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

#if TARGET_IPHONE_SIMULATOR || TARGET_OS_IPHONE
NSString *const kGPUImageThresholdedNonMaximumSuppressionFragmentShaderString = SHADER_STRING
(
 uniform sampler2D inputImageTexture;
 
 varying highp vec2 textureCoordinate;
 varying highp vec2 leftTextureCoordinate;
 varying highp vec2 rightTextureCoordinate;
 
 varying highp vec2 topTextureCoordinate;
 varying highp vec2 topLeftTextureCoordinate;
 varying highp vec2 topRightTextureCoordinate;
 
 varying highp vec2 bottomTextureCoordinate;
 varying highp vec2 bottomLeftTextureCoordinate;
 varying highp vec2 bottomRightTextureCoordinate;
 
 uniform lowp float threshold;
 
 void main()
 {
     lowp float bottomColor = texture2D(inputImageTexture, bottomTextureCoordinate).r;
     lowp float bottomLeftColor = texture2D(inputImageTexture, bottomLeftTextureCoordinate).r;
     lowp float bottomRightColor = texture2D(inputImageTexture, bottomRightTextureCoordinate).r;
     lowp vec4 centerColor = texture2D(inputImageTexture, textureCoordinate);
     lowp float leftColor = texture2D(inputImageTexture, leftTextureCoordinate).r;
     lowp float rightColor = texture2D(inputImageTexture, rightTextureCoordinate).r;
     lowp float topColor = texture2D(inputImageTexture, topTextureCoordinate).r;
     lowp float topRightColor = texture2D(inputImageTexture, topRightTextureCoordinate).r;
     lowp float topLeftColor = texture2D(inputImageTexture, topLeftTextureCoordinate).r;
     
     // Use a tiebreaker for pixels to the left and immediately above this one
     lowp float multiplier = 1.0 - step(centerColor.r, topColor);
     multiplier = multiplier * (1.0 - step(centerColor.r, topLeftColor));
     multiplier = multiplier * (1.0 - step(centerColor.r, leftColor));
     multiplier = multiplier * (1.0 - step(centerColor.r, bottomLeftColor));
     
     lowp float maxValue = max(centerColor.r, bottomColor);
     maxValue = max(maxValue, bottomRightColor);
     maxValue = max(maxValue, rightColor);
     maxValue = max(maxValue, topRightColor);
     
     lowp float finalValue = centerColor.r * step(maxValue, centerColor.r) * multiplier;
     finalValue = step(threshold, finalValue);
     
     gl_FragColor = vec4(finalValue, finalValue, finalValue, 1.0);
//
//     gl_FragColor = vec4((centerColor.rgb * step(maxValue, step(threshold, centerColor.r)) * multiplier), 1.0);
 }
);

NSString *const kGPUImageThresholdedNonMaximumSuppressionPackedColorspaceFragmentShaderString = SHADER_STRING
(
 uniform sampler2D inputImageTexture;
 
 varying highp vec2 textureCoordinate;
 varying highp vec2 leftTextureCoordinate;
 varying highp vec2 rightTextureCoordinate;
 
 varying highp vec2 topTextureCoordinate;
 varying highp vec2 topLeftTextureCoordinate;
 varying highp vec2 topRightTextureCoordinate;
 
 varying highp vec2 bottomTextureCoordinate;
 varying highp vec2 bottomLeftTextureCoordinate;
 varying highp vec2 bottomRightTextureCoordinate;
 
 uniform lowp float threshold;
 uniform highp float texelWidth;
 uniform highp float texelHeight;

 highp float encodedIntensity(highp vec3 sourceColor)
 {
     return (sourceColor.b * 256.0 * 256.0 + sourceColor.g * 256.0 + sourceColor.r);
 }
 
 void main()
 {
     highp float bottomColor = encodedIntensity(texture2D(inputImageTexture, bottomTextureCoordinate).rgb);
     highp float bottomLeftColor = encodedIntensity(texture2D(inputImageTexture, bottomLeftTextureCoordinate).rgb);
     highp float bottomRightColor = encodedIntensity(texture2D(inputImageTexture, bottomRightTextureCoordinate).rgb);
     highp float centerColor = encodedIntensity(texture2D(inputImageTexture, textureCoordinate).rgb);
     highp float leftColor = encodedIntensity(texture2D(inputImageTexture, leftTextureCoordinate).rgb);
     highp float rightColor = encodedIntensity(texture2D(inputImageTexture, rightTextureCoordinate).rgb);
     highp float topColor = encodedIntensity(texture2D(inputImageTexture, topTextureCoordinate).rgb);
     highp float topRightColor = encodedIntensity(texture2D(inputImageTexture, topRightTextureCoordinate).rgb);
     highp float topLeftColor = encodedIntensity(texture2D(inputImageTexture, topLeftTextureCoordinate).rgb);
     
