Changing direction of the ball after collision - javascript

I have written this code to demonstrate a basic visual p5js project. In here there are 10 balls of varying sizes and colors that spawn at random positions, move around in the canvas and might collide with each other. I am not looking for elastic collision or "realistic" collision physics for that matter. I just want the balls to change to a different direction (can be random as long as it works) and work accordingly.
Here is my code :
class Ball {
//create new ball using given arguments
constructor(pos, vel, radius, color) {
this.pos = pos;
this.vel = vel;
this.radius = radius;
this.color = color;
}
//collision detection
collide(check) {
if (check == this) {
return;
}
let relative = p5.Vector.sub(check.pos, this.pos);
let dist = relative.mag() - (this.radius + check.radius);
if (dist < 0) { //HELP HERE! <--
this.vel.mult(-1);
check.vel.mult(-1);
}
}
//give life to the ball
move() {
this.pos.add(this.vel);
if (this.pos.x < this.radius) {
this.pos.x = this.radius;
this.vel.x = -this.vel.x;
}
if (this.pos.x > width - this.radius) {
this.pos.x = width - this.radius;
this.vel.x = -this.vel.x;
}
if (this.pos.y < this.radius) {
this.pos.y = this.radius;
this.vel.y = -this.vel.y;
}
if (this.pos.y > height - this.radius) {
this.pos.y = height - this.radius;
this.vel.y = -this.vel.y;
}
}
//show the ball on the canvas
render() {
fill(this.color);
noStroke();
ellipse(this.pos.x, this.pos.y, this.radius * 2);
}
}
let balls = []; //stores all the balls
function setup() {
createCanvas(window.windowWidth, window.windowHeight);
let n = 10;
//loop to create n balls
for (i = 0; i < n; i++) {
balls.push(
new Ball(
createVector(random(width), random(height)),
p5.Vector.random2D().mult(random(5)),
random(20, 50),
color(random(255), random(255), random(255))
)
);
}
}
function draw() {
background(0);
//loop to detect collision at all instances
for (let i = 0; i < balls.length; i++) {
for (let j = 0; j < i; j++) {
balls[i].collide(balls[j]);
}
}
//loop to render and move all balls
for (let i = 0; i < balls.length; i++) {
balls[i].move();
balls[i].render();
}
}
Here is a link to the project : https://editor.p5js.org/AdilBub/sketches/TNn2OREsN
All I need is the collision to change the direction of the ball to a random direction and not get stuck. Any help would be appreciated. I am teaching kids this program so I just want basic collision, doesnot have to be "realistic".
Any help is appreciated. Thank you.

The issues you are currently encountering with balls being stuck has to do with randomly generating balls that overlap such that after one iteration of movement they still overlap. When this happens both balls will simply oscillate in place repeatedly colliding with each other. You can prevent this simply by checking for collisions before adding new balls:
class Ball {
//create new ball using given arguments
constructor(pos, vel, radius, color) {
this.pos = pos;
this.vel = vel;
this.radius = radius;
this.color = color;
}
isColliding(check) {
if (check == this) {
return;
}
let relative = p5.Vector.sub(check.pos, this.pos);
let dist = relative.mag() - (this.radius + check.radius);
return dist < 0;
}
//collision detection
collide(check) {
if (this.isColliding(check)) {
this.vel.x *= -1;
this.vel.y *= -1;
check.vel.x *= -1;
check.vel.y *= -1;
}
}
//give life to the ball
move() {
this.pos.add(this.vel);
if (this.pos.x < this.radius) {
this.pos.x = this.radius;
this.vel.x = -this.vel.x;
}
if (this.pos.x > width - this.radius) {
this.pos.x = width - this.radius;
this.vel.x = -this.vel.x;
}
if (this.pos.y < this.radius) {
this.pos.y = this.radius;
this.vel.y = -this.vel.y;
}
if (this.pos.y > height - this.radius) {
this.pos.y = height - this.radius;
this.vel.y = -this.vel.y;
}
}
//show the ball on the canvas
render() {
fill(this.color);
noStroke();
ellipse(this.pos.x, this.pos.y, this.radius * 2);
}
}
let balls = []; //stores all the balls
function setup() {
createCanvas(500, 500);
let n = 10;
//loop to create n balls
for (i = 0; i < n; i++) {
let newBall =
new Ball(
createVector(random(width), random(height)),
p5.Vector.random2D().mult(random(5)),
random(20, 40),
color(random(255), random(255), random(255))
);
let isOk = true;
// check for collisions with existing balls
for (let j = 0; j < balls.length; j++) {
if (newBall.isColliding(balls[j])) {
isOk = false;
break;
}
}
if (isOk) {
balls.push(newBall);
} else {
// try again
i--;
}
}
}
function draw() {
background(0);
//loop to detect collision at all instances
for (let i = 0; i < balls.length; i++) {
for (let j = 0; j < i; j++) {
balls[i].collide(balls[j]);
}
}
//loop to render and move all balls
for (let i = 0; i < balls.length; i++) {
balls[i].move();
balls[i].render();
}
}
<script src="https://cdnjs.cloudflare.com/ajax/libs/p5.js/1.4.0/p5.js"></script>
That said, fully elastic collisions (which means collisions are instantaneous and involve no loss of energy due to deformation and resulting heat emission) are actually quite simple to simulate. Here's a tutorial I made on OpenProcessing demonstrating the necessary concepts using p5.js: Elastic Ball Collision Tutorial.
