Help with collision for 2D obstacles (Flocking)

Programming Questions

alistairh..

Help with collision for 2D obstacles (Flocking)

in Programming Questions • 5 months ago

Hi all,

I'm working with a group of architecture students, who are very new to programming (starting 1 day ago), and we've been tasked with developing a collision program to test crowd dynamics around small obstacles.

We've been lucky enough to find a sketch by Sabin Serban (whose sketch can be found here) http://www.openprocessing.org/sketch/82295), that can do most of what we would like to be able to do.

However, we're having problems with adding permanent geometry (to represent walls) that the balls can collide with - so that the velocity reverses and the ball bounces off of the rectangle/wall.

Here is the code we have so far. I'd appreciate some assistance in developing this.

Many thanks,

Alistair

Agent[] aArray;

PVector[] oArray;

float speedLimit = 1;

float perceptionDistance = 100;

float normalDistance = 10;

float privacyDistance = 10;

boolean pause;

PImage img;

void setup() {

img = loadImage("PICCADILLY GARDENS MAP.jpg");

size(750,532);

background(img);

aArray = new Agent[300];

oArray = new PVector[0];

for (int i=0; i<aArray.length; i++) {

aArray[i] = new Agent(round(random(width)), round(random(height)), i);

}

pause = false;

}

void draw() {

background(img);

noStroke();

fill(255,200);

rect(0,0,width,height);

fill(0);

for (int i=0; i<aArray.length; i++) {

aArray[i].drawMe();

aArray[i].getNeighbors(perceptionDistance, privacyDistance);

}

for (int i=0; i<oArray.length; i++) {

fill(255,0,0);

ellipse(oArray[i].x, oArray[i].y, 5, 5);

}

for (int i=0; i<aArray.length; i++) {

aArray[i].update();

}

void mousePressed() {

if (mouseButton == RIGHT) {

if (pause) {

loop();

pause = false;

}else{

noLoop();

pause = true;

}

}else if (mouseButton == LEFT) {

PVector newObst = new PVector(mouseX, mouseY);

oArray = (PVector[]) append(oArray, newObst);

}

void keyPressed(){

if (key == 'r'){

rect(mouseX,mouseY,60,7);

fill(0);

}

class Agent {

PVector pos, dir, target;

int nb[];

float vel;

int count;

Agent(int x, int y, int c) {

pos = new PVector(x, y);

dir = new PVector(random(4)-2,random(4)-2);

dir.normalize();

dir.mult(speedLimit);

vel = random(2, speedLimit);

count = c;

}

void getNeighbors(float dirRadius, float posRadius) {

nb = new int[0];

// println(count);

for(int i=0; i<aArray.length; i++) {

if (i != count) {

float delta = PVector.dist(pos, aArray[i].pos);

// println(i + " " + delta);

if (delta < dirRadius) {

nb = append(nb, i);

}

void getDirVel() {

float clearDist = perceptionDistance;

PVector newDir = new PVector(0,0);

PVector newPos = new PVector(0,0);

PVector newVar = new PVector(0,0);

PVector newAwa = new PVector(0,0);

for (int i=0; i<nb.length; i++) {

newDir.add(aArray[nb[i]].dir);

float delta = PVector.dist(aArray[nb[i]].pos, pos);

if ((delta > privacyDistance) && (clearDist > privacyDistance)) {

newVar.add(PVector.sub(aArray[nb[i]].pos, pos));

}else if ((clearDist > delta)&&(delta < privacyDistance)) {

newPos = PVector.sub(pos, aArray[nb[i]].pos);

clearDist = delta;

}

for (int i=0; i<oArray.length; i++) {

float delta = PVector.dist(oArray[i], pos);

if (delta < normalDistance) {

newAwa.add(PVector.sub(pos, oArray[i]));

}

newDir.normalize();

newPos.normalize();

newVar.normalize();

newAwa.normalize();

