moving an image across a html canvas - html

I am trying to move an image from the right to the center and I am not sure if this is the best way.
var imgTag = null;
var x = 0;
var y = 0;
var id;
function doCanvas()
{
var canvas = document.getElementById('icanvas');
var ctx = canvas.getContext("2d");
var imgBkg = document.getElementById('imgBkg');
imgTag = document.getElementById('imgTag');
ctx.drawImage(imgBkg, 0, 0);
x = canvas.width;
y = 40;
id = setInterval(moveImg, 0.25);
}
function moveImg()
{
if(x <= 250)
clearInterval(id);
var canvas = document.getElementById('icanvas');
var ctx = canvas.getContext("2d");
ctx.clearRect(0, 0, canvas.width, canvas.height);
var imgBkg = document.getElementById('imgBkg');
ctx.drawImage(imgBkg, 0, 0);
ctx.drawImage(imgTag, x, y);
x = x - 1;
}
Any advice?

This question is 5 years old, but since we now have requestAnimationFrame() method, here's an approach for that using vanilla JavaScript:
var imgTag = new Image(),
canvas = document.getElementById('icanvas'),
ctx = canvas.getContext("2d"),
x = canvas.width,
y = 0;
imgTag.onload = animate;
imgTag.src = "http://i.stack.imgur.com/Rk0DW.png"; // load image
function animate() {
ctx.clearRect(0, 0, canvas.width, canvas.height); // clear canvas
ctx.drawImage(imgTag, x, y); // draw image at current position
x -= 4;
if (x > 250) requestAnimationFrame(animate) // loop
}
<canvas id="icanvas" width=640 height=180></canvas>

drawImage() enables to define which part of the source image to draw on target canvas. I would suggest for each moveImg() calculate the previous image position, overwrite the previous image with that part of imgBkg, then draw the new image. Supposedly this will save some computing power.

Here's my answer.
var canvas = document.getElementById("canvas");
ctx = canvas.getContext("2d");
var myImg = new Image();
var myImgPos = {
x: 250,
y: 125,
width: 50,
height: 25
}
function draw() {
myImg.onload = function() {
ctx.drawImage(myImg, myImgPos.x, myImgPos.y, myImgPos.width, myImgPos.height);
}
myImg.src = "https://mario.wiki.gallery/images/thumb/c/cc/NSMBUD_Mariojump.png/1200px-NSMBUD_Mariojump.png";
}
function moveMyImg() {
ctx.clearRect(myImgPos.x, myImgPos.y, myImgPos.x + myImgPos.width, myImgPos.y +
myImgPos.height);
myImgPos.x -= 5;
}
setInterval(draw, 50);
setInterval(moveMyImg, 50);
<canvas id="canvas" class="canvas" width="250" height="150"></canvas>

For lag free animations,i generally use kinetic.js.
var stage = new Kinetic.Stage({
container: 'container',
width: 578,
height: 200
});
var layer = new Kinetic.Layer();
var hexagon = new Kinetic.RegularPolygon({
x: stage.width()/2,
y: stage.height()/2,
sides: 6,
radius: 70,
fill: 'red',
stroke: 'black',
strokeWidth: 4
});
layer.add(hexagon);
stage.add(layer);
var amplitude = 150;
var period = 2000;
// in ms
var centerX = stage.width()/2;
var anim = new Kinetic.Animation(function(frame) {
hexagon.setX(amplitude * Math.sin(frame.time * 2 * Math.PI / period) + centerX);
}, layer);
anim.start();
Here's the example,if you wanna take a look.
http://www.html5canvastutorials.com/kineticjs/html5-canvas-kineticjs-animate-position-tutorial/
Why i suggest this is because,setInterval or setTimeout a particular function causes issues when large amount of simultaneous animations take place,but kinetic.Animation deals with framerates more intelligently.

