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I'm trying to make a ball jump even in midair, but my code always just teleports to the same spot and then jumps, can anydody tell me how to fix this problem of mine? It needs to be able to jump wherever it is at that exact moment, and i've already tried something with set interval.
I'm trying to make a ball jump even in midair, but my code always just teleports to the same spot and then jumps, can anydody tell me how to fix this problem of mine? It needs to be able to jump wherever it is at that exact moment, and i've already tried something with set interval.
I'm trying to make a ball jump even in midair, but my code always just teleports to the same spot and then jumps, can anydody tell me how to fix this problem of mine? It needs to be able to jump wherever it is at that exact moment, and i've already tried something with set interval.
var canvas, ctx, container;
canvas = document.createElement('canvas');
ctx = canvas.getContext("2d");
var ball;
var touchGround = false;
var pull= 0.43;
var vy;
var gravity = pull;
var i = Math.floor(Math.random()*11)
color = ["red", "blue","green","yellow","purple","white","pink","silver","teal","turqu oise","magenta","cyan"];
console.log(color[i])
function ballMovement() {
vy += gravity;
ball.y += vy;
if (ball.y + ball.radius > canvas.height) {
ball.y = canvas.height - ball.radius;
vy = 0;
var img = document.getElementById('gameOver');
ctx.drawImage(gameOver, canvas.width/2-436, 100)
ball.radius = 0;
}
}
function init() {
setupCanvas();
var img = document.getElementById('gameOver');
img.style.visibility = 'hidden';
//how high the ball goes
vy = -19;
var y1 = 450
ball = {
x: canvas.width/2,
//where the ball starts moving upwards
y: 480, //here1
radius: 20,
status: 0,
color: color[i]};
}
function draw() {
ctx.clearRect(0, 0, canvas.width, canvas.height);
ctx.beginPath();
ctx.arc(ball.x, ball.y, ball.radius, 0, Math.PI * 2, false);
ctx.fillStyle = ball.color;
ctx.fill();
ctx.closePath()
//draw a moving ball
ballMovement();
}
setInterval(draw, 1000 / 35);
function setupCanvas() {
container = document.createElement('div');
container.className = "container";
canvas.width = window.innerWidth;
canvas.height = window.innerHeight;
document.body.appendChild(container);
container.appendChild(canvas);
ctx.strokeStyle = "#ffffff";
ctx.lineWidth = 2;
}
window.onclick = function(jump){
pull + 0.1;
touchGround = false;
init()
draw()
ballMovement()
setupCanvas()
vy+((canvas.height-canvas.height)-ball.y);
}
//GOAL
//Ball jumps at somewhere in screen, let it jump wherever it is.
If I got you correctly you want your ball to go higher and higher. But problem is that you got fixed position where it's starts so where's what you need to change:
var canvas, ctx, container;
canvas = document.createElement('canvas');
canvas.width = 800;
canvas.height = 800;
ctx = canvas.getContext("2d");
var ball = {
y: 480
};
var touchGround = false;
var pull= 0.43;
var vy;
var gravity = pull;
//Creating a variable to know whether our game is running
var gameRunning = 0;
var i = Math.floor(Math.random()*11);
//Adding variable for interval so we can start it with init function
var timer;
color = ["red", "blue","green","yellow","purple","pink","silver","teal","turquoise","magenta","cyan", "black"];
function ballMovement() {
vy += gravity;
ball.y += vy;
if (ball.y + ball.radius > canvas.height) {
ball.y = canvas.height - ball.radius;
vy = 0;
var img = document.getElementById('gameOver');
ctx.drawImage(gameOver, canvas.width/2-436, 100)
ball.radius = 0;
//Stoping the draw function
clearInterval(timer);
//Saying the game isn't running
gameRunning = 0;
}
}
function init() {
