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

#import "GPUImageGrayscaleFilter.h"
#import "GPUImage3x3TextureSamplingFilter.h"
#import "GPUImageNonMaximumSuppressionFilter.h"

// 14 total texture coordinates from vertex shader for non-dependent reads
// 3 texture coordinates for dependent reads, then

NSString *const kGPUImageFASTDetectorFragmentShaderString = 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 sampler2D lookupTable;
 
 void main()
 {
     lowp float centerIntensity = texture2D(inputImageTexture, textureCoordinate).r;
     lowp float bottomLeftIntensity = texture2D(inputImageTexture, bottomLeftTextureCoordinate).r;
     lowp float topRightIntensity = texture2D(inputImageTexture, topRightTextureCoordinate).r;
     lowp float topLeftIntensity = texture2D(inputImageTexture, topLeftTextureCoordinate).r;
     lowp float bottomRightIntensity = texture2D(inputImageTexture, bottomRightTextureCoordinate).r;
     lowp float leftIntensity = texture2D(inputImageTexture, leftTextureCoordinate).r;
     lowp float rightIntensity = texture2D(inputImageTexture, rightTextureCoordinate).r;
     lowp float bottomIntensity = texture2D(inputImageTexture, bottomTextureCoordinate).r;
     lowp float topIntensity = texture2D(inputImageTexture, topTextureCoordinate).r;
     
     lowp float byteTally = 1.0 / 255.0 * step(centerIntensity, topRightIntensity);
     byteTally += 2.0 / 255.0 * step(centerIntensity, topIntensity);
     byteTally += 4.0 / 255.0 * step(centerIntensity, topLeftIntensity);
     byteTally += 8.0 / 255.0 * step(centerIntensity, leftIntensity);
     byteTally += 16.0 / 255.0 * step(centerIntensity, bottomLeftIntensity);
     byteTally += 32.0 / 255.0 * step(centerIntensity, bottomIntensity);
     byteTally += 64.0 / 255.0 * step(centerIntensity, bottomRightIntensity);
     byteTally += 128.0 / 255.0 * step(centerIntensity, rightIntensity);
     
     // TODO: Replace the above with a dot product and two vec4s
     // TODO: Apply step to a matrix, rather than individually
     
     gl_FragColor = vec4(byteTally, byteTally, byteTally, 1.0);
 }
 );


@implementation GPUImageFASTCornerDetectionFilter

- (id)init;
{
    if (!(self = [self initWithFASTDetectorVariant:kGPUImageFAST12ContiguousNonMaximumSuppressed]))
    {
        return nil;
    }
    
    return self;
}

- (id)initWithFASTDetectorVariant:(GPUImageFASTDetectorType)detectorType;
{
    if (!(self = [super init]))
    {
		return nil;
    }
    
//    [derivativeFilter addTarget:blurFilter];
//    [blurFilter addTarget:harrisCornerDetectionFilter];
//    [harrisCornerDetectionFilter addTarget:nonMaximumSuppressionFilter];
    //    [simpleThresholdFilter addTarget:colorPackingFilter];
    
//    self.initialFilters = [NSArray arrayWithObjects:derivativeFilter, nil];
    //    self.terminalFilter = colorPackingFilter;
//    self.terminalFilter = nonMaximumSuppressionFilter;

    return self;
}

@end
