Hi,

I am trying to simulate how particles behave in a sound wave.

I have a random array of dots which oscillate horizontally. But I'd like the oscillation of each to only begin when their x-coordinate is the same as that of a red dot which travels horizontally across the screen.

The code for the dots all oscillating together is,

1. int numDots = 10;
2. float x, angle, frequency = PI;
3. float xpos;
4. float vel = 0.1;
5. int[]ArrayX = new int[numDots];
6. int[]ArrayY = new int[numDots];
7. void setup() {
8.   size (600, 300);
9.   for (int i = 0; i < numDots; i++) {
10.     ArrayX[i] = (int) random(0, width); 
11.     ArrayY[i] = (int) random(0, height);
12.   }
13. }
14. void draw() {
15.   background (127);
16.   stroke(0);
17.   fill(0);                      
18.   for (int i = 0; i < numDots; i++) {
19.     x = sin(radians(angle))*50;
20.     ellipse(ArrayX[i]+x, ArrayY[i], 3, 3);
21.     angle -= frequency/32;
22.     noStroke();
23.     fill(250, 0, 0);
24.     ellipse(xpos, 100, 5, 5);
25.     stroke(0);
26.     fill(0);
27.     xpos += vel;
28.   }
29. }

and to try to get them to only oscillate when the red dot passes using the 'if' statement on line 20:

1. int numDots = 10;
2. float x, angle, frequency = PI;
3. float xpos;
4. float vel = 0.1;
5. int[]ArrayX = new int[numDots];
6. int[]ArrayY = new int[numDots];
7. void setup() {
8.   size (600, 300);
9.   for (int i = 0; i < numDots; i++) {
10.     ArrayX[i] = (int) random(0, width); 
11.     ArrayY[i] = (int) random(0, height);
12.   }
13. }
14. void draw() {
15.   background (127);
16.   stroke(0);
17.   fill(0);                      
18.   for (int i = 0; i < numDots; i++) {
19.     angle -= frequency/32;
20.     if (xpos==ArrayX[i]) {
21.       x = sin(radians(angle))*50;
22.       ellipse(ArrayX[i]+x, ArrayY[i], 3, 3);
23.     }
24.     noStroke();
25.     fill(250, 0, 0);
26.     ellipse(xpos, 100, 5, 5);
27.     stroke(0);
28.     fill(0);
29.     xpos += vel;
30.   }
31. }

 
I don't know why the array of dots can't be seen in the second code.

I'd really appreicate any help.

Thanks,

Shane