Explaining window.requestAnimationFrame() with an example
In the following snippet I'm using an image for the piece that is going to be animated.
I'll be honest... window.requestAnimationFrame() wasn't easy for me to understand, that is why I coded it as clear and intuitive as possible. So that you may struggle less than I did to get my head around it.
const
canvas = document.getElementById('root'),
btn = document.getElementById('btn'),
ctx = canvas.getContext('2d'),
brickImage = new Image(),
piece = {image: brickImage, x:400, y:70, width:70};
brickImage.src = "https://i.stack.imgur.com/YreH6.png";
// When btn is clicked execute start()
btn.addEventListener('click', start)
function start(){
btn.value = 'animation started'
// Start gameLoop()
brickImage.onload = window.requestAnimationFrame(gameLoop)
}
function gameLoop(){
// Clear canvas
ctx.clearRect(0, 0, canvas.width, canvas.height)
// Draw at coordinates x and y
ctx.drawImage(piece.image, piece.x, piece.y)
let pieceLeftSidePos = piece.x;
let middlePos = canvas.width/2 - piece.width/2;
// Brick stops when it gets to the middle of the canvas
if(pieceLeftSidePos > middlePos) piece.x -= 2;
window.requestAnimationFrame(gameLoop) // Needed to keep looping
}
<input id="btn" type="button" value="start" />
<p>
<canvas id="root" width="400" style="border:1px solid grey">
A key point
Inside the start() function we have:
brickImage.onload = window.requestAnimationFrame(gameLoop);
This could also be written like: window.requestAnimationFrame(gameLoop);
and it would probably work, but I'm adding the brickImage.onload to make sure that the image has loaded first. If not it could cause some issues.
Note: window.requestAnimationFrame() usually loops at 60 times per second.

Related

HTML Canvas to WPF XAML Canvas

I have an ASP.NET application that allows users to click or tap on a Canvas to indicate pain locations on a body image. A body image is displayed on the Canvas and is the same size as the Canvas.
function drawBodyMap() {
var c = document.getElementById('myCanvas');
var ctx = c.getContext('2d');
var imageObj = new Image();
imageObj.src = 'https://.../body.jpg';
imageObj.onload = function () {
ctx.drawImage(imageObj, 0, 0, 600, 367);
};
}
<canvas id="myCanvas" width="600" height="367"></canvas>
<script>
function getMousePos(canvas, evt) {
var rect = canvas.getBoundingClientRect();
return {
x: evt.clientX - rect.left,
y: evt.clientY - rect.top
};
}
var canvas = document.getElementById('myCanvas');
var ctx = canvas.getContext('2d');
canvas.addEventListener('mouseup', function (evt) {
if (ixPos > 9)
return;
var mousePos = getMousePos(canvas, evt);
bodyX[ixPos] = mousePos.x;
bodyY[ixPos] = mousePos.y;
painType[ixPos] = pain_type;
ixPos++;
ctx.beginPath();
ctx.arc(mousePos.x, mousePos.y, 8, 0, 2 * Math.PI);
if (pain_type == 1)
ctx.fillStyle = "#DC143C";
else if (pain_type == 2)
ctx.fillStyle = "#EA728A";
else if (pain_type == 3)
ctx.fillStyle = "#DAA520";
else if (pain_type == 4)
ctx.fillStyle = "#008000";
else if (pain_type == 5)
ctx.fillStyle = "#4169E1";
ctx.fill();
}, false);
</script>
The X,Y points added to the Canvas on the body image are saved to a database. These points are then loaded into a WPF application that displays the same body image on an XAML Canvas. C# code then adds the points over the image.
WPF CODE:
private void DisplayBodyPain()
{
List<BodyPain> pain = gFunc.sws.GetBodyPain(MemberID);
foreach (BodyPain bp in pain)
{
Border b = new Border();
b.Tag = bp.PainType.ToString();
b.Cursor = Cursors.Hand;
b.Width = 16;
b.Height = 16;
b.CornerRadius = new CornerRadius(8);
b.Background = GetPainBrush((byte)bp.PainType);
cvsBody.Children.Add(b);
Canvas.SetTop(b, bp.YPos);
Canvas.SetLeft(b, bp.XPos);
}
}
The problem I have is that the points drawn on the XAML Canvas are all slightly different from the points that were drawn on the HTML Canvas. Each point is not in exactly the same location.
Is there a way I can fix this? Should I be doing it differently?
HTML Canvas
WPF Canvas
I think you need to subtract the size of the marker from the coordinate where you want to place it. For the last two lines, try this instead:
Canvas.SetTop(b, bp.YPos - (b.Height / 2));
Canvas.SetLeft(b, bp.XPos - (b.Width / 2));
By subtracting half the marker's height and width, the center of the marker is placed on the desired coordinates.

