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

@implementation GPUImageDirectionalSobelEdgeDetectionFilter

#if TARGET_IPHONE_SIMULATOR || TARGET_OS_IPHONE
NSString *const kGPUImageDirectionalSobelEdgeDetectionFragmentShaderString = SHADER_STRING
(
 precision mediump 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;
 
 void main()
 {
     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;
     
     vec2 gradientDirection;
     gradientDirection.x = -bottomLeftIntensity - 2.0 * leftIntensity - topLeftIntensity + bottomRightIntensity + 2.0 * rightIntensity + topRightIntensity;
     gradientDirection.y = -topLeftIntensity - 2.0 * topIntensity - topRightIntensity + bottomLeftIntensity + 2.0 * bottomIntensity + bottomRightIntensity;
     
     float gradientMagnitude = length(gradientDirection);
     vec2 normalizedDirection = normalize(gradientDirection);
     normalizedDirection = sign(normalizedDirection) * floor(abs(normalizedDirection) + 0.617316); // Offset by 1-sin(pi/8) to set to 0 if near axis, 1 if away
     normalizedDirection = (normalizedDirection + 1.0) * 0.5; // Place -1.0 - 1.0 within 0 - 1.0
     
     gl_FragColor = vec4(gradientMagnitude, normalizedDirection.x, normalizedDirection.y, 1.0);
 }
);
#else
NSString *const kGPUImageDirectionalSobelEdgeDetectionFragmentShaderString = 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;
 
 void main()
 {
     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;
     
     vec2 gradientDirection;
     gradientDirection.x = -bottomLeftIntensity - 2.0 * leftIntensity - topLeftIntensity + bottomRightIntensity + 2.0 * rightIntensity + topRightIntensity;
     gradientDirection.y = -topLeftIntensity - 2.0 * topIntensity - topRightIntensity + bottomLeftIntensity + 2.0 * bottomIntensity + bottomRightIntensity;
     
     float gradientMagnitude = length(gradientDirection);
     vec2 normalizedDirection = normalize(gradientDirection);
     normalizedDirection = sign(normalizedDirection) * floor(abs(normalizedDirection) + 0.617316); // Offset by 1-sin(pi/8) to set to 0 if near axis, 1 if away
     normalizedDirection = (normalizedDirection + 1.0) * 0.5; // Place -1.0 - 1.0 within 0 - 1.0
     
     gl_FragColor = vec4(gradientMagnitude, normalizedDirection.x, normalizedDirection.y, 1.0);
 }
);
#endif

#pragma mark -
#pragma mark Initialization and teardown

- (id)init;
{
    if (!(self = [super initWithFragmentShaderFromString:kGPUImageDirectionalSobelEdgeDetectionFragmentShaderString]))
    {
        return nil;
    }

    return self;
}


@end