Here's the final version of the code from that tutorial:
const radius = 30;
const speed = 100;
let time;
let balls = []
let boundary = [];
let obstacles = [];
let paused = false;
function setup() {
createCanvas(400, 400);
angleMode(DEGREES);
ellipseMode(RADIUS);
boundary.push(createVector(60, 4));
boundary.push(createVector(width - 4, 60));
boundary.push(createVector(width - 60, height - 4));
boundary.push(createVector(4, height - 60));
obstacles.push(createVector(width / 2, height / 2));
balls.push({
pos: createVector(width * 0.25, height * 0.25),
vel: createVector(speed, 0).rotate(random(0, 360))
});
balls.push({
pos: createVector(width * 0.75, height * 0.75),
vel: createVector(speed, 0).rotate(random(0, 360))
});
balls.push({
pos: createVector(width * 0.25, height * 0.75),
vel: createVector(speed, 0).rotate(random(0, 360))
});
time = millis();
}
function keyPressed() {
if (key === "p") {
paused = !paused;
time = millis();
}
}
function draw() {
if (paused) {
return;
}
deltaT = millis() - time;
time = millis();
background('dimgray');
push();
fill('lightgray');
stroke('black');
strokeWeight(2);
beginShape();
for (let v of boundary) {
vertex(v.x, v.y);
}
endShape(CLOSE);
pop();
push();
fill('dimgray');
for (let obstacle of obstacles) {
circle(obstacle.x, obstacle.y, radius);
}
pop();
for (let i = 0; i < balls.length; i++) {
let ball = balls[i];
// update position
ball.pos = createVector(
min(max(0, ball.pos.x + ball.vel.x * (deltaT / 1000)), width),
min(max(0, ball.pos.y + ball.vel.y * (deltaT / 1000)), height)
);
// check for collisions
for (let i = 0; i < boundary.length; i++) {
checkCollision(ball, boundary[i], boundary[(i + 1) % boundary.length]);
}
for (let obstacle of obstacles) {
// Find the tangent plane that is perpendicular to a line from the obstacle to
// the moving circle
// A vector pointing in the direction of the moving object
let dirVector = p5.Vector.sub(ball.pos, obstacle).normalize().mult(radius);
// The point on the perimiter of the obstacle that is in the direction of the
// moving object
let p1 = p5.Vector.add(obstacle, dirVector);
checkCollision(ball, p1, p5.Vector.add(p1, p5.Vector.rotate(dirVector, -90)));
}
// Check for collisions with other balls
for (let j = 0; j < i; j++) {
let other = balls[j];
let distance = dist(ball.pos.x, ball.pos.y, other.pos.x, other.pos.y);
if (distance / 2 < radius) {
push();
let midPoint = p5.Vector.add(ball.pos, other.pos).div(2);
let boundaryVector = p5.Vector.sub(other.pos, ball.pos).rotate(-90);
let v1Parallel = project(ball.vel, boundaryVector);
let v2Parallel = project(other.vel, boundaryVector);
let v1Perpendicular = p5.Vector.sub(ball.vel, v1Parallel);
let v2Perpendicular = p5.Vector.sub(other.vel, v2Parallel);
ball.vel = p5.Vector.add(v1Parallel, v2Perpendicular);
other.vel = p5.Vector.add(v2Parallel, v1Perpendicular);
let bounce = min(radius, 2 * radius - distance);
ball.pos.add(p5.Vector.rotate(boundaryVector, -90).normalize().mult(bounce));
other.pos.add(p5.Vector.rotate(boundaryVector, 90).normalize().mult(bounce));
pop();
}
}
}
// Only draw balls after all position updates are complete
for (let ball of balls) {
circle(ball.pos.x, ball.pos.y, radius);
}
}
function drawLine(origin, offset) {
line(origin.x, origin.y, origin.x + offset.x, origin.y + offset.y);
}
// Handles collision with a plane given two points on the plane.
// It is assumed that given a vector from p1 to p2, roating that vector
// clockwise 90 degrees will give a vector pointing to the in-bounds side of the
// plane (i.e. a "normal").
function checkCollision(ball, p1, p2) {
let boundaryVector = p5.Vector.sub(p2, p1);
let objVector = p5.Vector.sub(ball.pos, p1);
let angle = boundaryVector.angleBetween(objVector);
let distance = objVector.mag() * sin(angle);
if (distance <= radius) {
// Collision
let vParallel = project(ball.vel, boundaryVector);
let vPerpendicular = p5.Vector.sub(ball.vel, vParallel);
ball.vel = p5.Vector.add(vParallel, p5.Vector.mult(vPerpendicular, -1));
let bounce = min(radius, (radius - distance) * 2);
// If the ball has crossed over beyond the plane we want to offset it to be on
// the in-bounds side of the plane.
let bounceOffset = p5.Vector.rotate(boundaryVector, 90).normalize().mult(bounce);
ball.pos.add(bounceOffset);
}
}
// p5.Vector helpers
function project(vect1, vect2) {
vect2 = p5.Vector.normalize(vect2);
return p5.Vector.mult(vect2, p5.Vector.dot(vect1, vect2));
}
function reject(vect1, vect2) {
return p5.Vector.sub(vect1, project(vect1, vect2));
}
<script src="https://cdnjs.cloudflare.com/ajax/libs/p5.js/1.4.0/p5.js"></script>

Related

My code is not drawing bars to the screen from an array

I am trying to make one of those sorting algorithms and want to have the bars get randomly generated with height and x position. However, when I run the code, it doesn't draw any bars. I'm also not getting any errors sent so I have no idea what's going wrong.
class Bar {
constructor(x, height) {
this.height = height;
this.size = 10;
this.x = x;
}
draw() {
fill("blue");
rect(this.x * this.size, height - (this.height * this.size), this.size, this.height * this.size);
}
}
let bars = [];
function setup() {
createCanvas(400, 400);
generateBars();
}
function generateBars() {
for (let i = 0; i < 39; i++) {
randomX = random(0, 39);
randomHeight = random(0, 40)
for (let j = 0; j < bars.length; j++) {
if (bars[j].x == randomX) {
randomX = random(0, 39);
} else {
for (let h = 0; h < bars.length; h++) {
if (bars[j].height == randomHeight) {
randomHeight = random(0, 40);
} else {
bars[i] = new Bar(randomX, randomHeight);
}
}
}
}
}
}
function draw() {
background(220);
for (let k = 0; k < bars.length; k++) {
bars[k].draw();
}
}
<script src="https://cdnjs.cloudflare.com/ajax/libs/p5.js/1.5.0/p5.min.js"></script>
The logic in generateBars seems convoluted and the intention is unclear.
As far as I see Bar's x property acts more of a value property storing the number to be sorted later because it is multiplied by size in draw(). (e.g. x is not the final x position the bar should be rendered at, as it's name implies).
I would simply intanstiate Bar like so:
class Bar{
constructor(x, height){
this.height = height;
this.size = 10;
this.x = x;
}
draw(){
fill("blue");
rect(this.x * this.size, height - (this.height * this.size), this.size, this.height * this.size);
}
}
let bars = [];
function setup() {
createCanvas(400, 400);
generateBars();
}
function generateBars(){
for(let i = 0; i < 40; i++){
randomHeight = random(0, 40)
bars[i] = new Bar(i, randomHeight);
}
}
function draw() {
background(220);
for(let k = 0; k < bars.length; k++){
bars[k].draw();
}
}
function mouseClicked(){
setup();
}
<script src="https://cdnjs.cloudflare.com/ajax/libs/p5.js/1.5.0/p5.min.js"></script>
(I've added a hacky mouseClicked() handler so it's easy to regenerate the bars for testing/debugging purposes. You may not need it in your final code)
Update Based on your comment, it's the bar height that is tightly coupled to the value to be sorted later.
