// Convolution 
// Daniel Shiffman <http://www.shiffman.net> 

PImage img; 
int w = 80; 
 
void setup() { 
  size(200, 200); 
  framerate(30); 
  img = loadImage("end.jpg"); 
} 
 
void draw() { 
  // We're only going to process a portion of the image 
  // so let's set the whole image as the background first 
  image(img,0,0); 
  // Where is the small rectangle we will process 
  int xstart = constrain(mouseX-w/2,0,img.width); 
  int ystart = constrain(mouseY-w/2,0,img.height); 
  int xend = constrain(mouseX+w/2,0,img.width); 
  int yend = constrain(mouseY+w/2,0,img.height); 
  int matrixsize = 3; 
  // It's possible to convolve the image with 
  // many different matrices 
  /* 
  float[][] matrix = { { -1, -1, -1 }, 
                       { -1,  9, -1 }, 
                       { -1, -1, -1 } }; 
  */ 
  float[][] matrix = { { -2, -2, -2 }, 
                       { -2,  9,  0 }, 
                       { -1,  0,  0 } }; 
  loadPixels(); 
  // Begin our loop for every pixel 
  for (int x = xstart; x < xend; x++) { 
    for (int y = ystart; y < yend; y++ ) { 
      color c = convolution(x,y,matrix,matrixsize,img); 
      int loc = x + y*img.width; 
      pixels[loc] = c; 
    } 
  } 
  updatePixels(); 
} 
 
color convolution(int x, int y, float[][] matrix,int matrixsize, PImage img) 
{ 
  float rtotal = 0.0; 
  float gtotal = 0.0; 
  float btotal = 0.0; 
  int offset = matrixsize / 2; 
  for (int i = 0; i < matrixsize; i++){ 
    for (int j= 0; j < matrixsize; j++){ 
      // What pixel are we testing 
      int xloc = x+i-offset; 
      int yloc = y+j-offset; 
      int loc = xloc + img.width*yloc; 
      // Make sure we haven't walked off our image, we could do better here 
      loc = constrain(loc,0,img.pixels.length-1); 
      // Calculate the convolution 
      rtotal += (red(img.pixels[loc]) * matrix[i][j]); 
      gtotal += (green(img.pixels[loc]) * matrix[i][j]); 
      btotal += (blue(img.pixels[loc]) * matrix[i][j]); 
    } 
  } 
  // Make sure RGB is within range 
  rtotal = constrain(rtotal,0,255); 
  gtotal = constrain(gtotal,0,255); 
  btotal = constrain(btotal,0,255); 
  // Return the resulting color 
  return color(rtotal,gtotal,btotal); 
}