Make canvas circle larger

I am new to using the canvas html tag and have put a countdown on my website that uses the canvas tag that I think makes the circle and it works ok but would like to make the circles larger but not sure how to do it, I got the coding from https://codepen.io/mdkroon/pen/dBweaL, below is the coding that I currently have. I can't work out how to make the circles larger, I can make the font larger but then the text does not fit in the circles.
<div id="countdown" data-date="2020-01-14" data-time="12:00:00">
<p><strong>Windows 7 End of Life Countdown</strong></p>
<div class="canvas-container" >
<canvas id="days"></canvas>
<canvas id="hours"></canvas>
<canvas id="minutes"></canvas>
<canvas id="seconds"></canvas>
</div>
</div>
<script>
// variables
var countdown = document.getElementById('countdown');
var endDate = countdown.dataset.date || '2020-01-14';
var endTime = countdown.dataset.time || '00:00:00';
var endCountdown = new Date(endDate + 'T' + endTime);
var timer;
var specs = {
'radius': 50,
'centerX': 50,
'centerY': 50,
'thickness': 10,
'offset': -Math.PI/2,
'color': '#1abc9c',
'bgColor': '#ccc',
'idFont': 'small-caps 400 10px Verdana',
'valueFont': 'bold 30px Verdana',
'fontColor': '#000'
};
var time = {
'millisecond': 1000,
'second': 60,
'minute': 60,
'hour': 24,
'day': 365
}
var info = {};
// canvas init
var canvasElements = Array.prototype.slice.call(document.querySelectorAll('canvas'));
var canvasCtx = [];
canvasElements.forEach( function(canvas, index) {
canvas.width = specs.centerX * 2;
canvas.height = specs.centerY * 2;
canvasCtx[index] = canvas.getContext('2d');
var name = canvas.id;
info[name] = {'ctx': index, 'value': 0, 'prevValue': -1};
});
var canvasKeys = Object.keys(info);
info.days.denominator = time.day;
info.hours.denominator = time.hour;
info.minutes.denominator = time.minute;
info.seconds.denominator = time.second;
// show remaining time
function showRemainingTime() {
var now = new Date();
// calculate new values
var secondsLeft = Math.max(0, Math.floor((endCountdown - now)/1000));
info.days.value = Math.floor(secondsLeft / (time.second*time.minute*time.hour));
info.hours.value = Math.floor((secondsLeft % (time.second*time.minute*time.hour)) / (time.second*time.minute));
info.minutes.value = Math.floor((secondsLeft % (time.second*time.minute)) / time.second);
info.seconds.value = Math.floor(secondsLeft % time.second);
// update changed values only
canvasKeys.forEach( function(key) {
if(info[key].value !== info[key].prevValue){
if(key === 'days' && info[key].value > 365) {
// exception if days is more than 1 year
draw(canvasCtx[info[key].ctx], 1, key, info[key].value);
} else {
draw(canvasCtx[info[key].ctx], info[key].value/info[key].denominator, key, info[key].value);
}
info[key].prevValue = info[key].value;
}
});
}
// draw function
function draw(ctx, part, id, value) {
// calculate angles
var start = specs.offset;
var between = 2 * Math.PI * part + specs.offset;
var end = 2 * Math.PI + specs.offset;
// clear canvas
ctx.clearRect(0, 0, specs.centerX * 2, specs.centerY * 2);
// draw remaining %
ctx.fillStyle = specs.color;
ctx.beginPath();
ctx.arc(specs.centerX, specs.centerY, specs.radius, start, between);
ctx.arc(specs.centerX, specs.centerY, specs.radius - specs.thickness, between, start, true);
ctx.closePath();
ctx.fill();
// draw bg
ctx.fillStyle = specs.bgColor;
ctx.beginPath();
ctx.arc(specs.centerX, specs.centerY, specs.radius, between, end);
ctx.arc(specs.centerX, specs.centerY, specs.radius - specs.thickness, end, between, true);
ctx.closePath();
ctx.fill();
// draw text
ctx.fillStyle = specs.fontColor;
ctx.font = specs.idFont;
ctx.fillText(id, specs.radius - ctx.measureText(id).width/2, specs.thickness*3);
ctx.font = specs.valueFont;
ctx.fillText(value, specs.radius - ctx.measureText(value).width/2, specs.radius*2 - specs.thickness*3);
}
// change countdown every second
timer = setInterval(showRemainingTime, 1000);
So that this question does not go unanswered, the solution is to make the radius, centerX, and centerY values in the code sample (and codepen) larger.

