Creating a list of data and accessing a value

hen

Hi,

I am trying to track and object and determine the difference in angle by subtracting the previous angle from the current. Problem is it is too fast and I often get a value of zero. How can I put the variable 'previousAngle' into a list so that I can, for instance, subtract the previousAngle from 10 readings ago from the current angle.

I am very new to processing so please bear with me if I seem slow.

Many thanks.

GoToLoop

You should start by posting your attempt here. If it's too big, make a model of the part you got problem with!
By your description, a Queue would be the best tool. Java got an ArrayDeque class for it! =:)

hen

Hi,

You helped me identify the need to use array or float in a previous discussion: http://forum.processing.org/two/discussion/593/comparing-current-angle-of-tracked-pixel-to-previous-delay#Item_6 I am struggling to understand how to use either, I have read the reference entries for both and am none the wiser. I basically just need to slow the comparison between current and previous angles.

hen

can Queue only retrieve the head of the queue?

GoToLoop

Yup. a Queue adds to its tail and retrieves from its head! It's a FIFO structure, aka FCFS (1st come, 1st served). (~~)

A kewl demo using it: :ar!

/** 
 * Brownian Motion (v2.26)
 * by Ammon.Owed (2013/Aug)
 * mod GoToLoop
 * 
 * forum.processing.org/topic/
 * controlling-the-length-of-line-from-x-y-to-a-point-which-is-randomly-chosen
 */

import java.util.Queue;
import java.util.ArrayDeque;

final static int DIM = 100, MAX = 03000, DETAIL = 1000, DEPTH = 2000;
final static int HUE = 1<<10, FPS = 60, TOLERANCE = 40, ALIASING = 2;

final static float BOLD = 1.5;
final static boolean HAS_MAX_LIMIT = true;

final Queue<PVector> points = new ArrayDeque(MAX);
final PVector cam = new PVector(), lp = new PVector();

float canvasRatio;

void setup() {
  size(1000, 700, P3D);
  colorMode(HSB, HUE, 1, 1);

  frameRate(FPS);
  smooth(ALIASING);

  strokeWeight(BOLD);
  noFill();

  canvasRatio = (float) width/height;
  frameRate = TOLERANCE<<1;
}

void draw() {
  // auxiliary local variables:
  final int fc = frameCount, fr = round(frameRate);
  final PVector np = new PVector(); // new point.

  // interpolated rotating camera aimed at latest point (tail):
  cam.mult(.99);
  cam.add(PVector.mult(lp, .01, np));

  camera(cam.x + sin(fc*.01)*DETAIL, cam.y + cos(10 + fc*8e-3)*DETAIL, 
  cam.z - DEPTH, cam.x, cam.y, cam.z, 0, 1, 0);

  //perspective(THIRD_PI, canvasRatio, 1, 1e6);

  // draw colored curved lines:
  clear();

  int idx = 0;
  beginShape();

  for (PVector p: points) {
    stroke(fc + idx++ & HUE - 1, 1, 1);
    curveVertex(p.x, p.y, p.z);
  }

  endShape();

  // remove oldest point (head) if limit is reached:
  if (HAS_MAX_LIMIT) {
    if (fc > MAX)        points.remove();
  }

  else
    if (fr < TOLERANCE)  points.remove();

  // generate a new point at specified range:
  PVector.random3D(np, this).mult(DIM); // pick a new random direction.
  np.add(lp);                           // add that up from latest point.
  lp.set(np);                           // this is now the latest point too.

  points.add(np);                       // add new point to queue's tail.

  frame.setTitle("Brownian Motion\t\tFPS: " +fr+ "\t\tSize: " +points.size());
}