     highp float secondStageColor1 = encodedIntensity(texture2D(inputImageTexture, textureCoordinate + vec2(-2.0 * texelWidth, -2.0 * texelHeight)).rgb);
     highp float secondStageColor2 = encodedIntensity(texture2D(inputImageTexture, textureCoordinate + vec2(-2.0 * texelWidth, -1.0 * texelHeight)).rgb);
     highp float secondStageColor3 = encodedIntensity(texture2D(inputImageTexture, textureCoordinate + vec2(-2.0 * texelWidth, 0.0)).rgb);
     highp float secondStageColor4 = encodedIntensity(texture2D(inputImageTexture, textureCoordinate + vec2(-2.0 * texelWidth, 1.0 * texelHeight)).rgb);
     highp float secondStageColor5 = encodedIntensity(texture2D(inputImageTexture, textureCoordinate + vec2(-2.0 * texelWidth, 2.0 * texelHeight)).rgb);
     highp float secondStageColor6 = encodedIntensity(texture2D(inputImageTexture, textureCoordinate + vec2(-1.0 * texelWidth, 2.0 * texelHeight)).rgb);
     highp float secondStageColor7 = encodedIntensity(texture2D(inputImageTexture, textureCoordinate + vec2(0.0, 2.0 * texelHeight)).rgb);
     highp float secondStageColor8 = encodedIntensity(texture2D(inputImageTexture, textureCoordinate + vec2(1.0 * texelWidth, 2.0 * texelHeight)).rgb);

     highp float thirdStageColor1 = encodedIntensity(texture2D(inputImageTexture, textureCoordinate + vec2(-1.0 * texelWidth, -2.0 * texelHeight)).rgb);
     highp float thirdStageColor2 = encodedIntensity(texture2D(inputImageTexture, textureCoordinate + vec2(0.0, -2.0 * texelHeight)).rgb);
     highp float thirdStageColor3 = encodedIntensity(texture2D(inputImageTexture, textureCoordinate + vec2(1.0 * texelWidth, -2.0 * texelHeight)).rgb);
     highp float thirdStageColor4 = encodedIntensity(texture2D(inputImageTexture, textureCoordinate + vec2(2.0 * texelWidth, -2.0 * texelHeight)).rgb);
     highp float thirdStageColor5 = encodedIntensity(texture2D(inputImageTexture, textureCoordinate + vec2(2.0 * texelWidth, -1.0 * texelHeight)).rgb);
     highp float thirdStageColor6 = encodedIntensity(texture2D(inputImageTexture, textureCoordinate + vec2(2.0 * texelWidth, 0.0)).rgb);
     highp float thirdStageColor7 = encodedIntensity(texture2D(inputImageTexture, textureCoordinate + vec2(2.0 * texelWidth, 1.0 * texelHeight)).rgb);
     highp float thirdStageColor8 = encodedIntensity(texture2D(inputImageTexture, textureCoordinate + vec2(2.0 * texelWidth, 2.0 * texelHeight)).rgb);
     
     // Use a tiebreaker for pixels to the left and immediately above this one
     highp float multiplier = 1.0 - step(centerColor, topColor);
     multiplier = multiplier * (1.0 - step(centerColor, topLeftColor));
     multiplier = multiplier * (1.0 - step(centerColor, leftColor));
     multiplier = multiplier * (1.0 - step(centerColor, bottomLeftColor));

     multiplier = multiplier * (1.0 - step(centerColor, secondStageColor1));
     multiplier = multiplier * (1.0 - step(centerColor, secondStageColor2));
     multiplier = multiplier * (1.0 - step(centerColor, secondStageColor3));
     multiplier = multiplier * (1.0 - step(centerColor, secondStageColor4));
     multiplier = multiplier * (1.0 - step(centerColor, secondStageColor5));
     multiplier = multiplier * (1.0 - step(centerColor, secondStageColor6));
     multiplier = multiplier * (1.0 - step(centerColor, secondStageColor7));
     multiplier = multiplier * (1.0 - step(centerColor, secondStageColor8));

     highp float maxValue = max(centerColor, bottomColor);
     maxValue = max(maxValue, bottomRightColor);
     maxValue = max(maxValue, rightColor);
     maxValue = max(maxValue, topRightColor);

     maxValue = max(maxValue, thirdStageColor1);
     maxValue = max(maxValue, thirdStageColor2);
     maxValue = max(maxValue, thirdStageColor3);
     maxValue = max(maxValue, thirdStageColor4);
     maxValue = max(maxValue, thirdStageColor5);
     maxValue = max(maxValue, thirdStageColor6);
     maxValue = max(maxValue, thirdStageColor7);
     maxValue = max(maxValue, thirdStageColor8);

     highp float midValue = centerColor * step(maxValue, centerColor) * multiplier;
     highp float finalValue = step(threshold, midValue);
     
     gl_FragColor = vec4(finalValue * centerColor, topLeftColor, topRightColor, topColor);
 }
);
#else
NSString *const kGPUImageThresholdedNonMaximumSuppressionFragmentShaderString = SHADER_STRING
(
 uniform sampler2D inputImageTexture;
 