//Check if canvas already created
if(!document.querySelector('.container')){
setupCanvas()
}
vy = -19;
var y1 = 450
ball = {
x: canvas.width/2,
y: ball.y,
radius: 20,
status: 0,
color: color[i]
};
//Clearing previous interval if it were any and creating a new one
clearInterval(timer);
timer = setInterval(draw, 1000 / 60);
//Saying the game is running
gameRunning = 1;
}
function draw() {
ctx.clearRect(0, 0, canvas.width, canvas.height);
ctx.beginPath();
ctx.arc(ball.x, ball.y, ball.radius, 0, Math.PI * 2, false);
ctx.fillStyle = ball.color;
ctx.fill();
ctx.closePath()
ballMovement();
}
function setupCanvas() {
container = document.createElement('div');
container.className = "container";
canvas.width = window.innerWidth;
canvas.height = window.innerHeight;
document.body.appendChild(container);
container.appendChild(canvas);
ctx.strokeStyle = "#ffffff";
ctx.lineWidth = 2;
}
window.onclick = function(){
pull + 0.1;
touchGround = false;
//Check if the game is running or not
//If it's not running - call init
if(!gameRunning){
init();
}
else{
//If game is already running - change speed
vy = -19;
}
//I've also removed some function that were starting with init itself
vy+((canvas.height-canvas.height)-ball.y);
}
Please check out this code :
(function() {
var cnv = document.getElementById('canvas');
if (cnv.getContext) {
var ctx = cnv.getContext('2d');
} else {
alert('God Damn it ...');
}
function initialize() {
window.addEventListener('resize', resizeCanvas, false);
resizeCanvas();
}
function draw() {
for (var i = 0; i < 25; i++) {
width = Math.random() * cnv.width;
height = Math.random() * cnv.height;
ctx.beginPath();
ctx.arc(width, height, 15, 0, Math.PI * 2);
ctx.strokeStyle = '#E1E1E1';
ctx.lineWidth = 1;
ctx.stroke();
}
}
function resizeCanvas() {
cnv.width = window.innerWidth;
cnv.height = window.innerHeight;
draw();
}
initialize();
})();
I have created 25 Circle shape with random position and I want to create an animation that scales up or down in a interval time. I know about setInterval but how should I call my shape to do something on it?
The first thing you will want to do is to have a place to store the position of your circles, since they are all going to be the same radius we can just store the x and y position. For that we can create a Circle function ("class") and have an array of circles:
var circles = []; // Array to store our circles
var minRadius = 1; // The smallest radius we can hit
var maxRadius = 100; // The largest radius we can hit
var currentRadius = 15;// The current radius of all our circles
var scaleBy = 1; // How the radius changes
var cnv = document.getElementById('canvas');
// ...
function initialize() {
window.addEventListener('resize', resizeCanvas, false);
resizeCanvas();
// Populating the array of circles to use when drawing
for (var i = 0; i < 25; i++) { // Make sure to do this after re-sizing the canvas
width = Math.random() * cnv.width;
height = Math.random() * cnv.height;
circles.push(new Circle(width, height));
}
}
// ...
function Circle(x, y){
this.x = x;
this.y = y;
}
Circle.prototype.draw = function(){
ctx.beginPath();
ctx.arc(this.x, this.y, currentRadius, 0, Math.PI * 2);
ctx.strokeStyle = '#E1E1E1';
ctx.lineWidth = 5;
ctx.stroke();
}
Now that you have some circles when you call draw you can iterate through the array and call circle.draw() for each circle element in your array:
function draw() {
// Clear the screen and draw the circles in our array
ctx.clearRect(0,0, cnv.width, cnv.height);
for (var i = 0; i < circles.length; i++) {
circles[i].draw();
}
}
One note is you will want to use ctx.clearRect(0,0, cnv.width, cnv.height) to clear the screen before drawing.
