I have two ArrayLists in Processing, both of which I need to send to Arduino, and have the Arduino store them in its own arrays

Question

I have the following sketch written in Processing, which scans an image, and stores the coordinates of each black pixel into two ArrayLists - xList, and yList. It currently then prints out the coordinates, but now I need to send these ArrayLists to an Arduino, and have the Arduino store it in its own two arrays (or one 2D array). The problem I'm running into is not being able to tell the Arduino when the data from xList ends, and the data from yList begins, as there isn't a predefined number of elements in the ArrayLists.

import javax.swing.*;

PImage img;
//Threshold determines what is considered a "black" pixel
//based on a 0-255 grayscale.
int threshold = 50;

void setup() {

  // File opener
  try{
    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
  } catch (Exception e) {
    e.printStackTrace();
  }
  final JFileChooser fc = new JFileChooser();

  int returnVal = fc.showOpenDialog(this);

  if (returnVal == JFileChooser.APPROVE_OPTION) {
    File file = fc.getSelectedFile();
    if (file.getName().endsWith("jpg")) {
      img = loadImage(file.getPath());
      if (img != null) {
        size(img.width,img.height);
        image(img,0,0);
      }
    } else {
      println("Please select a .jpg image file.");
    }
  }
  //I added noLoop() here, because the program would output 
  //the coordinates continuously until it was stopped.
  noLoop();
}

void draw() {
  //Here it scans through each pixel of the image.
  ArrayList xList = new ArrayList();
  ArrayList yList = new ArrayList();
  for (int ix = 0; ix < img.width; ix++) {
    for (int iy = 0; iy < img.height; iy++) {
      //If the brightness of the pixel at (ix,iy) is less than
      //the threshold
      if (brightness(get(ix,iy)) < threshold) {
        //Add ix, and iy to their respective ArrayList.
        xList.add(ix);
        yList.add(iy);
      }
    }
  }
  //Print out each coordinate
  //For this statement, I use xList.size() as the limiting
  //condition, because xList and yList should be the same size.
  for (int i=0; i<xList.size(); i++) {
    println("X:" + xList.get(i) + " Y:" + yList.get(i));
  }
}

score 0 · Answer 1 · answered Sep 25 '12 at 17:48

Since both arrays are known to be the same size instead of sending the entire X list and then the entire Y list, you could send one x then one y then the next x then the next y...

On the Arduino side, you would place the first number received into the x array, and then the second into the Y array, the third into the X, fourth into the Y, etc...

One thing to look out for on the Arduino is that since its in C++ there is no bounds checking on arrays, nor do arrays grow when new data is added to them. You'll have to make sure that the arrays are initialized with enough storage to fit all of the coordinates.

I have two ArrayLists in Processing, both of which I need to send to Arduino, and have the Arduino store them in its own arrays

1 Answers1