One idea is to simply pre-generate the list of numbers to sort and shuffle() them first:
class Bar{
constructor(x, height){
this.height = height;
this.size = 10;
this.x = x;
}
draw(){
fill("blue");
rect(this.x * this.size, height - (this.height * this.size), this.size, this.height * this.size);
}
}
let bars = [];
function setup() {
createCanvas(400, 400);
generateBars();
}
function generateBars(){
// array to be sorted
let barValues = [];
for(let i = 0; i < 40; i++){
// values are sorted first
barValues[i] = i;
}
// then we shuffle them: second argument = shuffle in place (replacing the old array)
shuffle(barValues, true);
// assign shuffled values to Bar instances
for(let i = 0; i < 40; i++){
bars[i] = new Bar(i, barValues[i]);
}
}
function draw() {
background(220);
for(let k = 0; k < bars.length; k++){
bars[k].draw();
}
}
function mouseClicked(){
setup();
}
<script src="https://cdnjs.cloudflare.com/ajax/libs/p5.js/1.5.0/p5.min.js"></script>

Why are my objects overlapping in my p5.js project?

I'm working on a project where I simulate physics with balls.
Here is the link to the p5 editor of the project.
My problem is the following, when I add a lot of ball (like 200), balls are stacking but some of them will eventually collapse and I don't know why.
Can somebody explain why it does this and how to solve the problem ?
Thanks.
Here is the code of the sketch.
document.oncontextmenu = function () {
return false;
}
let isFlushing = false;
let isBallDiameterRandom = false;
let displayInfos = true;
let displayWeight = false;
let clickOnce = false;
let FRAME_RATE = 60;
let SPEED_FLUSH = 3;
let Y_GROUND;
let lastFR;
let balls = [];
function setup() {
frameRate(FRAME_RATE);
createCanvas(window.innerWidth, window.innerHeight);
Y_GROUND = height / 20 * 19;
lastFR = FRAME_RATE;
}
function draw() {
background(255);
if (isFlushing) {
for (let i = 0; i < SPEED_FLUSH; i++) {
balls.pop();
}
if (balls.length === 0) {
isFlushing = false;
}
}
balls.forEach(ball => {
ball.collide();
ball.move();
ball.display(displayWeight);
ball.checkCollisions();
});
if (mouseIsPressed) {
let ballDiameter;
if (isBallDiameterRandom) {
ballDiameter = random(15, 101);
} else {
ballDiameter = 25;
}
if (canAddBall(mouseX, mouseY, ballDiameter)) {
isFlushing = false;
let newBall = new Ball(mouseX, mouseY, ballDiameter, balls);
if (mouseButton === LEFT && !clickOnce) {
balls.push(newBall);
clickOnce = true;
}
if (mouseButton === RIGHT) {
balls.push(newBall);
}
}
}
drawGround();
if (displayInfos) {
displayShortcuts();
displayFrameRate();
displayBallCount();
}
}
function mouseReleased() {
if (mouseButton === LEFT) {
clickOnce = false;
}
}
function keyPressed() {
if (keyCode === 32) {//SPACE
displayInfos = !displayInfos;
}
if (keyCode === 70) {//F
isFlushing = true;
}
if (keyCode === 71) {//G
isBallDiameterRandom = !isBallDiameterRandom;
}
if (keyCode === 72) {//H
displayWeight = !displayWeight;
}
}
function canAddBall(x, y, d) {
let isInScreen =
y + d / 2 < Y_GROUND &&
y - d / 2 > 0 &&
x + d / 2 < width &&
x - d / 2 > 0;
let isInAnotherBall = false;
for (let i = 0; i < balls.length; i++) {
let d = dist(x, y, balls[i].position.x, balls[i].position.y);
if (d < balls[i].w) {
isInAnotherBall = true;
break;
}
}
return isInScreen && !isInAnotherBall;
}
function drawGround() {
strokeWeight(0);
fill('rgba(200,200,200, 0.25)');
rect(0, height / 10 * 9, width, height / 10);
}
function displayFrameRate() {
if (frameCount % 30 === 0) {
lastFR = round(frameRate());
}
textSize(50);
fill(255, 0, 0);
let lastFRWidth = textWidth(lastFR);
text(lastFR, width - lastFRWidth - 25, 50);
textSize(10);
text('fps', width - 20, 50);
}
function displayBallCount() {
textSize(50);
fill(255, 0, 0);
text(balls.length, 10, 50);
let twBalls = textWidth(balls.length);
textSize(10);
text('balls', 15 + twBalls, 50);
}
function displayShortcuts() {
let hStart = 30;
let steps = 15;
let maxTW = 0;
let controlTexts = [
'LEFT CLICK : add 1 ball',
'RIGHT CLICK : add 1 ball continuously',
'SPACE : display infos',
'F : flush balls',
'G : set random ball diameter (' + isBallDiameterRandom + ')',
'H : display weight of balls (' + displayWeight + ')'
];
textSize(11);
fill(0);
for (let i = 0; i < controlTexts.length; i++) {
let currentTW = textWidth(controlTexts[i]);
if (currentTW > maxTW) {
maxTW = currentTW;
}
}
for (let i = 0; i < controlTexts.length; i++) {
text(controlTexts[i], width / 2 - maxTW / 2 + 5, hStart);
hStart += steps;
}
fill(200, 200, 200, 100);
rect(width / 2 - maxTW / 2,
hStart - (controlTexts.length + 1) * steps,
maxTW + steps,
(controlTexts.length + 1) * steps - steps / 2
);
}
Here is the code of the Ball class.
class Ball {
constructor(x, y, w, e) {
this.id = e.length;
this.w = w;
this.e = e;
this.progressiveWidth = 0;
this.rgb = [
floor(random(0, 256)),
floor(random(0, 256)),
floor(random(0, 256))
];
this.mass = w;
this.position = createVector(x + random(-1, 1), y);
this.velocity = createVector(0, 0);
this.acceleration = createVector(0, 0);
this.gravity = 0.2;
this.friction = 0.5;
}
collide() {
for (let i = this.id + 1; i < this.e.length; i++) {
let dx = this.e[i].position.x - this.position.x;
let dy = this.e[i].position.y - this.position.y;
let distance = sqrt(dx * dx + dy * dy);
let minDist = this.e[i].w / 2 + this.w / 2;
if (distance < minDist) {
let angle = atan2(dy, dx);
let targetX = this.position.x + cos(angle) * minDist;
let targetY = this.position.y + sin(angle) * minDist;
this.acceleration.set(
targetX - this.e[i].position.x,
targetY - this.e[i].position.y
);
this.velocity.sub(this.acceleration);
this.e[i].velocity.add(this.acceleration);
//TODO : Effets bizarre quand on empile les boules (chevauchement)
this.velocity.mult(this.friction);
}
}
}
move() {
this.velocity.add(createVector(0, this.gravity));
this.position.add(this.velocity);
}
display(displayMass) {
if (this.progressiveWidth < this.w) {
this.progressiveWidth += this.w / 10;
}
stroke(0);
strokeWeight(2);
fill(this.rgb[0], this.rgb[1], this.rgb[2], 100);
ellipse(this.position.x, this.position.y, this.progressiveWidth);
if (displayMass) {
strokeWeight(1);
textSize(10);
let tempTW = textWidth(int(this.w));
text(int(this.w), this.position.x - tempTW / 2, this.position.y + 4);
}
}
checkCollisions() {
if (this.position.x > width - this.w / 2) {
this.velocity.x *= -this.friction;
this.position.x = width - this.w / 2;
} else if (this.position.x < this.w / 2) {
this.velocity.x *= -this.friction;
this.position.x = this.w / 2;
}
if (this.position.y > Y_GROUND - this.w / 2) {
this.velocity.x -= this.velocity.x / 100;
this.velocity.y *= -this.friction;
this.position.y = Y_GROUND - this.w / 2;
} else if (this.position.y < this.w / 2) {
this.velocity.y *= -this.friction;
this.position.y = this.w / 2;
}
}
}
I see this overlapping happen when the sum of ball masses gets bigger than the elasticity of the balls. At least it seems so. I made a copy with a smaller pool so it doesn't take so much time to reproduce the problem.
