Playing with /dev/urandom Random Number generation and ImageMagick in C++ to visualize randomness or patterns.

random_pixel_generator_test.cpp

#include <Magick++.h>
#include <random>
#include <iostream>
#define HEIGHT 1024
#define WIDTH 1024
#define RANDOM_POINTS 786432 //75% of the area if no points would repeat                                                                                                                                                                                                                                                                                                               

using namespace Magick;
using namespace std;

/**                                                                                                                                                                                                                                                                                                                                                                                    
 This program uses the /dev/urandom generator to map integers                                                                                                                                                                                                                                                                                                                          
 into a 2D image, so that we can see if the random generator of                                                                                                                                                                                                                                                                                                                        
 the system forms any sort of visual pattern (non-random)                                                                                                                                                                                                                                                                                                                              

 See an output example here: http://i.imgur.com/vV3KAGv.png
*/

int main(int nargs, char** args) {
  Geometry g1(HEIGHT, WIDTH);

  Color WHITE = Color(MaxRGB, MaxRGB, MaxRGB, 0); //last is alpha, 0=opaque, MaxRGB=fully transparent                                                                                                                                                                                                                                                                                  
  Color BLACK = Color(0, 0, 0, 0);

  Image white_bg_image = Image(g1, WHITE);
  white_bg_image.magick("png");

  //initialize random device                                                                                                                                                                                                                                                                                                                                                           
  std::mt19937 eng((std::random_device())()); //i believe this uses /dev/urandom in macosx                                                                                                                                                                                                                                                                                             
  std::uniform_int_distribution<> dist(0, RAND_MAX); //RAND_MAX=2147483647                                                                                                                                                                                                                                                                                                             

  for (int i=0; i < RANDOM_POINTS; i++) {
    int r = dist(eng); //generates random number                                                                                                                                                                                                                                                                                                                                       
    int x= r % WIDTH;
    int y= (r / HEIGHT) % HEIGHT;
    white_bg_image.pixelColor(x, y, BLACK);
  }

  white_bg_image.write("random_generator.png");

  return 0;
}

/**                                                                                                                                                                                                                                                                                                                                                                                    
DEPENDENCY (ON MAC): brew install imagemagick                                                                                                                                                                                                                                                                                                                                          
                                                                                                                                                                                                                                                                                                                                                                                       
On other systems, after you have downloaded ImageMagick binaries, or you have compiled sources, you might want to set this on your environment                                                                                                                                                                                                                                         
MAGICK_HOME=/usr/local/Cellar/imagemagick/6.8.9-7                                                                                                                                                                                                                                                                                                                                      
MAGICK_INCLUDE=${MAGICK_HOME}/include                                                                                                                                                                                                                                                                                                                                                  
MAGICK_LIB=${MAGICK_HOME}/lib                                                                                                                                                                                                                                                                                                                                                          
                                                                                                                                                                                                                                                                                                                                                                                       
replace for the adequate paths, and hack the below BUILD line to use those variables to make path specifying easier.                                                                                                                                                                                                                                                                   
                                                                                                                                                                                                                                                                                                                                                                                       
I generated the below line in part using a tip from the ImageMagick tutorial pdf                                                                                                                                                                                                                                                                                                       
http://www.imagemagick.org/Magick++/tutorial/Magick++_tutorial.pdf                                                                                                                                                                                                                                                                                                                     
`Magick++-config --cppflags --cxxflags --ldflags --libs` will output all the flags you can pass to your compiler.                                                                                                                                                                                                                                                                      
                                                                                                                                                                                                                                                                                                                                                                                       
My g++ is actually a symlink to clang++                                                                                                                                                                                                                                                                                                                                                
                                                                                                                                                                                                                                                                                                                                                                                       
BUILD:                                                                                                                                                                                                                                                                                                                                                                                 
g++  -DMAGICKCORE_HDRI_ENABLE=0 -DMAGICKCORE_QUANTUM_DEPTH=16 -DMAGICKCORE_HDRI_EN\                                                                                                                                                                                                                         
ABLE=0 -DMAGICKCORE_QUANTUM_DEPTH=16 -DMAGICKCORE_HDRI_ENABLE=0 -DMAGICKCORE_QUANTUM_DEPTH=16 -I/usr/local/Cellar/imagemagick/6.8.9-7/include/ImageMagick-6 -\                                                                                                                                                                                                                         
L/usr/local/Cellar/imagemagick/6.8.9-7/lib -lMagick++-6.Q16 -lMagickWand-6.Q16 -lMagickCore-6.Q16 -L/usr/local/Cellar/imagemagick/6.8.9-7/lib -lMagick++-6.Q1\                                                                                                                                                                                                                         
6 -lMagickWand-6.Q16 -lMagickCore-6.Q16 -o random_generator_test random_generator_test.cpp                                                                                                                                                                                                                                                                                             
*/