Finally you can now use setInterval to change the currentRadius (*While there is nothing wrong with setInterval I'd recommend using window.requestAnimationFrame for animation as it's a bit more smooth and efficient method). Then when you call draw it will draw the circles with the new value of currentRadius. In this example I'm going to have it start at 15. Then increase by 1 until it hits maxRadius, then we can flip the sign of scaleBy to start decreasing the radius to make them smaller. Finally when it his our minRadius you can flip the sign of scaleBy again to make it start scaling up again:
var timer = setInterval( function(){
// If we hit our min or max start scaling in the other direction
if(currentRadius > maxRadius || currentRadius < minRadius){
scaleBy *= -1;
}
currentRadius += scaleBy;
draw();
}, 50);
Below is a code snippet of the complete program:
(function() {
var circles = [];
var minRadius = 1;
var maxRadius = 100;
var currentRadius = 15;
var scaleBy = 1;
var cnv = document.getElementById('canvas');
if (cnv.getContext) {
var ctx = cnv.getContext('2d');
} else {
alert('God Damn it ...');
}
function initialize() {
window.addEventListener('resize', resizeCanvas, false);
resizeCanvas();
for (var i = 0; i < 25; i++) {
width = Math.random() * cnv.width;
height = Math.random() * cnv.height;
circles.push(new Circle(width, height));
}
}
function draw() {
ctx.clearRect(0,0, cnv.width, cnv.height);
for (var i = 0; i < circles.length; i++) {
circles[i].draw();
}
}
function resizeCanvas() {
cnv.width = window.innerWidth;
cnv.height = window.innerHeight;
}
function Circle(x, y){
this.x = x;
this.y = y;
}
Circle.prototype.draw = function(){
ctx.beginPath();
ctx.arc(this.x, this.y, currentRadius, 0, Math.PI * 2);
ctx.strokeStyle = '#E1E1E1';
ctx.lineWidth = 5;
ctx.stroke();
}
initialize();
var timer = setInterval( function(){
if(currentRadius > maxRadius || currentRadius < minRadius){
scaleBy *= -1;
}
currentRadius += scaleBy;
draw();
}, 50);
})();
<canvas id="canvas"></canvas>
I'm attempting to draw the rotating line in this canvas animation with trailing opacity but it's not working. I've seen this effect with rectangles and arcs but never with a line, so I'm not sure what I need to add.
function radians(degrees) {
return degrees * (Math.PI / 180);
}
var timer = 0;
function sonar() {
var canvas = document.getElementById('sonar');
if (canvas) {
var ctx = canvas.getContext('2d');
var cx = innerWidth / 2,
cy = innerHeight / 2;
canvas.width = innerWidth;
canvas.height = innerHeight;
//ctx.clearRect(0, 0, innerWidth, innerHeight);
ctx.fillStyle = 'rgba(255, 255, 255, 0.5)';
ctx.fillRect(0, 0, innerWidth, innerHeight);
var radii = [cy, cy - 30, innerHeight / 3.33, innerHeight / 6.67];
for (var a = 0; a < 4; a++) {
ctx.beginPath();
ctx.arc(cx, cy, radii[a], radians(0), radians(360), false);
ctx.strokeStyle = 'limegreen';
ctx.stroke();
ctx.closePath();
}
// draw grid lines
for (var i = 0; i < 12; i++) {
var x = cx + cy * Math.cos(radians(i * 30));
var y = cy + cy * Math.sin(radians(i * 30));
ctx.beginPath();
ctx.moveTo(cx, cy);
ctx.lineTo(x, y);
ctx.lineCap = 'round';
ctx.strokeStyle = 'rgba(50, 205, 50, 0.45)';
ctx.stroke();
ctx.closePath();
}
if (timer <= 360) {
timer++;
ctx.beginPath();
ctx.fillstyle = 'limegreen';
ctx.moveTo(cx, cy);
ctx.lineTo(cx + cy * Math.cos(radians(timer)), cy + cy * Math.sin(radians(timer)));
ctx.strokeStyle = 'limegreen';
ctx.stroke();
ctx.closePath();
} else {
timer = 0;
}
requestAnimationFrame(sonar);
}
}
sonar();
jsbin example
Here are two ways to do this: with a gradient and by adding translucent lines.
