Pods/GPUImage/framework/Source/GPUImageLaplacianFilter.m
#import "GPUImageLaplacianFilter.h"
#if TARGET_IPHONE_SIMULATOR || TARGET_OS_IPHONE
NSString *const kGPUImageLaplacianFragmentShaderString = SHADER_STRING
(
 precision highp float;
 
 uniform sampler2D inputImageTexture;
 
 uniform mediump mat3 convolutionMatrix;
 
 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;
 
 void main()
 {
     mediump vec3 bottomColor = texture2D(inputImageTexture, bottomTextureCoordinate).rgb;
     mediump vec3 bottomLeftColor = texture2D(inputImageTexture, bottomLeftTextureCoordinate).rgb;
     mediump vec3 bottomRightColor = texture2D(inputImageTexture, bottomRightTextureCoordinate).rgb;
     mediump vec4 centerColor = texture2D(inputImageTexture, textureCoordinate);
     mediump vec3 leftColor = texture2D(inputImageTexture, leftTextureCoordinate).rgb;
     mediump vec3 rightColor = texture2D(inputImageTexture, rightTextureCoordinate).rgb;
     mediump vec3 topColor = texture2D(inputImageTexture, topTextureCoordinate).rgb;
     mediump vec3 topRightColor = texture2D(inputImageTexture, topRightTextureCoordinate).rgb;
     mediump vec3 topLeftColor = texture2D(inputImageTexture, topLeftTextureCoordinate).rgb;
     
     mediump vec3 resultColor = topLeftColor * convolutionMatrix[0][0] + topColor * convolutionMatrix[0][1] + topRightColor * convolutionMatrix[0][2];
     resultColor += leftColor * convolutionMatrix[1][0] + centerColor.rgb * convolutionMatrix[1][1] + rightColor * convolutionMatrix[1][2];
     resultColor += bottomLeftColor * convolutionMatrix[2][0] + bottomColor * convolutionMatrix[2][1] + bottomRightColor * convolutionMatrix[2][2];
     
     // Normalize the results to allow for negative gradients in the 0.0-1.0 colorspace
     resultColor = resultColor + 0.5;
     
     gl_FragColor = vec4(resultColor, centerColor.a);
 }
);
#else
NSString *const kGPUImageLaplacianFragmentShaderString = SHADER_STRING
(
 uniform sampler2D inputImageTexture;
 
 uniform mat3 convolutionMatrix;
 
 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;
 
 void main()
 {
     vec3 bottomColor = texture2D(inputImageTexture, bottomTextureCoordinate).rgb;
     vec3 bottomLeftColor = texture2D(inputImageTexture, bottomLeftTextureCoordinate).rgb;
     vec3 bottomRightColor = texture2D(inputImageTexture, bottomRightTextureCoordinate).rgb;
     vec4 centerColor = texture2D(inputImageTexture, textureCoordinate);
     vec3 leftColor = texture2D(inputImageTexture, leftTextureCoordinate).rgb;
     vec3 rightColor = texture2D(inputImageTexture, rightTextureCoordinate).rgb;
     vec3 topColor = texture2D(inputImageTexture, topTextureCoordinate).rgb;
     vec3 topRightColor = texture2D(inputImageTexture, topRightTextureCoordinate).rgb;
     vec3 topLeftColor = texture2D(inputImageTexture, topLeftTextureCoordinate).rgb;
     
     vec3 resultColor = topLeftColor * convolutionMatrix[0][0] + topColor * convolutionMatrix[0][1] + topRightColor * convolutionMatrix[0][2];
     resultColor += leftColor * convolutionMatrix[1][0] + centerColor.rgb * convolutionMatrix[1][1] + rightColor * convolutionMatrix[1][2];
     resultColor += bottomLeftColor * convolutionMatrix[2][0] + bottomColor * convolutionMatrix[2][1] + bottomRightColor * convolutionMatrix[2][2];
     
     // Normalize the results to allow for negative gradients in the 0.0-1.0 colorspace
     resultColor = resultColor + 0.5;

     gl_FragColor = vec4(resultColor, centerColor.a);
 }
);
#endif

@implementation GPUImageLaplacianFilter

- (id)init;
{
    if (!(self = [super initWithFragmentShaderFromString:kGPUImageLaplacianFragmentShaderString]))
    {
		return nil;
    }
    
    GPUMatrix3x3 newConvolutionMatrix;
    newConvolutionMatrix.one.one = 0.5;
    newConvolutionMatrix.one.two = 1.0;
    newConvolutionMatrix.one.three = 0.5;
    
    newConvolutionMatrix.two.one = 1.0;
    newConvolutionMatrix.two.two = -6.0;
    newConvolutionMatrix.two.three = 1.0;
    
    newConvolutionMatrix.three.one = 0.5;
    newConvolutionMatrix.three.two = 1.0;
    newConvolutionMatrix.three.three = 0.5;
    
    self.convolutionKernel = newConvolutionMatrix;
    
    return self;
}

@end
