Here is an update to allow the end user to create more dots. A good way to do that is to just let users click on the canvas, and if they click a dot, drag it, if they don’t click a dot, create a new dot at the point of click. I moved the dot creation into it’s own function and we can use that as our constructor for every dot. It has settings we can send in, but the defaults are set to pick random values. This could also be used to create a particle emitter of sorts, but for now it’s just creating a dot on clicking the blank canvas. interactive physics animations via javascript & canvas | 14.
[cc lang=”javascript”]
$(function () {
var canvas, context, width, height, x, y, radius = 25, clickX, clickY, drag = false;
var total_dots = 10;
var fps = 24;
canvas = $(“#canvas”)[0];
context = canvas.getContext(“2d”);
var dots = new Array();
var drag_i = -1;
var gravity = 2;
var friction = .98;
var bounce = -.96;
var this_dot = {};
for (var i=0; i < total_dots; i++){
createDot();
}
function createDot(x, y, r, vx, vy){
var this_dot = {
x: typeof(x) != 'undefined' ? x : Math.random()*canvas.width,
y: typeof(y) != 'undefined' ? y : Math.random()*canvas.height,
radius: typeof(r) != 'undefined' ? r : Math.random()*20+10,
vx: typeof(vx) != 'undefined' ? vx : Math.random()*30-10,
vy: typeof(vy) != 'undefined' ? vy : Math.random()*30-10
};
dots.push(this_dot);
}
draw();
$("#canvas").mousedown(function (event) {
var dx, dy, dist;
for (var i=0; i < dots.length; i++){
dx = event.pageX - this.offsetLeft - dots[i].x;
dy = event.pageY - this.offsetTop - dots[i].y;
dist = Math.sqrt(dx * dx + dy * dy);
if(dist < radius) {
drag = true;
drag_i = i
clickX = dx;
clickY = dy;
continue;
}
}
//none clicked
if (!drag) {
createDot(event.pageX - this.offsetLeft, event.pageY - this.offsetTop);
}
});
$("#canvas").mouseup(function (event) {
drag = false;
drag_i = -1;
});
$("#canvas").mousemove(function (event) {
if(drag) {
dots[drag_i].x = event.pageX - this.offsetLeft - clickX;
dots[drag_i].y = event.pageY - this.offsetTop - clickY;
draw();
}
});
function update(){
for (var i=0; i < dots.length; i++){
if (drag_i != i){
var this_dot = dots[i];
this_dot.vx *= friction;
this_dot.vy = this_dot.vy * friction + gravity;
this_dot.x += this_dot.vx;
this_dot.y += this_dot.vy;
if (this_dot.x > canvas.width – this_dot.radius){
this_dot.x = canvas.width – this_dot.radius;
this_dot.vx = this_dot.vx * bounce;
}
else if(this_dot.x < 0 + this_dot.radius){
this_dot.x = this_dot.radius;
this_dot.vx = this_dot.vx * bounce;
}
if (this_dot.y > canvas.height – this_dot.radius){
this_dot.y = canvas.height – this_dot.radius;
this_dot.vy = this_dot.vy * bounce;
}
else if(this_dot.y < 0 + this_dot.radius){
this_dot.y = this_dot.radius;
this_dot.vy = this_dot.vy * bounce;
}
}
}
}
function draw() {
context.clearRect(0, 0, canvas.width, canvas.height);
for (var i=0; i < dots.length; i++){
context.beginPath();
context.arc(dots[i].x, dots[i].y, dots[i].radius, 0, Math.PI * 2, false);
context.fill();
context.closePath();
}
}
setInterval(function() {
update();
draw();
}, 1000/fps);$("#gravity").click(function(){
if($("#gravity").is(':checked')){
gravity = 2;
}
else{
gravity = 0;
}
});
});
[/cc]Follow the whole Interactive Physics Animations via Javascript & Canvas series.