In the following example, with 6 balls (a mass of 150 units) pressing on the base row, we see that the 13 balls in the base row overlap. The base row has a width of ca. 300 pixels, which is only enough space for 12 balls of diameter 25. I think this is showing the limitation of the model: the balls are displayed circular but indeed have an amount of elasticity that they should display deformed instead. It's hard to say how this can be fixed without implementing drawing complicated shapes. Maybe less friction?
BTW: great physics engine you built there :-)
Meanwhile I was able to make another screenshot with even fewer balls. The weight of three of them (eq. 75 units) is sufficient to create overlapping in the base row.
I doubled the size of the balls and changed the pool dimensions as to detedt that there is a more serious error in the engine. I see that the balls are pressed so heavily under pressure that they have not enough space for their "volume" (area). Either they have to implode or it's elastic counter force must have greater impact of the whole scene. If you pay close attention to the pendulum movements made by the balls at the bottom, which have the least space, you will see that they are very violent, but apparently have no chance of reaching the outside.
Could it be that your evaluation order
balls.forEach(ball => {
ball.collide();
ball.move();
ball.display(displayWeight);
ball.checkCollisions();
});
is not able to propagate the collisions in a realistic way?

My gravity simulation gets stuck

I am making a gravity simulator to get the feel for physics based coding and I have made an idea here. But I have a problem, after some point after bouncing, the particle (square) gets stuck bouncing to the same point. Does anyone know why?
Heres a link to the jsfiddle: https://jsfiddle.net/jjndeokk/6/
var c = document.getElementById("canvas");
var ctx = c.getContext("2d");
var gravity, objectDensity, force;
gravity = 10.8;
function Object(mass, x, y, w, h, acc, hacc) {
this.m = mass;
this.x = x;
this.y = y;
this.w = w;
this.h = h;
this.a = acc;
this.ha = hacc;
};
var particle = [];
var rows = [1];
for (let i = 0, len = rows.length; i < len; i++) {
particle.push(new Object(10, i * 30, 10, 20, 20, 0, 0));
};
function draw() {
ctx.clearRect(0, 0, c.width, c.height)
for (let i = 0, len = particle.length; i < len; i++) {
ctx.fillRect(particle[i].x, particle[i].y, particle[i].w, particle[i].h)
particle[i].a += gravity;
particle[i].ha = 3;
particle[i].x += particle[i].ha;
if (particle[i].y + particle[i].h + particle[i].a > c.height) {
particle[i].y = c.height - particle[i].h;
} else {
particle[i].y += particle[i].a;
}
}
}
function update() {
for (let i = 0, len = particle.length; i < len; i++) {
if (particle[i].a >= 0) {
if (particle[i].y + particle[i].h >= c.height) {
particle[i].a *= -1;
}
}
}
draw();
}
setInterval(update, 60);
The main reason your bounce gets stuck is that you are applying gravity to the dot even when it is on the ground. After that, you reverse its velocity and it flies back up into the air.
You need to check whether it's on the ground and not apply gravity if it is:
if (isAboveFloor(particle)) {
particle.a += gravity;
}
Once that's fixed, what you'll actually find is that the bounce goes back and forth between its initial height and the ground, and this is to be expected - it's conservation of momentum.
In order to make the bounce more realistic, you need to introduce a "coefficient of restitution" that is less than 1:
if (particle.y + particle.h >= c.height) {
particle.a *= -cRest; // cRest is between 0 and 1
}
Once that's done, you get a pretty nice simulation: https://jsfiddle.net/jjndeokk/17/
I've also made the following modifications:
Used .forEach so that the code isn't completely littered with [i]s
Made the gravity and velocity calculations take time into account
Renamed particle.a and particle.ha to particle.vy and particle.vx because those properties were measuring velocity, not acceleration.
Moved all of the calculations into the update() function so you don't have most of them in the draw() function.
var c = document.getElementById("canvas");
var ctx = c.getContext("2d");
var gravity, objectDensity, force;
gravity = 240; // pixels / second / second
var cRest = 0.6;
var interval = 60;
var secondsPerInterval = interval / 1000;
function Object(mass, x, y, w, h, vxi, vyi) {
this.m = mass;
this.x = x;
this.y = y;
this.w = w;
this.h = h;
this.vx = vxi;
this.vy = vyi;
};
var particles = [];
var rows = [1];
for (let i = 0, len = rows.length; i < len; i++) {
particles.push(new Object(10, i * 30, 10, 20, 20, 40, 0));
};
function draw() {
ctx.clearRect(0, 0, c.width, c.height);
particles.forEach(function(particle) {
ctx.fillRect(particle.x, particle.y, particle.w, particle.h);
})
}
function isAboveFloor(particle) {
return Math.abs(particle.y + particle.h - c.height) > 1;
}
function update() {
particles.forEach(function(particle) {
if (particle.vy < 0 || isAboveFloor(particle)) {
particle.x += particle.vx * secondsPerInterval;
particle.y = Math.min(particle.y + particle.vy * secondsPerInterval, c.height - particle.h);
// if still above floor, accelerate
if(isAboveFloor(particle)){
particle.vy += gravity * secondsPerInterval;
}
}
if (particle.vy >= 0 && particle.y + particle.h >= c.height) {
particle.vy *= -cRest;
}
console.log(particle);
});
draw();
}
setInterval(update, interval);
<canvas id="canvas" height="600" width="800"></canvas>

HTML5 Canvas draw line distance between points

I'm trying to learn HTML5 and found a very simple particle system wich i modded a bit.