Sidenote, you should try and only redraw what you need to redraw. I separated the canvases and put one on top of the other so that we don't redraw the grid all the time.
function radians(degrees) {
return degrees * (Math.PI / 180);
}
var timer = 0;
function trail() {
var canvas = document.getElementById('trail');
var ctx = canvas.getContext('2d');
ctx.clearRect(0, 0, innerWidth, innerHeight);
var cx = innerWidth / 2,
cy = innerHeight / 2;
canvas.width = innerWidth;
canvas.height = innerHeight;
if (timer <= 360) {
timer++;
ctx.beginPath();
ctx.fillstyle = 'limegreen';
ctx.moveTo(cx, cy);
ctx.arc(cx,cy,cy,radians(timer-30),radians(timer));
ctx.lineTo(cx + cy * Math.cos(radians(timer)), cy + cy * Math.sin(radians(timer)));
var gradient = ctx.createLinearGradient(
cx+cy*Math.cos(radians(timer)), cy+cy*Math.sin(radians(timer)),
cx+cy*0.9*Math.cos(radians(timer-30)), cy+cy*0.9*Math.sin(radians(timer-30)));
gradient.addColorStop(0,'limegreen');
gradient.addColorStop(1,'transparent');
ctx.strokeStyle='transparent';
ctx.fillStyle = gradient;
ctx.fill();
ctx.beginPath();
var fade = 10;
for(var i =0;i<fade;i++)
{
ctx.moveTo(cx, cy);
ctx.lineTo(cx+cy*Math.cos(radians(180+timer-i*1.3)),cy+cy*Math.sin(radians(180+timer-i*1.3)));
ctx.strokeStyle ="rgba(50,205,50,0.1)";
ctx.lineWidth=5;
ctx.closePath();
ctx.stroke();
}
} else {
timer = 0;
}
requestAnimationFrame(trail);
}
function sonar() {
var canvas = document.getElementById('sonar');
if (canvas) {
var ctx = canvas.getContext('2d');
var cx = innerWidth / 2,
cy = innerHeight / 2;
canvas.width = innerWidth;
canvas.height = innerHeight;
//ctx.clearRect(0, 0, innerWidth, innerHeight);
var radii = [cy, cy - 30, innerHeight / 3.33, innerHeight / 6.67];
for (var a = 0; a < 4; a++) {
ctx.beginPath();
ctx.arc(cx, cy, radii[a], radians(0), radians(360), false);
ctx.strokeStyle = 'limegreen';
ctx.stroke();
ctx.closePath();
}
// draw grid lines
for (var i = 0; i < 12; i++) {
var x = cx + cy * Math.cos(radians(i * 30));
var y = cy + cy * Math.sin(radians(i * 30));
ctx.beginPath();
ctx.moveTo(cx, cy);
ctx.lineTo(x, y);
ctx.lineCap = 'round';
ctx.strokeStyle = 'rgba(50, 205, 50, 0.45)';
ctx.stroke();
ctx.closePath();
}
}
}
sonar();
trail();
canvas{
position: absolute;
}
<canvas id=sonar></canvas>
<canvas id=trail></canvas>
The problem is that to get this effect, you need to draw a triangle with a gradient along an arc, and you can't do that in a canvas. Gradients must be linear or radial.
The other option is to have an inner loop run each time you want to draw the sweeper, and go backwards from your sweeper line, drawing with slightly less opacity each time. But lets say you want your sweep to cover 15 degrees--obviously, if you have a 100% opacity line at d and a 5% opacity line at d - 15, that doesn't do the trick. So start filling in more lines, and more lines...you will have to draw so many lines to make it seem filled your performance would probably suffer.
My suggestion--you shouldn't have to redraw that on every frame. I would just make a PNG that looks like you want it to, and then place it and just rotate it around the center on each frame. No need to redraw it all the time then. That will be much faster than drawing a bunch of lines.
Canvas stack trails.
Below is a quick demo of how to use a stack of canvases to create a trailing effect.
You have a normal on screen canvas (this FX will not effect it) and then a stack of canvases for the trail FX. Each frame you move to the next canvas in the stack, first slightly clearing it then drawing to it what you want to trail. Then you render that canvas and the one just above it to the canvas.
A point to keep in mind is that the trails can also have a hugh range of FX, like blurring (just render each frame stack on itself slightly offset each time you render to it), zoom in and out trails. Trails on top or trails under. You can change the trail distance and much more.