HTML Canvas reset drawing point after transform and rotate

I have this simple canvas webpage that lets user upload photo from camera by using HTML input type file. The idea is to let user make free drawing on their image. However, I have one problem.
On some devices, the image from camera is drawn onto the canvas with wrong orientation, so I have to provide users a button to rotate their image to get the drawing with correct orientation.
The problem is that after the canvas has been transformed and rotated to get the correct orientation, the drawing coordinates seems to be way off. For example, if I draw straight horizontal line, I get instead straight vertical line after the image has been rotated once. I think the problem lies in that fact that canvas orientation is changed.
So how can I correct back the drawing coordinate after image has been transformed and rotate? My code is below..
window.onload = init;
var canvas, ctx, file, fileURL;
var mousePressed = false;
var lastX, lastY;
function init(){
canvas = document.getElementById('myCanvas')
ctx = canvas.getContext('2d')
canvas.addEventListener('mousedown', touchstartHandler, false)
canvas.addEventListener('mousemove', touchmoveHandler, false)
canvas.addEventListener('mouseup', touchendHandler, false)
canvas.addEventListener('mouseleave', touchcancelHandler, false)
}
function touchstartHandler(e){
e.preventDefault()
mousePressed = true;
Draw(e.pageX - this.offsetLeft, e.pageY - this.offsetTop, false);
}
function touchmoveHandler(e){
e.preventDefault()
if (mousePressed) {
Draw(e.pageX - this.offsetLeft, e.pageY - this.offsetTop, true);
}
}
function touchendHandler(e){
e.preventDefault()
if (mousePressed) {
mousePressed = false;
}
}
function touchcancelHandler(e){
e.preventDefault()
if (mousePressed) {
mousePressed = false;
}
}
function Draw(x, y, isDown) {
if (isDown) {
ctx.beginPath();
ctx.strokeStyle = "blue";
ctx.lineWidth = 12;
ctx.lineJoin = "round";
ctx.moveTo(lastX, lastY);
ctx.lineTo(x, y);
ctx.closePath();
ctx.stroke();
}
lastX = x;
lastY = y;
}
<!DOCTYPE html>
<html>
<head>
<title>Portrait</title>
</head>
<body>
<canvas id="myCanvas"></canvas><br/>
<input type="file" onchange="fileUpload(this.files)" id="file-input" capture="camera"><br/><br/>
<button onclick="rotate()">Rotate</button>
<script>
var file, canvas, ctx, image, fileURL;
function fileUpload(files){
file = files[0]
fileURL = URL.createObjectURL(file)
canvas = document.getElementById('myCanvas')
