Drawing a trail for a moving object

Programming Questions

rialobran

Drawing a trail for a moving object

in Programming Questions • 8 months ago

I'm working on an object moving around an attractor (maths mainly based on the GravitationalAttraction3D example).

However, I'd like to have it leave a trail to make it a bit more obvious. The point moves around in the expected fashion, but leaves no trail.

It's been a while since I've tried processing (never really got the hang of arrays the first time!) but this code also looks wrong. Is there anyway I can leave a trail, and make the code more readable?

void display() {
trailx[0] = location.x;
traily[0] = location.y;
for(int i = 0; i < trailx.length-1; i++){
trailx[i+1] = trailx[i];
}
for(int i = 0; i < traily.length-1; i++){
traily[i+1] = traily[i];
}
for(int i = traily.length-1; i > 1; i--){
line(trailx[i], traily[i], trailx[i-1], traily[i-1]);
}
line(location.x, location.y, trailx[0], traily[0]);
}

Replies(3)

quarks

Re: Drawing a trail for a moving object

8 months ago

This could be made a lot clearer if you use a LinkedList and a class to hold the x,y coordinates.

The code below demonstrates this. Click on the diaply and it will show a trail through the last 4 points.

import java.util.*;
LinkedList<PointXY> trail;
int maxTrailLength = 4;
public void setup() {
size(400, 400);
trail = new LinkedList<PointXY>();
stroke(255, 0, 0);
strokeWeight(2);
}
public void mouseClicked() {
// Get the current point and add it to the front of the list
PointXY p = new PointXY(mouseX, mouseY);
trail.addFirst(p);
// If trail is too 'long' remove the oldest points
while (trail.size () > maxTrailLength)
trail.removeLast();
}
public void draw() {
background(255);
// Draw trail if there are at least 2 points
if (trail.size() >= 2) {
PointXY currPoint, lastPoint = trail.get(0);
for (int i = 0; i < trail.size(); i++) {
currPoint = trail.get(i);
line(lastPoint.x, lastPoint.y, currPoint.x, currPoint.y);
lastPoint = currPoint;
}
}
}
public class PointXY {
public float x, y;
public PointXY(float px, float py) {
x = px;
y = py;
}
}

rialobran

Re: Drawing a trail for a moving object

8 months ago

Fantastic. Thanks!

Looks like I've got some reading to do to understand it though. Is there anywhere (related to processing) I can use to learn about linked lists?

GoToLoop

Re: Drawing a trail for a moving object

8 months ago

Hey! I did some experiments on my own on more obscure collection lists.
I've modded quarks' version to use an ArrayDeque instead!
Check it out:

/**
 * Trailing Deque (v3.2)
 * by  quarks (2013/Feb)
 * for rialobran
 * mod GoToLoop
 *
 * http://forum.processing.org/topic/drawing-a-trail-for-a-moving-object
 */

//import java.util.*;

final static byte maxTrailPoints = 5;
final static Queue
               
                 trails = 
                new ArrayDeque(maxTrailPoints);
PointXY tt;


                byte currTrailSize;

                boolean isFull, trailOrLinked;


                void 
                setup() {
  
                size(800, 600);
  
                frameRate(100);
  
                smooth();

  
                keyPressed();

  
                stroke(#0000FF);
  
                strokeWeight(3);
}


                void 
                keyPressed() {
  
                if (trailOrLinked = !trailOrLinked)    
                noLoop();
  
                else                                   
                loop();
}


                void 
                mousePressed() {
  
                redraw();

  
                if (isFull) {
    tt = trails.remove();
    trails.
                add( 
                new PointXY(
                mouseX, 
                mouseY) );
  }

  
                else {
    trails.
                add( 
                new PointXY(
                mouseX, 
                mouseY) );
    tt = trails.element();
    
                if (++currTrailSize == maxTrailPoints)   isFull = 
                true;
  }
}


                void 
                draw() {
  
                background(0300);

  
                for (PointXY t: trails)    t.action();
}


                class PointXY {
  
                final 
                int x, y;

  PointXY(
                int px, 
                int py) {
    x = px;
    y = py;
  }

  
                void action() {
    
                line(tt.x, tt.y, x, y);
    tt = 
                this;
  }
}

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