Do we care?  
From: Kenneth
Date: 7 Mar 2018 18:05:00
Message: <web.5aa06efc7e4b5b1fa47873e10@news.povray.org>
(in 3.7.1 beta 9, running 2 threads-- as far as I can tell with my processor.)

I don't know if this helps:
I ran a simple 15-frame animation, of crand on a box. 800 X 600,
Render_Block_Size 80 (so that's 10 blocks across and 7.5 blocks down) Then used
frame 1 as a reference to 'difference' the others from it in Photoshop.

What I see is random blocks being identical from frame to frame, at random
locations. Sometimes only a few blocks, sometimes many. And the individual
frames have some random repeated blocks as well, which change from frame to
frame too.

(BTW, I'm thinking that these results may have some bearing on Bill's earlier
thread about SSLT and its own repeating 'block' behavior. Or maybe not.)

One other note: For crand to show up on an object, the object needs at least
*some* finish{diffuse...} amount. Full ambient or emission by itself doesn't
show it. I didn't know this until now.

#version 3.71;
global_settings {assumed_gamma 1.0}

camera {
  location  <.5, .5, -10>
  look_at   <.5, .5,  0>
  right     x*image_width/image_height
  angle 20

light_source {
  0*x                  // light's position (translated below)
  color rgb <1,1,1>    // light's color
  translate <20, 40, -20>

    pigment{rgb 1}
    finish{ambient 0 emission 0 diffuse 1 crand 1.0}

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