framework/Source/GPUImageToonFilter.m
#import "GPUImageToonFilter.h"
#import "GPUImageSobelEdgeDetectionFilter.h"
#import "GPUImage3x3ConvolutionFilter.h"

// Code from "Graphics Shaders: Theory and Practice" by M. Bailey and S. Cunningham 
#if TARGET_IPHONE_SIMULATOR || TARGET_OS_IPHONE
NSString *const kGPUImageToonFragmentShaderString = SHADER_STRING
(
 precision highp float;
 
 varying vec2 textureCoordinate;
 varying vec2 leftTextureCoordinate;
 varying vec2 rightTextureCoordinate;
 
 varying vec2 topTextureCoordinate;
 varying vec2 topLeftTextureCoordinate;
 varying vec2 topRightTextureCoordinate;
 
 varying vec2 bottomTextureCoordinate;
 varying vec2 bottomLeftTextureCoordinate;
 varying vec2 bottomRightTextureCoordinate;
 
 uniform sampler2D inputImageTexture;
 
 uniform highp float intensity;
 uniform highp float threshold;
 uniform highp float quantizationLevels;
 
 const highp vec3 W = vec3(0.2125, 0.7154, 0.0721);
 
 void main()
 {
     vec4 textureColor = texture2D(inputImageTexture, textureCoordinate);
     
     float bottomLeftIntensity = texture2D(inputImageTexture, bottomLeftTextureCoordinate).r;
     float topRightIntensity = texture2D(inputImageTexture, topRightTextureCoordinate).r;
     float topLeftIntensity = texture2D(inputImageTexture, topLeftTextureCoordinate).r;
     float bottomRightIntensity = texture2D(inputImageTexture, bottomRightTextureCoordinate).r;
     float leftIntensity = texture2D(inputImageTexture, leftTextureCoordinate).r;
     float rightIntensity = texture2D(inputImageTexture, rightTextureCoordinate).r;
     float bottomIntensity = texture2D(inputImageTexture, bottomTextureCoordinate).r;
     float topIntensity = texture2D(inputImageTexture, topTextureCoordinate).r;
     float h = -topLeftIntensity - 2.0 * topIntensity - topRightIntensity + bottomLeftIntensity + 2.0 * bottomIntensity + bottomRightIntensity;
     float v = -bottomLeftIntensity - 2.0 * leftIntensity - topLeftIntensity + bottomRightIntensity + 2.0 * rightIntensity + topRightIntensity;
     
     float mag = length(vec2(h, v));

     vec3 posterizedImageColor = floor((textureColor.rgb * quantizationLevels) + 0.5) / quantizationLevels;
     
     float thresholdTest = 1.0 - step(threshold, mag);
     
     gl_FragColor = vec4(posterizedImageColor * thresholdTest, textureColor.a);
 }
);
#else
NSString *const kGPUImageToonFragmentShaderString = SHADER_STRING
(
 varying vec2 textureCoordinate;
 varying vec2 leftTextureCoordinate;
 varying vec2 rightTextureCoordinate;
 
 varying vec2 topTextureCoordinate;
 varying vec2 topLeftTextureCoordinate;
 varying vec2 topRightTextureCoordinate;
 
 varying vec2 bottomTextureCoordinate;
 varying vec2 bottomLeftTextureCoordinate;
 varying vec2 bottomRightTextureCoordinate;
 
 uniform sampler2D inputImageTexture;
 
 uniform float intensity;
 uniform float threshold;
 uniform float quantizationLevels;
 
 const vec3 W = vec3(0.2125, 0.7154, 0.0721);
 
 void main()
 {
     vec4 textureColor = texture2D(inputImageTexture, textureCoordinate);
     
     float bottomLeftIntensity = texture2D(inputImageTexture, bottomLeftTextureCoordinate).r;
     float topRightIntensity = texture2D(inputImageTexture, topRightTextureCoordinate).r;
     float topLeftIntensity = texture2D(inputImageTexture, topLeftTextureCoordinate).r;
     float bottomRightIntensity = texture2D(inputImageTexture, bottomRightTextureCoordinate).r;
     float leftIntensity = texture2D(inputImageTexture, leftTextureCoordinate).r;
     float rightIntensity = texture2D(inputImageTexture, rightTextureCoordinate).r;
     float bottomIntensity = texture2D(inputImageTexture, bottomTextureCoordinate).r;
     float topIntensity = texture2D(inputImageTexture, topTextureCoordinate).r;
     float h = -topLeftIntensity - 2.0 * topIntensity - topRightIntensity + bottomLeftIntensity + 2.0 * bottomIntensity + bottomRightIntensity;
     float v = -bottomLeftIntensity - 2.0 * leftIntensity - topLeftIntensity + bottomRightIntensity + 2.0 * rightIntensity + topRightIntensity;
     
     float mag = length(vec2(h, v));
     
     vec3 posterizedImageColor = floor((textureColor.rgb * quantizationLevels) + 0.5) / quantizationLevels;
     
     float thresholdTest = 1.0 - step(threshold, mag);
     
     gl_FragColor = vec4(posterizedImageColor * thresholdTest, textureColor.a);
 }
);
#endif

@implementation GPUImageToonFilter

@synthesize threshold = _threshold; 
@synthesize quantizationLevels = _quantizationLevels; 

#pragma mark -
#pragma mark Initialization and teardown

- (id)init;
{
    if (!(self = [super initWithFragmentShaderFromString:kGPUImageToonFragmentShaderString]))
    {
		return nil;
    }
    
    hasOverriddenImageSizeFactor = NO;
    
    thresholdUniform = [filterProgram uniformIndex:@"threshold"];
    quantizationLevelsUniform = [filterProgram uniformIndex:@"quantizationLevels"];
    
    self.threshold = 0.2;
    self.quantizationLevels = 10.0;    

    return self;
}

#pragma mark -
#pragma mark Accessors

- (void)setThreshold:(CGFloat)newValue;
{
    _threshold = newValue;
    
    [self setFloat:_threshold forUniform:thresholdUniform program:filterProgram];
}

- (void)setQuantizationLevels:(CGFloat)newValue;
{
    _quantizationLevels = newValue;
    
    [self setFloat:_quantizationLevels forUniform:quantizationLevelsUniform program:filterProgram];
}


@end