I would like to create a line, between particles, if the distance between the particles is within the range 0-20.
What I currently have draws a line between every particle, no matter the distance.
This is where I try to check the distance, but I can't figure out how to do this. Would appreciate any help and explanations. Thanks in advance.
// This particle
var p = particles[t];
// Check position distance to other particles
for (var q = 0; q < particles.length; q++) {
if (particles[q].x - p.x < line_distance || p.x - particles[q].x < line_distance) {
ctx.beginPath();
ctx.lineWidth = .1;
ctx.strokeStyle = '#fff';
ctx.moveTo(p.x, p.y);
ctx.lineTo(particles[q].x, particles[q].y);
ctx.stroke();
}
}
// Request animation frame
var requestAnimationFrame = window.requestAnimationFrame ||
window.mozRequestAnimationFrame ||
window.webkitRequestAnimationFrame ||
window.msRequestAnimationFrame;
// Canvas
var canvas = document.getElementById('canvas');
var ctx = canvas.getContext('2d');
// Set fullscreen
canvas.width = document.documentElement.clientWidth;
canvas.height = document.documentElement.clientHeight;
// Options
var num =30; // Number of particles to draw
var size = 3; // Particle size
var color = '#fff'; // Particle color
var min_speed = 1; // Particle min speed
var max_speed = 3; // Particle max speed
var line_distance = 20; // This is the max distance between two particles
// if we want to draw a line between them
// Particles array
var particles = [];
for (var i = 0; i < num; i++) {
particles.push(
new create_particle()
);
}
// Lets animate the particle
function draw() {
// Background
ctx.fillStyle = "#000";
ctx.fillRect(0, 0, canvas.width, canvas.height);
// Lets draw particles from the array now
for (var t = 0; t < particles.length; t++) {
// This particle
var p = particles[t];
for (var q = 0; q < particles.length; q++) {
// Check position distance
if (particles[q].x - p.x < line_distance || p.x - particles[q].x < line_distance) {
ctx.beginPath();
ctx.lineWidth = .1;
ctx.strokeStyle = '#fff';
ctx.moveTo(p.x, p.y);
ctx.lineTo(particles[q].x, particles[q].y);
ctx.stroke();
}
}
// Color
ctx.fillStyle = color;
// Circle path
ctx.beginPath();
ctx.arc(p.x, p.y, p.radius, Math.PI * 2, false);
ctx.fill();
// Lets use the velocity now
p.x += p.vx;
p.y += p.vy;
// If there is only 1 particle
// show X, Y, and velocity
if (num === 1) {
ctx.fillText('Y:'+ p.y, 20, 20);
ctx.fillText('X:'+ p.x, 20, 40);
ctx.fillText('YV:'+ p.vy, 20, 60);
ctx.fillText('XV:'+ p.vx, 20, 80);
}
// To prevent the balls from moving out of the canvas
if (p.x < size) p.vx*= (p.vx / -p.vx);
if (p.y < size) p.vy*= (p.vy / -p.vy);
if (p.x > canvas.width - size) p.vx*= (-p.vx / p.vx);
if (p.y > canvas.height - size) p.vy*= (-p.vy / p.vy);
}
// Loop
requestAnimationFrame(draw);
}
// Function for particle creation
function create_particle() {
// Random position
this.x = Math.random() * canvas.width;
this.y = Math.random() * canvas.height;
// Velocity
this.vx = random_int_between(min_speed, max_speed);
this.vy = random_int_between(min_speed, max_speed);
// Color & Size
this.color = color;
this.radius = size;
}
// Random number between (used for speed)
function random_int_between(min, max) {
return Math.floor(Math.random() * max) + min;
}
draw();
<canvas id="canvas"></canvas>
N body Particle systems
As this is an N body case and no one said anything about CPU load.
CPU Load
Particle systems can quickly bog down a CPU in an overload of processing. This is particularly true when you are testing each particle against the other. As particle systems are almost always for realtime graphics ineffective coding can destroy the whole animation.
Do nothing not needed
First as you are only looking for a threshold distance you can optimise the calculations by not continuing to calculate as soon as you know that there is a fail in the test.
So set up the threshold distance
var dist = 20;
var distSq = dist * dist; // No need to square this inside loops
Then in the loop as you calculate test and continue. Assuming p1 and p2 are particles
x = p2.x-p1.x; // do x first
if((x *= x) < distSq){ // does it pass?? if not you have saved calculating y
y = p2.y-p1.y; // now do y as you know x is within distance
if(x + (y * y) < distSq){ // now you know you are within 20
// draw the line
Assuming only 1/6 will pass and 1/3 come close you save over half the CPU load. You will also notice that I don't use the CPU heavy sqrt of the distance. There is no need as there is a one to one match between a number and the square of a number. If the square root of a number is less than the distance so will the square of the number be less than the square of the distance.
N body Squared
Never do a N body sim with two for loops like this.
for(i = 0; i < particles.length; i ++){
for(j = 0; j < particles.length; j ++){
// you will test all i for j and all j for i but half of them are identical
// and the square root of the number are self to self
This hurts me just to look at as the solution is so so simple.
Assuming you have 100 particles at 60 frames a second you are doing 60 * 100 * 100 comparisons a second (600,000) for 100 particles. Thats is a total waste of CPU time.
Never do something twice, or that you know the answer to.
To improve the for loops and avoid testing distances you already know and testing how far each particle is from itself
var len = particles.length; // move the length out as it can be expensive
// and pointless as the value does not change;
for(i = 0; i < len; i ++){
for(j = i + 1; j < len; j ++){
// Now you only test each particle against each other once rather than twice
Thus with just a few simple characters (for(j = 0 becomes for(j = i + 1) you more than half the CPU load, from 600,000 comparisons down to less than 300,000
The human eye is easy to fool
Fooling the eye is the best way to get extra performance from your animations.
This is a visual effect and the human eye does not see pixels nor does it it see individual frames at 1/60th a second, but it does see a drop in frame rate. Creating a complex particle system can an excellent FX but if it drops the frame rate the benefit is lost. Take advantage of the fact that pixels are to small and 1/20th of a second is way beyond the human ability to find error is the best way to optimise FXs and add more bang per CPU tick.
The demo below has two particle sims. 100 points each. Any points that come within 49 pixels have a line drawn between them. One does all the stuff I demonstrated above the other sacrifices a little memory and a lot off acuracy and only calculates the distances between 1/3rd of the points every frame. As the max speed can be close to half the line length a frame, skipping 2 frames can make a line twice as long or two points be too close without a line. There is a massive CPU saving in doing this, but you can not pick which is which.
