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60 lines
2.0 KiB
GLSL

#version 330
/*************************************************************************************
The Sieve of Eratosthenes -- a simple shader by ProfJski
An early prime number sieve: https://en.wikipedia.org/wiki/Sieve_of_Eratosthenes
The screen is divided into a square grid of boxes, each representing an integer value.
Each integer is tested to see if it is a prime number. Primes are colored white.
Non-primes are colored with a color that indicates the smallest factor which evenly divdes our integer.
You can change the scale variable to make a larger or smaller grid.
Total number of integers displayed = scale squared, so scale = 100 tests the first 10,000 integers.
WARNING: If you make scale too large, your GPU may bog down!
***************************************************************************************/
// Input vertex attributes (from vertex shader)
in vec2 fragTexCoord;
in vec4 fragColor;
// Output fragment color
out vec4 finalColor;
// Make a nice spectrum of colors based on counter and maxSize
vec4 Colorizer(float counter, float maxSize)
{
float red = 0.0, green = 0.0, blue = 0.0;
float normsize = counter/maxSize;
red = smoothstep(0.3, 0.7, normsize);
green = sin(3.14159*normsize);
blue = 1.0 - smoothstep(0.0, 0.4, normsize);
return vec4(0.8*red, 0.8*green, 0.8*blue, 1.0);
}
void main()
{
vec4 color = vec4(1.0);
float scale = 1000.0; // Makes 100x100 square grid. Change this variable to make a smaller or larger grid.
int value = int(scale*floor(fragTexCoord.y*scale)+floor(fragTexCoord.x*scale)); // Group pixels into boxes representing integer values
if ((value == 0) || (value == 1) || (value == 2)) finalColor = vec4(1.0);
else
{
for (int i = 2; (i < max(2, sqrt(value) + 1)); i++)
{
if ((value - i*floor(float(value)/float(i))) == 0)
{
color = Colorizer(float(i), scale);
//break; // Uncomment to color by the largest factor instead
}
}
finalColor = color;
}
}