Tag: code

I’m really enjoying giving a control panel of sorts to the end user and letting them control the physics rules of their canvas. Let’s add more motion to it by applying a jitter to the velocity of each dot. This is similar to earlier, when we first started animating by applying a random number to the coordinates, but now we’ll apply a (smaller) random number to the velocity. This will be much smoother and will give a sense of real life to the dots. Straight lines and trajectories is always theoretical and hypothetical, but to make things look more real, sometimes we have to break the clean, straight lines. This will be another checkbox to control the float. I’m really enjoying the fact that the more properties we add to our controls we get exponentially more possible configurations. Perhaps we should even give a slider to control the strength of gravity…
interactive physics animations via javascript & canvas | 17.

[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 = 0;
var friction = .98;
var bounce = -.96;
var wrap = false;
var float = true;

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; }); $("#canvas").mousemove(function (event) { if(drag) { dots[drag_i].old_x = dots[drag_i].x; dots[drag_i].old_y = dots[drag_i].y; dots[drag_i].x = event.pageX - this.offsetLeft - clickX; dots[drag_i].y = event.pageY - this.offsetTop - clickY; dots[drag_i].vx = dots[drag_i].x - dots[drag_i].old_x; dots[drag_i].vy = dots[drag_i].y - dots[drag_i].old_y; draw(); } }); function update(){ for (var i=0; i < dots.length; i++){ if (drag_i != i){ var this_dot = dots[i]; if (float){ this_dot.vx += Math.random() - .5; this_dot.vy += Math.random() - .5; } this_dot.vx *= friction; this_dot.vy = this_dot.vy * friction + gravity; this_dot.x += this_dot.vx; this_dot.y += this_dot.vy; if (wrap){ if (this_dot.x > canvas.width + this_dot.radius){
this_dot.x -= canvas.width + this_dot.radius*2;
}
else if(this_dot.x < 0 - this_dot.radius){ this_dot.x += canvas.width + this_dot.radius*2; } if (this_dot.y > canvas.height + this_dot.radius){
this_dot.y -= canvas.height + this_dot.radius*2;
}
else if(this_dot.y < 0 - this_dot.radius){ this_dot.y += canvas.height + this_dot.radius*2; } } else if (!wrap) { if (this_dot.x > canvas.width – this_dot.radius){
this_dot.x = canvas.width – this_dot.radius;
this_dot.vx = this_dot.vx * bounce;
}
else if(this_dot.x < 0 + this_dot.radius){ this_dot.x = this_dot.radius; this_dot.vx = this_dot.vx * bounce; } if (this_dot.y > canvas.height – this_dot.radius){
this_dot.y = canvas.height – this_dot.radius;
this_dot.vy = this_dot.vy * bounce;
}
else if(this_dot.y < 0 + this_dot.radius){ this_dot.y = this_dot.radius; this_dot.vy = this_dot.vy * bounce; } } } } } function draw() { context.clearRect(0, 0, canvas.width, canvas.height); for (var i=0; i < dots.length; i++){ context.beginPath(); context.arc(dots[i].x, dots[i].y, dots[i].radius, 0, Math.PI * 2, false); context.fill(); context.closePath(); } } setInterval(function() { update(); draw(); }, 1000/fps);$("#gravity").click(function(){ if($("#gravity").is(':checked')){ gravity = 2; } else{ gravity = 0; } }); $("#wrap").click(function(){ if($("#wrap").is(':checked')){ wrap = true; } else{ wrap = false; } }); $("#float").click(function(){ if($("#float").is(':checked')){ float = true; } else{ float = false; } }); }); [/cc]Follow the whole Interactive Physics Animations via Javascript & Canvas series.

I always want to give the end user (at least some) control of how they view and interact with data. Earlier we gave users control over gravity. Here let’s give them control over the canvas edges. Rather than having our dots bounce on the edges of the canvas, lets have them wrap across to the other side. Like in the asteroids game the ship can fly to the edge of the screen and see space wrap them back to the other side. We’ll set this up as a control exposed to the user much like gravity. Let’s call it wrap and use a boolean value to store the setting. We’ll need to add another block of conditionals for this case where we have the set already with the bouncing. I took some care with the values so that the dots leave the canvas before they make the hyper-jump to the other side. Otherwise you’d see the magic. interactive physics animations via javascript & canvas | 16.