Click on which sim you think is skipping points to find out which is which.
var canvas = document.createElement("canvas");
canvas.width= 540;
canvas.height = 270;
var ctx = canvas.getContext("2d");
document.body.appendChild(canvas);
mouseX = 0;
mouseB = false;
function clickedFun(event){
mouseX = event.clientX
mouseB = true;
}
canvas.addEventListener("click",clickedFun);
var w = 250;
var h = 250;
var wh = w/2;
var hh = h/2;
var speedMax = 5;
var partSize = 2;
var count = 100
var grav = 1;
var pA1 = []; // particle arrays
var pA2 = [];
var PI2 = Math.PI * 2;
// populate particle arrays
for(var i = 0; i < count; i += 1){
// dumb list
pA1.push({
x : Math.random() * w,
y : Math.random() * h,
dx : (Math.random() -0.5)*speedMax,
dy : (Math.random() -0.5)*speedMax,
})
// smart list
pA2.push({
x : Math.random() * w,
y : Math.random() * h,
dx : (Math.random() -0.5)*speedMax,
dy : (Math.random() -0.5)*speedMax,
links : [], // add some memory
})
for(var j = 0; j < count; j += 1){
pA2[i].links[i] = false; // set memory to no links
}
}
// move and draw the dots. Just a simple gravity sim
function drawAll(parts){
var x,y,d;
var i = 0;
var len = parts.length;
var p;
ctx.beginPath();
for(;i < len; i++){
p = parts[i];
x = wh-p.x;
y = hh-p.y;
d = x*x + y*y;
x *= grav / d;
y *= grav / d;
p.dx += x;
p.dy += y;
p.x += p.dx;
p.y += p.dy;
if(p.x <= 0){
p.dx -= p.dx/2;
p.x = 1;
}else
if(p.x >= w){
p.dx -= p.dx/2;
p.x = w-1;
}
if(p.y <= 0){
p.dy -= p.dy/2;
p.y = 1;
}else
if(p.y >= h){
p.dy -= p.dy/2;
p.y = w-1;
}
ctx.moveTo(p.x+partSize,p.y)
ctx.arc(p.x,p.y,partSize,0,PI2)
}
ctx.fill();
}
//Old style line test. If two particles are less than dist apart
// draw a line between them
function linesBetween(parts,dist){
var distSq = dist*dist;
var x,y,d,j;
var i = 0;
var len = parts.length;
var p,p1;
ctx.beginPath();
for(; i < len; i ++){
p = parts[i];
for(j = i + 1; j < len; j ++){
p1 = parts[j];
x = p1.x-p.x;
if((x *= x) < distSq){
y = p1.y-p.y;
if(x + (y*y) < distSq){
ctx.moveTo(p.x,p.y);
ctx.lineTo(p1.x,p1.y)
}
}
}
}
ctx.stroke();
}
var counter = 0;// counter for multyplexing
// Fast version. As the eye can not posible see the differance of
// of 4 pixels over 1/30th of a second only caculate evey third
// particls
function linesBetweenFast(parts,dist){
var distSq = dist*dist;
var x,y,d,j,l;
var i = 0;
counter += 1;
var cc = counter % 3;
var wr,re;
var len = parts.length;
var p,p1;
var lineSet
ctx.beginPath();
for(; i < len; i ++){
p = parts[i];
l = p.links;
for(j = i + 1; j < len; j += 1){
p1 = parts[j];
if((j + cc)%3 === 0){ // only every third particle
lineSet = false; // test for diferance default to fail
x = p1.x-p.x;
if((x *= x) < distSq){
y = p1.y-p.y;
if(x + (y*y) < distSq){
lineSet = true; // yes this needs a line
}
}
l[j] = lineSet; // flag it as needing a line
}
if(l[j]){ // draw the line if needed
ctx.moveTo(p.x,p.y);
ctx.lineTo(p1.x,p1.y);
}
}
}
ctx.stroke();
}
var drawLines; // to hold the function that draws lines
// set where the screens are drawn
var left = 10;
var right = 10 * 2 + w;
// Now to not cheat swap half the time
if(Math.random() < 0.5){
right = 10;
left = 10 * 2 + w;
}
// draws a screem
var doScreen = function(parts){
ctx.fillStyle = "red"
drawAll(parts);
ctx.strokeStyle = "black";
ctx.lineWidth = 1;
drawLines(parts,49);
}
var guess = ""
var guessPos;
var gueesCol;
ctx.font = "40px Arial Black";
ctx.textAlign = "center";
ctx.textBasline = "middle"
var timer = 0;
function update(){
ctx.setTransform(1,0,0,1,0,0);
ctx.clearRect(0,0,canvas.width,canvas.height);
ctx.setTransform(1,0,0,1,left,10);
ctx.strokeStyle = "red";
ctx.lineWidth = 4;
ctx.strokeRect(0,0,w,h);
drawLines = linesBetween;
doScreen(pA1)
ctx.setTransform(1,0,0,1,right,10);
ctx.strokeStyle = "red";
ctx.lineWidth = 4;
ctx.strokeRect(0,0,w,h);
drawLines = linesBetweenFast
doScreen(pA2)
if(mouseB){
if((mouseX > 270 && right >250) ||
(mouseX < 250 && right < 250)){
guess = "CORRECT!"
guessPos = right;
guessCol = "Green";
}else{
guess = "WRONG"
guessPos = left
guessCol = "Red";
}
timer = 120;
mouseB = false;
}else
if(timer > 0){
timer -= 1;
if(timer > 30){
ctx.setTransform(1,0,0,1,guessPos,10);
ctx.font = "40px Arial Black";
ctx.fillStyle = guessCol;
ctx.fillText(guess,w/2,h/2);
}else{
if(Math.random() < 0.5){
right = 10;
left = 10 * 2 + w;
}else{
left = 10;
right = 10 * 2 + w;
}
}
}else{
ctx.setTransform(1,0,0,1,0,0);
ctx.font = "16px Arial Black";
var tw = ctx.measureText("Click which sim skips 2/3rd of").width +30;
ctx.beginPath();
ctx.fillStyle = "#DDD";
ctx.strokeStyle = "Red";
ctx.rect(270-tw/2,-5,tw,40);
ctx.stroke();
ctx.fill();
ctx.fillStyle = "blue";
ctx.fillText("Click which sim skips 2/3rd of",270,15) ;
ctx.fillText("particle tests every frame",270,30) ;
}
requestAnimationFrame(update);
}
update();
This is just your test which is wrong.