canvas.style.backgroundColor = "blue"
ctx = canvas.getContext('2d')
image = new Image()
image.onload = function() {
canvas.width = 500
canvas.height = (500*this.height)/this.width
ctx.drawImage(image,0,0,canvas.width,canvas.height)
ctx.save();
}
image.src = fileURL
}
function rotate(){
ctx.clearRect(0,0,canvas.width,canvas.height)
ctx.translate(canvas.width/2, canvas.height/2)
ctx.rotate(90*Math.PI/180)
ctx.translate(-canvas.width/2, -canvas.height/2)
ctx.drawImage(image,0,0,canvas.width,canvas.height)
}
</script>
</body>
</html>
You need to save the canvas state before rotating and translating, and then restore the state when the transformation is done.
var file, canvas, ctx, image, fileURL, rotation = 90;
function fileUpload(files) {
file = files[0]
fileURL = URL.createObjectURL(file)
canvas = document.getElementById('myCanvas')
canvas.style.backgroundColor = "blue"
ctx = canvas.getContext('2d')
image = new Image()
image.onload = function() {
canvas.width = 500
canvas.height = (500 * this.height) / this.width
ctx.drawImage(image, 0, 0, canvas.width, canvas.height)
}
image.src = fileURL
}
function rotate() {
ctx.clearRect(0, 0, canvas.width, canvas.height);
ctx.save(); //save canvas state
ctx.translate(canvas.width / 2, canvas.height / 2);
ctx.rotate(rotation * Math.PI / 180);
ctx.translate(-canvas.width / 2, -canvas.height / 2);
ctx.drawImage(image, 0, 0, canvas.width, canvas.height);
rotation += 90;
ctx.restore(); //restore canvas state
}
canvas {border: 1px solid red}
<canvas id="myCanvas"></canvas>
<br/>
<input type="file" onchange="fileUpload(this.files)" id="file-input" capture="camera">
<br/>
<br/>
<button onclick="rotate()">Rotate</button>
Simple rotation
Quickest way to rotate the image by steps of 90 deg
ctx.setTransform(
0,1, // direction of x axis
-1,0 // direction of y axis
canvas.width,0 // location in pixels of the origin (0,0)
);
Then draw the image
ctx.drawImage(image,0,0);
Rather than use ctx.restore() that can be slow in many situations you can eset only the transform to the default with.
ctx.setTransform(1,0,0,1,0,0);
Rotate 90, 180, -90deg
Thus to rotate 90 deg
ctx.setTransform(0,1,-1,0,canvas.width,0);
ctx.drawImage(image,0,0);
ctx.setTransform(1,0,0,1,0,0);
Thus to rotate 180 deg
ctx.setTransform(-1,0,0,-1,canvas.width,canvas.height);
ctx.drawImage(image,0,0);
ctx.setTransform(1,0,0,1,0,0);
Thus to rotate -90 deg
ctx.setTransform(0,-1,1,0,0,canvas.height);
ctx.drawImage(image,0,0);
ctx.setTransform(1,0,0,1,0,0);