It is overkill but over kill is fun.
The slider above the demo controls the trail length. Also the code need babel because I dont have time to write it for ES5.
Top slider is trail amount.One under that is trail distance. Trail dist does not transition well. Sorry about that.
//==============================================================================
// helper function
function $(query,q1){
if(q1 !== undefined){
if(typeof query === "string"){
var e = document.createElement(query);
if(typeof q1 !== "string"){
for(var i in q1){
e[i] = q1[i];
}
}else{
e.id = q1;
}
return e;
}
return [...query.querySelectorAll(q1)];
}
return [...document.querySelectorAll(query)];
}
function $$(element,e1){
if(e1 !== undefined){
if(typeof element === "string"){
$(element)[0].appendChild(e1);
return e1;
}
element.appendChild(e1);
return e1;
}
document.body.appendChild(element);
return element;
}
function $E(element,types,listener){
if(typeof types === "string"){
types = types.split(",");
}
element = $(element)[0];
types.forEach(t=>{
element.addEventListener(t,listener)
});
return element;
}
function R(I){
if(I === undefined){
return Math.random();
}
return Math.floor(Math.random()*I);
}
//==============================================================================
//==============================================================================
// answer code
// canvas size
const size = 512;
const trailDist = 10; // There is this many canvases so be careful
var trailDistCurrent = 10; // distance between trails
var clearAll = false;
// create a range slider for trail fade
$$($("input",{type:"range",width : size, min:0, max:100, step:0.1, value:50, id:"trail-amount",title:"Trail amount"}));
$("#trail-amount")[0].style.width = size + "px";
$E("#trail-amount","change,mousemove",function(e){fadeAmount = Math.pow(this.value / 100,2);});
// create a range slider trail distance
$$($("input",{type:"range",width : size, min:2, max:trailDist , step:1, value:trailDist , id:"trail-dist",title:"Trail seperation"}));
$("#trail-dist")[0].style.width = size + "px";
$E("#trail-dist","change,mousemove", function(e){
if(this.value !== trailDistCurrent){
trailDistCurrent= this.value;
clearAll = true;
}
});
$$($("br","")) // put canvas under the slider
// Main canvas
var canvas;
$$(canvas = $("canvas",{width:size,height:size})); // Not jquery. Just creates a canvas
// and adds canvas to the document
var ctx = canvas.getContext("2d");
// Trailing canvas
var trailCanvases=[];
var i =0; // create trail canvas
while(i++ < trailDist){trailCanvases.push($("canvas",{width:size,height:size}));}
var ctxT = trailCanvases.map(c=>c.getContext("2d")); // get context
var topCanvas = 0;
var fadeAmount = 0.5;
// Draw a shape
function drawShape(ctx,shape){
ctx.lineWidth = shape.width;
ctx.lineJoin = "round";
ctx.strokeStyle = shape.color;
ctx.setTransform(shape.scale,0,0,shape.scale,shape.x,shape.y);
ctx.rotate(shape.rot);
ctx.beginPath();
var i = 0;
ctx.moveTo(shape.shape[i++],shape.shape[i++]);
while(i < shape.shape.length){
ctx.lineTo(shape.shape[i++],shape.shape[i++]);
}
ctx.stroke();
}
// Create some random shapes
var shapes = (function(){
function createRandomShape(){
var s = [];
var len = Math.floor(Math.random()*5 +4)*2;
while(len--){
s[s.length] = (R() + R()) * 20 * (R() < 0.5 ? -1 : 1);
}
return s;
}
var ss = [];
var i = 10;
while(i--){
ss[ss.length] = createRandomShape();
}
ss[ss.length] = [0,0,300,0]; // create single line
return ss;
})();
// Create some random poits to move the shapes
var points = (function(){
function point(){
return {
color : "hsl("+R(360)+",100%,50%)",
shape : shapes[R(shapes.length)],
width : R(4)+1,
x : R(size),
y : R(size),
scaleMax : R()*0.2 + 1,
scale : 1,
s : 0,
rot : R()*Math.PI * 2,
dr : R()*0.2 -0.1,
dx : R()*2 - 1,
dy : R()*2 - 1,
ds : R() *0.02 + 0.01,
}
}
var line = shapes.pop();
var ss = [];
var i = 5;
while(i--){
ss[ss.length] = point();
}
var s = ss.pop();
s.color = "#0F0";
s.x = s.y = size /2;
s.dx = s.dy = s.ds = 0;
s.scaleMax = 0.5;
s.dr = 0.02;
s.shape = line;
s.width = 6;
ss.push(s);
return ss;
})();
var frameCount = 0; // used to do increamental fades for long trails
function update(){
// to fix the trail distance problem when fade is low and distance high
if(clearAll){
ctxT.forEach(c=>{
c.setTransform(1,0,0,1,0,0);
c.clearRect(0,0,size,size);
});
clearAll = false;
}
frameCount += 1;
// get the next canvas that the shapes are drawn to.