a-b < c || b-a < c is always true (except if a-b == c)
replace by abs(a-b) < c if you want to test "x" distance, or by using the above formula if you want an euclidian distance
// Request animation frame
var requestAnimationFrame = window.requestAnimationFrame ||
window.mozRequestAnimationFrame ||
window.webkitRequestAnimationFrame ||
window.msRequestAnimationFrame;
// Canvas
var canvas = document.getElementById('canvas');
var ctx = canvas.getContext('2d');
// Set fullscreen
canvas.width = document.documentElement.clientWidth;
canvas.height = document.documentElement.clientHeight;
// Options
var num =30; // Number of particles to draw
var size = 3; // Particle size
var color = '#fff'; // Particle color
var min_speed = 1; // Particle min speed
var max_speed = 3; // Particle max speed
var line_distance = 20; // This is the max distance between two particles
// if we want to draw a line between them
// Particles array
var particles = [];
for (var i = 0; i < num; i++) {
particles.push(
new create_particle()
);
}
// Lets animate the particle
function draw() {
// Background
ctx.fillStyle = "#000";
ctx.fillRect(0, 0, canvas.width, canvas.height);
// Lets draw particles from the array now
for (var t = 0; t < particles.length; t++) {
// This particle
var p = particles[t];
for (var q = 0; q < particles.length; q++) {
// Check position distance
if (Math.abs(particles[q].x - p.x) < line_distance) {
ctx.beginPath();
ctx.lineWidth = .1;
ctx.strokeStyle = '#fff';
ctx.moveTo(p.x, p.y);
ctx.lineTo(particles[q].x, particles[q].y);
ctx.stroke();
}
}
// Color
ctx.fillStyle = color;
// Circle path
ctx.beginPath();
ctx.arc(p.x, p.y, p.radius, Math.PI * 2, false);
ctx.fill();
// Lets use the velocity now
p.x += p.vx;
p.y += p.vy;
// If there is only 1 particle
// show X, Y, and velocity
if (num === 1) {
ctx.fillText('Y:'+ p.y, 20, 20);
ctx.fillText('X:'+ p.x, 20, 40);
ctx.fillText('YV:'+ p.vy, 20, 60);
ctx.fillText('XV:'+ p.vx, 20, 80);
}
// To prevent the balls from moving out of the canvas
if (p.x < size) p.vx*= (p.vx / -p.vx);
if (p.y < size) p.vy*= (p.vy / -p.vy);
if (p.x > canvas.width - size) p.vx*= (-p.vx / p.vx);
if (p.y > canvas.height - size) p.vy*= (-p.vy / p.vy);
}
// Loop
requestAnimationFrame(draw);
}
// Function for particle creation
function create_particle() {
// Random position
this.x = Math.random() * canvas.width;
this.y = Math.random() * canvas.height;
// Velocity
this.vx = random_int_between(min_speed, max_speed);
this.vy = random_int_between(min_speed, max_speed);
// Color & Size
this.color = color;
this.radius = size;
}
// Random number between (used for speed)
function random_int_between(min, max) {
return Math.floor(Math.random() * (max-min)) + min;
}
draw();
<canvas id="canvas" width="300" height="300"></canvas>
// Request animation frame
var requestAnimationFrame = window.requestAnimationFrame ||
window.mozRequestAnimationFrame ||
window.webkitRequestAnimationFrame ||
window.msRequestAnimationFrame;
// Canvas
var canvas = document.getElementById('canvas');
var ctx = canvas.getContext('2d');
// Set fullscreen
canvas.width = document.documentElement.clientWidth;
canvas.height = document.documentElement.clientHeight;
// Options
var num =30; // Number of particles to draw
var size = 3; // Particle size
var color = '#fff'; // Particle color
var min_speed = 1; // Particle min speed
var max_speed = 3; // Particle max speed
var line_distance = 20; // This is the max distance between two particles
// if we want to draw a line between them
// Particles array
var particles = [];
for (var i = 0; i < num; i++) {
particles.push(
new create_particle()
);
}
// Lets animate the particle
function draw() {
// Background
ctx.fillStyle = "#000";
ctx.fillRect(0, 0, canvas.width, canvas.height);
// Lets draw particles from the array now
for (var t = 0; t < particles.length; t++) {
// This particle
var p = particles[t];
for (var q = 0; q < particles.length; q++) {
// Check position distance
if (particles[q].x - p.x < line_distance || p.x - particles[q].x < line_distance) {
ctx.beginPath();
ctx.lineWidth = .1;
ctx.strokeStyle = '#fff';
ctx.moveTo(p.x, p.y);
ctx.lineTo(particles[q].x, particles[q].y);
ctx.stroke();
}
}
// Color
ctx.fillStyle = color;
// Circle path
ctx.beginPath();
ctx.arc(p.x, p.y, p.radius, Math.PI * 2, false);
ctx.fill();
// Lets use the velocity now
p.x += p.vx;
p.y += p.vy;
// If there is only 1 particle
// show X, Y, and velocity
if (num === 1) {
ctx.fillText('Y:'+ p.y, 20, 20);
ctx.fillText('X:'+ p.x, 20, 40);
ctx.fillText('YV:'+ p.vy, 20, 60);
ctx.fillText('XV:'+ p.vx, 20, 80);
}
// To prevent the balls from moving out of the canvas
if (p.x < size) p.vx*= (p.vx / -p.vx);
if (p.y < size) p.vy*= (p.vy / -p.vy);
if (p.x > canvas.width - size) p.vx*= (-p.vx / p.vx);
if (p.y > canvas.height - size) p.vy*= (-p.vy / p.vy);
}
// Loop
requestAnimationFrame(draw);
}
// Function for particle creation
function create_particle() {
// Random position
this.x = Math.random() * canvas.width;
this.y = Math.random() * canvas.height;
// Velocity
this.vx = random_int_between(min_speed, max_speed);
this.vy = random_int_between(min_speed, max_speed);
// Color & Size
this.color = color;
this.radius = size;
}
// Random number between (used for speed)
function random_int_between(min, max) {
return Math.floor(Math.random() * max) + min;
}
draw();
<canvas id="canvas"></canvas>
To calculate the distance between two points, you should use pythagoras theorem:
length = sqrt(a² + b²)
Where a is the length of one side, and b is the length of the other side.
var a = (x2 - x1);
var b = (y2 - y1);
var sum = (a * a) + (b * b);
var length = Math.sqrt(sum);
This can be turned into a function, since you know you'll have particles that have an x and y.