//first modify dir to conform to flock behaviour

newDir.mult(0.1);

dir.add(newDir);

dir.limit(speedLimit);

if (clearDist > normalDistance) {

// if too far from flock get closer

newVar.mult(0.01);

dir.add(newVar);

}else if (clearDist < privacyDistance){

// if too close to neighbour move away but keep speed constant

newPos.mult(0.01);

dir.add(newPos);

dir.limit(speedLimit);

}

// if any obstacle in privacy distance move to avoid obstacle

newAwa.mult(0.3);

dir.add(newAwa);

dir.limit(speedLimit);

}

void detectEdges() {

if (pos.x>width) {pos.x = 0;};

if (pos.x<0) {pos.x = width;};

if (pos.y>height) {pos.y = 0;};

if (pos.y<0) {pos.y = height;};

}

void update() {

getDirVel();

pos.add(dir);

detectEdges();

}

void drawMe() {

stroke(0);

fill(0);

ellipse(pos.x,pos.y,4,4);

/* stroke(255,0,0);

noFill();

ellipse(pos.x,pos.y,perceptionDistance,perceptionDistance);

stroke(0,0,255);

ellipse(pos.x,pos.y,privacyDistance,privacyDistance);

*/} //circles that show the perception radius and the privacy radius

}

Replies(1)

benj.n.su..

Re: Help with collision for 2D obstacles (Flocking)

5 months ago

EDIT: Formerly there was a bit in here about part of the problem being in lines 130-142. that was incorrect. Those work as expected. Apologies.

In your edge detection function, you are only changing position, not the direction. As you have it right now, it says "if you reach the edge at (someX, height) move my agent to a position of (someX, 0). So your agent magically jumps to the top of the screen when it hits the bottom but continues in the same direction.

//LINES 150-155

void detectEdges() {

if (pos.x>width) {pos.x = 0;};

if (pos.x<0) {pos.x = width;};

if (pos.y>height) {pos.y = 0;};

if (pos.y<0) {pos.y = height;};

}

What you want to do is change the direction but not it's position. You can change direction when you hit a wall simply by multiplying the pos.x, or pos.y of the agent by -1. Suppose you have a vector velocity that is changing the pos.x, pos.y of the vector by adding (2, 2). This would move your agent down and to the right of the sketch two pixels per draw. Now, multiply the pos.y by -1. The velocity vector will change to (2, -2) causing the agent to move up and to the right by 2 pixels. Multiply the pos.y by -1 again and your velocity will once again by (2, 2) moving 2 pixels down and to the right.

To get a better understanding of this principle check out the following (note, in the examples sometimes you'll see speed in place of velocity, since speed is change in velocity over time and the time in processing is the frameRate. Magnitude is also often used in place of direction.)

NON VECTOR BASED EXAMPLES:

Processing Handbook:

PDE>>FILE>>EXAMPLES>>BOOKS>UNITS 31-42>>31 Motion 1>>Ex_02 and Ex_03

PDE>>FILE>>EXAMPLES>>BOOKS>UNITS 43-41>>50 Simulate 2>>Ex_11 and 50_12

The Nature of Code by Daniel Shiffman

Example 1.1: http://natureofcode.com/book/chapter-1-vectors/

VECTOR BASED EXAMPLES

The Nature of Code by Daniel Shiffman

The rest of Chapter 1 - Vectors: http://natureofcode.com/book/chapter-1-vectors/

All of Chapter 6 - Autonomous Agents: http://natureofcode.com/book/chapter-6-autonomous-agents/'

***SPOILER ALERT*** Chapter 6 of NOC will show you how to do *exactly* what you want to do. Sometimes that's not as fun as building and breaking the models in your head on your own with your own solutions even if they aren't the most elegant ones. With regard to your specific question, stay away from example 6.3, or if you just want the answer, flock towards it (har har).

Some other notes:

Your starting velocity for your Agent is: vel = random(2, speedLimit); However, this means that your vel will always by 2 because the random function must have variables where the first is less than the right otherwise it defaults to the first.

Top Reply