 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 float threshold;
 
 void main()
 {
     float bottomColor = texture2D(inputImageTexture, bottomTextureCoordinate).r;
     float bottomLeftColor = texture2D(inputImageTexture, bottomLeftTextureCoordinate).r;
     float bottomRightColor = texture2D(inputImageTexture, bottomRightTextureCoordinate).r;
     vec4 centerColor = texture2D(inputImageTexture, textureCoordinate);
     float leftColor = texture2D(inputImageTexture, leftTextureCoordinate).r;
     float rightColor = texture2D(inputImageTexture, rightTextureCoordinate).r;
     float topColor = texture2D(inputImageTexture, topTextureCoordinate).r;
     float topRightColor = texture2D(inputImageTexture, topRightTextureCoordinate).r;
     float topLeftColor = texture2D(inputImageTexture, topLeftTextureCoordinate).r;
     
     // Use a tiebreaker for pixels to the left and immediately above this one
     float multiplier = 1.0 - step(centerColor.r, topColor);
     multiplier = multiplier * (1.0 - step(centerColor.r, topLeftColor));
     multiplier = multiplier * (1.0 - step(centerColor.r, leftColor));
     multiplier = multiplier * (1.0 - step(centerColor.r, bottomLeftColor));
     
     float maxValue = max(centerColor.r, bottomColor);
     maxValue = max(maxValue, bottomRightColor);
     maxValue = max(maxValue, rightColor);
     maxValue = max(maxValue, topRightColor);
     
     float finalValue = centerColor.r * step(maxValue, centerColor.r) * multiplier;
     finalValue = step(threshold, finalValue);
     
     gl_FragColor = vec4(finalValue, finalValue, finalValue, 1.0);
     //
     //     gl_FragColor = vec4((centerColor.rgb * step(maxValue, step(threshold, centerColor.r)) * multiplier), 1.0);
 }
);

NSString *const kGPUImageThresholdedNonMaximumSuppressionPackedColorspaceFragmentShaderString = SHADER_STRING
(
 uniform sampler2D inputImageTexture;
 
 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 float threshold;
 
 void main()
 {
     float bottomColor = texture2D(inputImageTexture, bottomTextureCoordinate).r;
     float bottomLeftColor = texture2D(inputImageTexture, bottomLeftTextureCoordinate).r;
     float bottomRightColor = texture2D(inputImageTexture, bottomRightTextureCoordinate).r;
     vec4 centerColor = texture2D(inputImageTexture, textureCoordinate);
     float leftColor = texture2D(inputImageTexture, leftTextureCoordinate).r;
     float rightColor = texture2D(inputImageTexture, rightTextureCoordinate).r;
     float topColor = texture2D(inputImageTexture, topTextureCoordinate).r;
     float topRightColor = texture2D(inputImageTexture, topRightTextureCoordinate).r;
     float topLeftColor = texture2D(inputImageTexture, topLeftTextureCoordinate).r;
     
     // Use a tiebreaker for pixels to the left and immediately above this one
     float multiplier = 1.0 - step(centerColor.r, topColor);
     multiplier = multiplier * (1.0 - step(centerColor.r, topLeftColor));
     multiplier = multiplier * (1.0 - step(centerColor.r, leftColor));
     multiplier = multiplier * (1.0 - step(centerColor.r, bottomLeftColor));
     
     float maxValue = max(centerColor.r, bottomColor);
     maxValue = max(maxValue, bottomRightColor);
     maxValue = max(maxValue, rightColor);
     maxValue = max(maxValue, topRightColor);
     
     float finalValue = centerColor.r * step(maxValue, centerColor.r) * multiplier;
     finalValue = step(threshold, finalValue);
     
     gl_FragColor = vec4(finalValue, finalValue, finalValue, 1.0);
     //
     //     gl_FragColor = vec4((centerColor.rgb * step(maxValue, step(threshold, centerColor.r)) * multiplier), 1.0);
 }
 );
#endif

@implementation GPUImageThresholdedNonMaximumSuppressionFilter

@synthesize threshold = _threshold;

#pragma mark -
#pragma mark Initialization and teardown

- (id)init;
{
    if (!(self = [self initWithPackedColorspace:NO]))
    {
        return nil;
    }
    
    return self;
}

- (id)initWithPackedColorspace:(BOOL)inputUsesPackedColorspace;
{
    NSString *shaderString;
    if (inputUsesPackedColorspace)
    {
        shaderString = kGPUImageThresholdedNonMaximumSuppressionPackedColorspaceFragmentShaderString;
    }
    else
    {
        shaderString = kGPUImageThresholdedNonMaximumSuppressionFragmentShaderString;
    }
    
    
    if (!(self = [super initWithFragmentShaderFromString:shaderString]))
    {
        return nil;
    }
    
    thresholdUniform = [filterProgram uniformIndex:@"threshold"];
    self.threshold = 0.9;
    
    return self;
}

#pragma mark -
#pragma mark Accessors

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

@end