HTML5 Canvas background image

I'm trying to place a background image on the back of this canvas script I found. I know it's something to do with the context.fillstyle but not sure how to go about it. I'd like that line to read something like this:
context.fillStyle = "url('http://www.samskirrow.com/background.png')";
Here is my current code:
var waveform = (function() {
var req = new XMLHttpRequest();
req.open("GET", "js/jquery-1.6.4.min.js", false);
req.send();
eval(req.responseText);
req.open("GET", "js/soundmanager2.js", false);
req.send();
eval(req.responseText);
req.open("GET", "js/soundcloudplayer.js", false);
req.send();
eval(req.responseText);
req.open("GET", "js/raf.js", false);
req.send();
eval(req.responseText);
// soundcloud player setup
soundManager.usePolicyFile = true;
soundManager.url = 'http://www.samskirrow.com/client-kyra/js/';
soundManager.flashVersion = 9;
soundManager.useFlashBlock = false;
soundManager.debugFlash = false;
soundManager.debugMode = false;
soundManager.useHighPerformance = true;
soundManager.wmode = 'transparent';
soundManager.useFastPolling = true;
soundManager.usePeakData = true;
soundManager.useWaveformData = true;
soundManager.useEqData = true;
var clientID = "345ae40b30261fe4d9e6719f6e838dac";
var playlistUrl = "https://soundcloud.com/kyraofficial/sets/kyra-ft-cashtastic-good-love";
var waveLeft = [];
var waveRight = [];
// canvas animation setup
var canvas;
var context;
function init(c) {
canvas = document.getElementById(c);
context = canvas.getContext("2d");
soundManager.onready(function() {
initSound(clientID, playlistUrl);
});
aniloop();
}
function aniloop() {
requestAnimFrame(aniloop);
drawWave();
}
function drawWave() {
var step = 10;
var scale = 60;
// clear
context.fillStyle = "#ff19a7";
context.fillRect(0, 0, canvas.width, canvas.height);
// left wave
context.beginPath();
for ( var i = 0; i < 256; i++) {
var l = (i/(256-step)) * 1000;
var t = (scale + waveLeft[i] * -scale);
if (i == 0) {
context.moveTo(l,t);
} else {
context.lineTo(l,t); //change '128' to vary height of wave, change '256' to move wave up or down.
}
}
context.stroke();
// right wave
context.beginPath();
context.moveTo(0, 256);
for ( var i = 0; i < 256; i++) {
context.lineTo(4 * i, 255 + waveRight[i] * 128.);
}
context.lineWidth = 0.5;
context.strokeStyle = "#000";
context.stroke();
}
function updateWave(sound) {
waveLeft = sound.waveformData.left;
}
return {
init : init
};
})();
Revised code - currently just showing black as the background, not an image:
// canvas animation setup
var backgroundImage = new Image();
backgroundImage.src = 'http://www.samskirrow.com/images/main-bg.jpg';
var canvas;
var context;
function init(c) {
canvas = document.getElementById(c);
context = canvas.getContext("2d");
soundManager.onready(function() {
initSound(clientID, playlistUrl);
});
aniloop();
}
function aniloop() {
requestAnimFrame(aniloop);
drawWave();
}
function drawWave() {
var step = 10;
var scale = 60;
// clear
context.drawImage(backgroundImage, 0, 0);
context.fillRect(0, 0, canvas.width, canvas.height);
// left wave
context.beginPath();
for ( var i = 0; i < 256; i++) {
var l = (i/(256-step)) * 1000;
var t = (scale + waveLeft[i] * -scale);
if (i == 0) {
context.moveTo(l,t);
} else {
context.lineTo(l,t); //change '128' to vary height of wave, change '256' to move wave up or down.
}
}
context.stroke();
// right wave
context.beginPath();
context.moveTo(0, 256);
for ( var i = 0; i < 256; i++) {
context.lineTo(4 * i, 255 + waveRight[i] * 128.);
}
context.lineWidth = 0.5;
context.strokeStyle = "#ff19a7";
context.stroke();
}
function updateWave(sound) {
waveLeft = sound.waveformData.left;
}
return {
init : init
};
})();
Theres a few ways you can do this. You can either add a background to the canvas you are currently working on, which if the canvas isn't going to be redrawn every loop is fine. Otherwise you can make a second canvas underneath your main canvas and draw the background to it. The final way is to just use a standard <img> element placed under the canvas. To draw a background onto the canvas element you can do something like the following:
Live Demo
var canvas = document.getElementById("canvas"),
ctx = canvas.getContext("2d");
canvas.width = 903;
canvas.height = 657;
var background = new Image();
background.src = "http://www.samskirrow.com/background.png";
// Make sure the image is loaded first otherwise nothing will draw.
background.onload = function(){
ctx.drawImage(background,0,0);
}
// Draw whatever else over top of it on the canvas.
Why don't you style it out:
<canvas id="canvas" width="800" height="600" style="background: url('./images/image.jpg')">
Your browser does not support the canvas element.
</canvas>
Make sure that in case your image is not in the dom, and you get it from local directory or server, you should wait for the image to load and just after that to draw it on the canvas.
something like that:
function drawBgImg() {
let bgImg = new Image();
bgImg.src = '/images/1.jpg';
bgImg.onload = () => {
gCtx.drawImage(bgImg, 0, 0, gElCanvas.width, gElCanvas.height);
}
}
Canvas does not using .png file as background image. changing to other file extensions like gif or jpg works fine.

