Chapter 16: Video: Exercise 16-5: Color Tracking with Snake

// Learning Processing
// Daniel Shiffman
// http://www.learningprocessing.com

// Exercise 16-5: Take any Processing sketch you previously created that involves mouse interaction and 
// replace the mouse with color tracking. Create an environment for the camera that is simple and high contrast. 
// For example, point the camera at a black tabletop with a small white object. 
// Control your sketch with the object's location. 

import processing.video.*;

// Variable for capture device
Capture video;

// A variable for the color we are searching for.
color trackColor; 

// A Snake variable
Snake snake;

void setup() {
  size(320,240);
  video = new Capture(this,width,height,15);
  // Start off tracking for red
  trackColor = color(255,0,0);
  smooth();
  
  // Initialize the snake
  snake = new Snake(50);
  
}

void draw() {
  // Capture and display the video
  if (video.available()) {
    video.read();
  }
  
  video.loadPixels();
  image(video,0,0);

  // Before we begin searching, the "world record" for closest color is set to a high number that is easy for the first pixel to beat.
  float worldRecord = 500; 

  // XY coordinate of closest color
  int closestX = 0;
  int closestY = 0;

  // Begin loop to walk through every pixel
  for (int x = 0; x < video.width; x ++ ) {
    for (int y = 0; y < video.height; y ++ ) {
      int loc = x + y*video.width;
      // What is current color
      color currentColor = video.pixels[loc];
      float r1 = red(currentColor);
      float g1 = green(currentColor);
      float b1 = blue(currentColor);
      float r2 = red(trackColor);
      float g2 = green(trackColor);
      float b2 = blue(trackColor);

      // Using euclidean distance to compare colors
      float d = dist(r1,g1,b1,r2,g2,b2); // We are using the dist( ) function to compare the current color with the color we are tracking.

      // If current color is more similar to tracked color than
      // closest color, save current location and current difference
      if (d < worldRecord) {
        worldRecord = d;
        closestX = x;
        closestY = y;
      }
    }
  }

  // We only consider the color found if its color distance is less than 10. 
  // This threshold of 10 is arbitrary and you can adjust this number depending on how accurate you require the tracking to be.
  if (worldRecord < 10) { 
    // Update the snake's location
    snake.update(closestX,closestY);
  }
  
  snake.display();
  
}

void mousePressed() {
  // Save color where the mouse is clicked in trackColor variable
    saveFrame("blah.tif");
  int loc = mouseX + mouseY*video.width;
  trackColor = video.pixels[loc];

}

// Learning Processing
// Daniel Shiffman
// http://www.learningprocessing.com

// Exercise 16-5: Snake Class

class Snake {
  // x and y positions
  int[] xpos;
  int[] ypos;

  // The constructor determines the length of the snake
  Snake(int n) {
    xpos = new int[n];
    ypos = new int[n];
  }

  void update(int newX, int newY) {
    // Shift all elements down one spot. 
    // xpos[0] = xpos[1], xpos[1] = xpos = [2], and so on. Stop at the second to last element.
    for (int i = 0; i < xpos.length-1; i ++ ) {
      xpos[i] = xpos[i+1]; 
      ypos[i] = ypos[i+1];
    }

    // Update the last spot in the array with the mouse location.
    xpos[xpos.length-1] = newX; 
    ypos[ypos.length-1] = newY;
  }

  void display() {
    // Draw everything
    for (int i = 0; i < xpos.length; i ++ ) {
      // Draw an ellipse for each element in the arrays. 
      // Color and size are tied to the loop's counter: i.
      stroke(0);
      fill(255-i*5);
      ellipse(xpos[i],ypos[i],i,i); 
    }

  }

}