function calcLength(particle1, particle2) {
var xDiff = particle2.x - particle1.x;
var yDiff = particle2.y - particle1.y;
var sum = (xDiff * xDiff) + (yDiff * yDiff);
return Math.sqrt(sum);
}
Then you can use that function in your code:
for (var t = 0; t < particles.length; t++) {
var p = particles[t];
for (var q = 0; q < particles.length; q++) {
var p2 = particles[q];
if (calcLength(p, p2) < 20) {
// draw a line between the particles
}
}
}
To calculate the distance between two points you use the pythagorean theorem. http://www.purplemath.com/modules/distform.htm
// Request animation frame
var requestAnimationFrame = window.requestAnimationFrame ||
window.mozRequestAnimationFrame ||
window.webkitRequestAnimationFrame ||
window.msRequestAnimationFrame;
// Canvas
var canvas = document.getElementById('canvas');
var ctx = canvas.getContext('2d');
// Set fullscreen
canvas.width = document.documentElement.clientWidth;
canvas.height = document.documentElement.clientHeight;
// Options
var num =30; // Number of particles to draw
var size = 3; // Particle size
var color = '#fff'; // Particle color
var min_speed = 1; // Particle min speed
var max_speed = 3; // Particle max speed
var line_distance = 20; // This is the max distance between two particles
// if we want to draw a line between them
// Particles array
var particles = [];
for (var i = 0; i < num; i++) {
particles.push(
new create_particle()
);
}
// Lets animate the particle
function draw() {
// Background
ctx.fillStyle = "#000";
ctx.fillRect(0, 0, canvas.width, canvas.height);
// Lets draw particles from the array now
for (var t = 0; t < particles.length; t++) {
// This particle
var p = particles[t];
for (var q = 0; q < particles.length; q++) {
// Check position distance
if (distance(particles[q], p) < line_distance) {
ctx.beginPath();
ctx.lineWidth = 1;
ctx.strokeStyle = '#fff';
ctx.moveTo(p.x, p.y);
ctx.lineTo(particles[q].x, particles[q].y);
ctx.stroke();
}
}
// Color
ctx.fillStyle = color;
// Circle path
ctx.beginPath();
ctx.arc(p.x, p.y, p.radius, Math.PI * 2, false);
ctx.fill();
// Lets use the velocity now
p.x += p.vx;
p.y += p.vy;
// If there is only 1 particle
// show X, Y, and velocity
if (num === 1) {
ctx.fillText('Y:'+ p.y, 20, 20);
ctx.fillText('X:'+ p.x, 20, 40);
ctx.fillText('YV:'+ p.vy, 20, 60);
ctx.fillText('XV:'+ p.vx, 20, 80);
}
// To prevent the balls from moving out of the canvas
if (p.x < size) p.vx*= (p.vx / -p.vx);
if (p.y < size) p.vy*= (p.vy / -p.vy);
if (p.x > canvas.width - size) p.vx*= (-p.vx / p.vx);
if (p.y > canvas.height - size) p.vy*= (-p.vy / p.vy);
}
// Loop
requestAnimationFrame(draw);
}
// Function for particle creation
function create_particle() {
// Random position
this.x = Math.random() * canvas.width;
this.y = Math.random() * canvas.height;
// Velocity
this.vx = random_int_between(min_speed, max_speed);
this.vy = random_int_between(min_speed, max_speed);
// Color & Size
this.color = color;
this.radius = size;
}
// Random number between (used for speed)
function random_int_between(min, max) {
return Math.floor(Math.random() * max) + min;
}
draw();
function distance(pointA, pointB){
var dx = pointB.x - pointA.x;
var dy = pointB.y - pointA.y;
return Math.sqrt(dx*dx + dy*dy);
}
<canvas id="canvas"></canvas>
Please note I increased the lineWidth to 1, so you could see better the result
You have a coordinate system - use the Pythagorean theorem.

Ball Bounce - javascript

function randomXToY(minVal,maxVal,floatVal)
{
var randVal = minVal+(Math.random()*(maxVal-minVal));
return typeof floatVal=='undefined'?Math.round(randVal):randVal.toFixed(floatVal);
}
Ball = (function() {
// constructor
function Ball(x,y,radius,color){
this.center = {x:x, y:y};
this.radius = radius;
this.color = color;
this.dx = 2;
this.dy = 2;
this.boundaryHeight = $('#ground').height();
this.boundaryWidth = $('#ground').width();
this.dom = $('<p class="circle"></p>').appendTo('#ground');
// the rectange div a circle
this.dom.width(radius*2);
this.dom.height(radius*2);
this.dom.css({'border-radius':radius,background:color});
this.placeAtCenter(x,y);
}
// Place the ball at center x, y
Ball.prototype.placeAtCenter = function(x,y){
this.dom.css({top: Math.round(y- this.radius), left: Math.round(x - this.radius)});
this.center.x = Math.round(x);
this.center.y = Math.round(y);
};
Ball.prototype.setColor = function(color) {
if(color) {
this.dom.css('background',color);
} else {
this.dom.css('background',this.color);
}
};
// move and bounce the ball
Ball.prototype.move = function(){
var diameter = this.radius * 2;
var radius = this.radius;
if (this.center.x - radius < 0 || this.center.x + radius > this.boundaryWidth ) {
this.dx = -this.dx;
}
if (this.center.y - radius < 0 || this.center.y + radius > this.boundaryHeight ) {
this.dy = -this.dy;
}
this.placeAtCenter(this.center.x + this.dx ,this.center.y +this.dy);
};
return Ball;
})();
var number_of_balls = 5;
var balls = [];
$('document').ready(function(){
for (i = 0; i < number_of_balls; i++) {
var boundaryHeight = $('#ground').height();
var boundaryWidth = $('#ground').width();
var y = randomXToY(30,boundaryHeight - 50);
var x = randomXToY(30,boundaryWidth - 50);
var radius = randomXToY(15,30);
balls.push(new Ball(x,y,radius, '#'+Math.floor(Math.random()*16777215).toString(16)));
}
loop();
});
loop = function(){
for (var i = 0; i < balls.length; i++){
balls[i].move();
}
setTimeout(loop, 8);
};
I have never used in oops concepts in javascript. How do I change the ball color when the balls touches each other?
This is the link : http://jsbin.com/imofat/1/edit
You currently don't have any interaction with the balls. What you can do is checking whether two balls are "inside" each other, and change colors in that case: http://jsbin.com/imofat/1491/.
// calculates distance between two balls
var d = function(a, b) {
var dx = b.center.x - a.center.x;
var dy = b.center.y - a.center.y;
return Math.sqrt(dx*dx + dy*dy);
};
and:
// for each ball
for(var i = 0; i < balls.length; i++) {
// check against rest of balls
for(var j = i + 1; j < balls.length; j++) {
var a = balls[i];
var b = balls[j];
// distance is smaller than their radii, so they are inside each other
if(d(a, b) < a.radius + b.radius) {
// set to some other color using your random color code
a.setColor('#'+Math.floor(Math.random()*16777215).toString(16));
b.setColor('#'+Math.floor(Math.random()*16777215).toString(16));
}
}
}
Still, there are things for improvement:
Balls are changing colors as long as they are inside each other, not just once.
If you want them to "touch", you might want to implement some kind of bouncing effect to make it more realistic.

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