topCanvas += 1;
topCanvas %= trailDistCurrent;
var ctxTop = ctxT[topCanvas];
// clear the main canvas
ctx.setTransform(1,0,0,1,0,0); // reset transforms
// Fade the trail canvas
ctxTop.setTransform(1,0,0,1,0,0);
ctx.clearRect(0,0,size,size); // clear main canvas
// slowly blendout trailing layer
if(fadeAmount < 0.1){ // fading much less than this leaves perminant trails
// so at low levels just reduce how often the fade is done
if(((Math.floor(frameCount/trailDistCurrent)+topCanvas) % Math.ceil(1 / (fadeAmount * 10))) === 0 ){
ctxTop.globalAlpha = 0.1;
ctxTop.globalCompositeOperation = "destination-out";
ctxTop.fillRect(0,0,size,size);
}
}else{
ctxTop.globalAlpha = fadeAmount;
ctxTop.globalCompositeOperation = "destination-out";
ctxTop.fillRect(0,0,size,size);
}
ctxTop.globalCompositeOperation = "source-over";
ctxTop.globalAlpha = 1;
// draw shapes
for(var i = 0; i < points.length; i ++){
var p = points[i];
p.x += p.dx; // move the point
p.y += p.dy;
p.rot += p.dr;
p.s += p.ds;
p.dr += Math.sin(p.s) * 0.001;
p.scale = Math.sin(p.s) * p.scaleMax+1;
p.x = ((p.x % size) + size) % size;
p.y = ((p.y % size) + size) % size;
drawShape(ctxTop,p); // draw trailing layer (middle)
}
// draw the trail the most distance from the current position
ctx.drawImage(trailCanvases[(topCanvas + 1)%trailDistCurrent],0,0);
// do it all again.
requestAnimationFrame(update);
}
update();
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.
I'm trying to set up a background in canvas and have some small circles just flow throughout the background, eventually I'll change the shapes and add more details in, but I'm just having trouble with the set up.
I know my code is janky, but are there any suggestions to the structure of the code?
var dx = 1;
var dy = 2;
var circle=new Circle(400,30,10);
var timer;
function Circle(x,y,r){
this.x=x;
this.y=y;
this.r=r;
}
function init() {
// Get the canvas element.
canvas = document.getElementById("canvas");
if (canvas.getContext) {
ctx = canvas.getContext("2d");
ctx.fillStyle = "black";
}
timer=setInterval(draw, 10);
return timer;
}
function gradient (){
var my_gradient=ctx.createLinearGradient(0,0,1000,0);
my_gradient.addColorStop(0,"black");
my_gradient.addColorStop(1,"white");
ctx.fillStyle=my_gradient;
ctx.fillRect(0,0,1000,1000);
ctx.rect(0, 0, 1000, 1000);
stars();
}
function stars(){
for (i = 0; i <= 50; i++) {
// Get random positions for stars
var x = Math.floor(Math.random() * 1000)
var y = Math.floor(Math.random() * 1000)
ctx.fillStyle = "yellow";
//if (x < 30 || y < 30) ctx.fillStyle = "black";
ctx.beginPath();
ctx.arc(x, y, 3, 0, Math.PI * 2, true);
ctx.closePath();
ctx.fill();
}
}
function move(){
ctx.clearRect(0, 0, canvas.width, canvas.height);
ctx.fillStyle = gradient.my_gradient;
ctx.fillRect(0,0,canvas.width,canvas.height);
ctx.fillStyle = "#003300";
drawBall(circle);
if (circle.x +dx > canvas.width || circle.x +dx < 0)
dx=-dx;
if(circle.y+dy>bar.y && circle.x>bar.x && circle.x<bar.x+barImg.width)
dy=-dy;
if (circle.y +dy > canvas.height || circle.y +dy < 0)
dy=-dy;
circle.x += dx;
circle.y += dy;
}
I tried to code a working exemple. Here stars are popping up continuously.