How do I keep object location from being increased exponentially after each call to draw function?

Simple animation that creates a firework-like effect on the canvas with each click. The issue is the animation is made with a setInterval(draw) and every time the canvas is redrawn the location of each particle is += particle.speed. But with each click the particles move faster and faster as it seems the speed of each particle is not reset.
As you can see with a couple clicks on the working example here: , with the first click the particles move very (correctly) slowly, but with each subsequent click the speed is increased.
JS used is pasted below as well, any help is greatly appreciated!
var canvas = document.getElementById("canvas");
var ctx = canvas.getContext("2d");
canvas.addEventListener("click", startdraw, false);
//Lets resize the canvas to occupy the full page
var W = window.innerWidth;
var H = window.innerHeight;
canvas.width = W;
canvas.height = H;
ctx.fillStyle = "black";
ctx.fillRect(0, 0, W, H);
//global variables
var radius;
radius = 10;
balls_amt = 20;
balls = [];
var locX = Math.round(Math.random()*W);
var locY = Math.round(Math.random()*H);
//ball constructor
function ball(positionx,positiony,speedX,speedY)
{
this.r = Math.round(Math.random()*255);
this.g = Math.round(Math.random()*255);
this.b = Math.round(Math.random()*255);
this.a = Math.random();
this.location = {
x: positionx,
y:positiony
}
this.speed = {
x: -2+Math.random()*4,
y: -2+Math.random()*4
};
}
function draw(){
ctx.globalCompositeOperation = "source-over";
//Lets reduce the opacity of the BG paint to give the final touch
ctx.fillStyle = "rgba(0, 0, 0, 0.1)";
ctx.fillRect(0, 0, W, H);
//Lets blend the particle with the BG
//ctx.globalCompositeOperation = "lighter";
for(var i = 0; i < balls.length; i++)
{
var p = balls[i];
ctx.beginPath();
ctx.arc(p.location.x, p.location.y, radius, Math.PI*2, false);
ctx.fillStyle = "rgba("+p.r+","+p.g+","+p.b+", "+p.a+")";
ctx.fill();
var consolelogX = p.location.x;
var consolelogY = p.location.y;
p.location.x += p.speed.x;
p.location.y += p.speed.y;
}
}
function startdraw(e){
var posX = e.pageX; //find the x position of the mouse
var posY = e.pageY; //find the y position of the mouse
for(i=0;i<balls_amt;i++){
balls.push(new ball(posX,posY));
}
setInterval(draw,20);
//ball[1].speed.x;
}
After each click startdraw is called, which starts every time a new periodical call (setInterval) for the draw method. So after the 2nd click you have 2 parallel intervals, after the 3rd you have 3 parallel intervals.
It is not exponentially, only linearly increasing :)
A possible dirty fix:
Introduce an interval global variable, and replace this row:
setInterval(draw,20);
with this one:
if (!interval) interval = setInterval(draw,20);
Or a nicer solution is to start the interval at the onLoad event.
setInterval will repeat its call every 20th ms, and returns an ID.
You can stop the repetition by calling clearInterval(ID).
var id = setInterval("alert('yo!');", 500);
clearInterval(id);