Pods/GPUImage/framework/Source/GPUImageKuwaharaFilter.m
#import "GPUImageKuwaharaFilter.h"

// Sourced from Kyprianidis, J. E., Kang, H., and Doellner, J. "Anisotropic Kuwahara Filtering on the GPU," GPU Pro p.247 (2010).
// 
// Original header:
// 
// Anisotropic Kuwahara Filtering on the GPU
// by Jan Eric Kyprianidis <www.kyprianidis.com>

#if TARGET_IPHONE_SIMULATOR || TARGET_OS_IPHONE
NSString *const kGPUImageKuwaharaFragmentShaderString = SHADER_STRING
(
 varying highp vec2 textureCoordinate;
 uniform sampler2D inputImageTexture;
 uniform int radius;
 
 precision highp float;
 
 const vec2 src_size = vec2 (1.0 / 768.0, 1.0 / 1024.0);
 
 void main (void) 
 {
     vec2 uv = textureCoordinate;
     float n = float((radius + 1) * (radius + 1));
     int i; int j;
     vec3 m0 = vec3(0.0); vec3 m1 = vec3(0.0); vec3 m2 = vec3(0.0); vec3 m3 = vec3(0.0);
     vec3 s0 = vec3(0.0); vec3 s1 = vec3(0.0); vec3 s2 = vec3(0.0); vec3 s3 = vec3(0.0);
     vec3 c;

     for (j = -radius; j <= 0; ++j)  {
         for (i = -radius; i <= 0; ++i)  {
             c = texture2D(inputImageTexture, uv + vec2(i,j) * src_size).rgb;
             m0 += c;
             s0 += c * c;
         }
     }

     for (j = -radius; j <= 0; ++j)  {
         for (i = 0; i <= radius; ++i)  {
             c = texture2D(inputImageTexture, uv + vec2(i,j) * src_size).rgb;
             m1 += c;
             s1 += c * c;
         }
     }

     for (j = 0; j <= radius; ++j)  {
         for (i = 0; i <= radius; ++i)  {
             c = texture2D(inputImageTexture, uv + vec2(i,j) * src_size).rgb;
             m2 += c;
             s2 += c * c;
         }
     }

     for (j = 0; j <= radius; ++j)  {
         for (i = -radius; i <= 0; ++i)  {
             c = texture2D(inputImageTexture, uv + vec2(i,j) * src_size).rgb;
             m3 += c;
             s3 += c * c;
         }
     }


     float min_sigma2 = 1e+2;
     m0 /= n;
     s0 = abs(s0 / n - m0 * m0);

     float sigma2 = s0.r + s0.g + s0.b;
     if (sigma2 < min_sigma2) {
         min_sigma2 = sigma2;
         gl_FragColor = vec4(m0, 1.0);
     }

     m1 /= n;
     s1 = abs(s1 / n - m1 * m1);

     sigma2 = s1.r + s1.g + s1.b;
     if (sigma2 < min_sigma2) {
         min_sigma2 = sigma2;
         gl_FragColor = vec4(m1, 1.0);
     }

     m2 /= n;
     s2 = abs(s2 / n - m2 * m2);

     sigma2 = s2.r + s2.g + s2.b;
     if (sigma2 < min_sigma2) {
         min_sigma2 = sigma2;
         gl_FragColor = vec4(m2, 1.0);
     }

     m3 /= n;
     s3 = abs(s3 / n - m3 * m3);

     sigma2 = s3.r + s3.g + s3.b;
     if (sigma2 < min_sigma2) {
         min_sigma2 = sigma2;
         gl_FragColor = vec4(m3, 1.0);
     }
 }
);
#else
NSString *const kGPUImageKuwaharaFragmentShaderString = SHADER_STRING
(
 varying vec2 textureCoordinate;
 uniform sampler2D inputImageTexture;
 uniform int radius;
 
 const vec2 src_size = vec2 (1.0 / 768.0, 1.0 / 1024.0);
 
 void main (void)
 {
     vec2 uv = textureCoordinate;
     float n = float((radius + 1) * (radius + 1));
     int i; int j;
     vec3 m0 = vec3(0.0); vec3 m1 = vec3(0.0); vec3 m2 = vec3(0.0); vec3 m3 = vec3(0.0);
     vec3 s0 = vec3(0.0); vec3 s1 = vec3(0.0); vec3 s2 = vec3(0.0); vec3 s3 = vec3(0.0);
     vec3 c;
     
     for (j = -radius; j <= 0; ++j)  {
         for (i = -radius; i <= 0; ++i)  {
             c = texture2D(inputImageTexture, uv + vec2(i,j) * src_size).rgb;
             m0 += c;
             s0 += c * c;
         }
     }
     
     for (j = -radius; j <= 0; ++j)  {
         for (i = 0; i <= radius; ++i)  {
             c = texture2D(inputImageTexture, uv + vec2(i,j) * src_size).rgb;
             m1 += c;
             s1 += c * c;
         }
     }
     
     for (j = 0; j <= radius; ++j)  {
         for (i = 0; i <= radius; ++i)  {
             c = texture2D(inputImageTexture, uv + vec2(i,j) * src_size).rgb;
             m2 += c;
             s2 += c * c;
         }
     }
     
     for (j = 0; j <= radius; ++j)  {
         for (i = -radius; i <= 0; ++i)  {
             c = texture2D(inputImageTexture, uv + vec2(i,j) * src_size).rgb;
             m3 += c;
             s3 += c * c;
         }
     }
     
     
     float min_sigma2 = 1e+2;
     m0 /= n;
     s0 = abs(s0 / n - m0 * m0);
     
     float sigma2 = s0.r + s0.g + s0.b;
     if (sigma2 < min_sigma2) {
         min_sigma2 = sigma2;
         gl_FragColor = vec4(m0, 1.0);
     }
     
     m1 /= n;
     s1 = abs(s1 / n - m1 * m1);
     
     sigma2 = s1.r + s1.g + s1.b;
     if (sigma2 < min_sigma2) {
         min_sigma2 = sigma2;
         gl_FragColor = vec4(m1, 1.0);
     }
     
     m2 /= n;
     s2 = abs(s2 / n - m2 * m2);
     
     sigma2 = s2.r + s2.g + s2.b;
     if (sigma2 < min_sigma2) {
         min_sigma2 = sigma2;
         gl_FragColor = vec4(m2, 1.0);
     }
     
     m3 /= n;
     s3 = abs(s3 / n - m3 * m3);
     
     sigma2 = s3.r + s3.g + s3.b;
     if (sigma2 < min_sigma2) {
         min_sigma2 = sigma2;
         gl_FragColor = vec4(m3, 1.0);
     }
 }
);
#endif

@implementation GPUImageKuwaharaFilter

@synthesize radius = _radius;

#pragma mark -
#pragma mark Initialization and teardown

- (id)init;
{
    if (!(self = [super initWithFragmentShaderFromString:kGPUImageKuwaharaFragmentShaderString]))
    {
		return nil;
    }
    
    radiusUniform = [filterProgram uniformIndex:@"radius"];

    self.radius = 3;
    
    return self;
}

#pragma mark -
#pragma mark Accessors

- (void)setRadius:(NSUInteger)newValue;
{
    _radius = newValue;
    
    [self setInteger:(GLint)_radius forUniform:radiusUniform program:filterProgram];
}

@end