HTML
<!DOCTYPE html>
<html>
<head>
<title>Exemple</title>
</head>
<body>
<canvas id="viewport"></canvas>
<script src='test.js'></script>
</body>
</html>
JS
var doc = document;
var canvas = doc.getElementById('viewport');
var ctx = canvas.getContext('2d');
var settings = {
area : {
height : 100,
width : 100
}
};
canvas.width = settings.area.width;
canvas.height = settings.area.height;
function draw() {
for (var i = 10; i--;) {
var x = Math.floor(Math.random() * 1000)
var y = Math.floor(Math.random() * 1000)
ctx.beginPath();
ctx.arc(x, y, 3, 0, Math.PI * 2, true);
ctx.fillStyle = "yellow";
ctx.closePath();
ctx.fill();
}
}
function gameLoop (render, element) {
var running, lastFrame = +new Date;
function loop( now ) {
// stop the loop if render returned false
if ( running !== false ) {
requestAnimationFrame( loop, element );
running = render( now - lastFrame );
lastFrame = now;
}
}
loop( lastFrame );
}
gameLoop (function (deltaT) {
draw();
}, canvas );
Here is the fiddle : https://jsfiddle.net/q4q0uLht/
----- EDIT -----
/*
Basic config
*/
var doc = document,
canvas = doc.getElementById('viewport'),
ctx = canvas.getContext('2d');
var settings = {
canvas: {
height: 200,
width: 300
}
}
canvas.height = settings.canvas.height;
canvas.width = settings.canvas.width;
canvas.style.border = '1px #000 solid';
/*
easy gets a random number, inside a range of [0, x);
*/
function getRandomNumber(x) {
return parseInt(Math.random() * x, 10);
}
/*
Checks if the obj passed in argument is still in the canvas limits
*/
function incorrectPosition(obj) {
return obj.x < 0 || obj.y < 0 || obj.x > settings.canvas.width || obj.y > settings.canvas.height;
}
/*
stars array and Star object.
*/
var stars = [];
function Star(r) {
this.x = getRandomNumber(canvas.width);
this.y = getRandomNumber(canvas.height);
this.r = r || 10;
this.move = function(dx, dy) {
this.x += dx;
this.y += dy;
};
}
/*
This function adds new stars,
calculates new coordinates of each star,
and removes them from the stars array
when they are out of the canvas limits.
*/
function update() {
var len = stars.length;
if (len < 10) {
stars.push(new Star());
}
for (var i = len; i--;) {
var star = stars[i];
star.move(1, 2);
if (incorrectPosition(star)) {
stars.splice(i, 1);
}
}
}
/*
This function clears the canvas each turn and
draws each star which is stored inside the stores array.
*/
function draw() {
ctx.clearRect(0, 0, settings.canvas.width, settings.canvas.height);
var len = stars.length;
for (var i = len; i--;) {
var star = stars[i];
ctx.beginPath();
ctx.arc(star.x, star.y, 3, 0, Math.PI * 2, true);
ctx.fillStyle = "yellow";
ctx.closePath();
ctx.fill();
}
}
// Here is the loop inside which are called functions
setInterval(loop, 33);
function loop() {
update(); // update first
draw(); // then draw
}
<!DOCTYPE html>
<html>
<head>
<title>Exemple</title>
</head>
<body>
<canvas id="viewport"></canvas>
<script src='test.js'></script>
</body>
</html>