[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 = 0;
var friction = .98;
var bounce = -.96;
var wrap = true;

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; }); $("#canvas").mousemove(function (event) { if(drag) { dots[drag_i].old_x = dots[drag_i].x; dots[drag_i].old_y = dots[drag_i].y; dots[drag_i].x = event.pageX - this.offsetLeft - clickX; dots[drag_i].y = event.pageY - this.offsetTop - clickY; dots[drag_i].vx = dots[drag_i].x - dots[drag_i].old_x; dots[drag_i].vy = dots[drag_i].y - dots[drag_i].old_y; draw(); } }); function update(){ for (var i=0; i < dots.length; i++){ if (drag_i != i){ var this_dot = dots[i]; this_dot.vx *= friction; this_dot.vy = this_dot.vy * friction + gravity; this_dot.x += this_dot.vx; this_dot.y += this_dot.vy; if (wrap){ if (this_dot.x > canvas.width + this_dot.radius){
this_dot.x -= canvas.width + this_dot.radius*2;
}
else if(this_dot.x < 0 - this_dot.radius){ this_dot.x += canvas.width + this_dot.radius*2; } if (this_dot.y > canvas.height + this_dot.radius){
this_dot.y -= canvas.height + this_dot.radius*2;
}
else if(this_dot.y < 0 - this_dot.radius){ this_dot.y += canvas.height + this_dot.radius*2; } } else if (!wrap) { if (this_dot.x > canvas.width – this_dot.radius){
this_dot.x = canvas.width – this_dot.radius;
this_dot.vx = this_dot.vx * bounce;
}
else if(this_dot.x < 0 + this_dot.radius){ this_dot.x = this_dot.radius; this_dot.vx = this_dot.vx * bounce; } if (this_dot.y > canvas.height – this_dot.radius){
this_dot.y = canvas.height – this_dot.radius;
this_dot.vy = this_dot.vy * bounce;
}
else if(this_dot.y < 0 + this_dot.radius){ this_dot.y = this_dot.radius; this_dot.vy = this_dot.vy * bounce; } } } } } function draw() { context.clearRect(0, 0, canvas.width, canvas.height); for (var i=0; i < dots.length; i++){ context.beginPath(); context.arc(dots[i].x, dots[i].y, dots[i].radius, 0, Math.PI * 2, false); context.fill(); context.closePath(); } } setInterval(function() { update(); draw(); }, 1000/fps);$("#gravity").click(function(){ if($("#gravity").is(':checked')){ gravity = 2; } else{ gravity = 0; } }); $("#wrap").click(function(){ if($("#wrap").is(':checked')){ wrap = true; } else{ wrap = false; } }); }); [/cc]Follow the whole Interactive Physics Animations via Javascript & Canvas series.

Earlier we worked on making all the dots draggable, but what’s better than simply dragging dots? Let’s set up a way to throw the dots! Now as we drag it we record the positions and use that to calculate a new velocity. Then when a dot is dropped, it will have a trajectory to follow that matches the path and speed it was dragged. This iteration only looks at the current frame and the previous frame, but a better solution may be to average the previous few positions to get a better feel. I’ve noticed that (with a mouse especially) people tend to stop dragging just before they mouseup, so this kills any velocity the dot receives during the drag. Enjoy throwing the dots around the canvas! interactive physics animations via javascript & canvas | 15.

[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; }); $("#canvas").mousemove(function (event) { if(drag) { dots[drag_i].old_x = dots[drag_i].x; dots[drag_i].old_y = dots[drag_i].y; dots[drag_i].x = event.pageX - this.offsetLeft - clickX; dots[drag_i].y = event.pageY - this.offsetTop - clickY; dots[drag_i].vx = dots[drag_i].x - dots[drag_i].old_x; dots[drag_i].vy = dots[drag_i].y - dots[drag_i].old_y; draw(); } }); function update(){ for (var i=0; i < dots.length; i++){ if (drag_i != i){ var this_dot = dots[i]; this_dot.vx *= friction; this_dot.vy = this_dot.vy * friction + gravity; this_dot.x += this_dot.vx; this_dot.y += this_dot.vy; if (this_dot.x > canvas.width – this_dot.radius){
this_dot.x = canvas.width – this_dot.radius;
this_dot.vx = this_dot.vx * bounce;
}
else if(this_dot.x < 0 + this_dot.radius){ this_dot.x = this_dot.radius; this_dot.vx = this_dot.vx * bounce; } if (this_dot.y > canvas.height – this_dot.radius){
this_dot.y = canvas.height – this_dot.radius;
this_dot.vy = this_dot.vy * bounce;
}
else if(this_dot.y < 0 + this_dot.radius){ this_dot.y = this_dot.radius; this_dot.vy = this_dot.vy * bounce; } } } } function draw() { context.clearRect(0, 0, canvas.width, canvas.height); for (var i=0; i < dots.length; i++){ context.beginPath(); context.arc(dots[i].x, dots[i].y, dots[i].radius, 0, Math.PI * 2, false); context.fill(); context.closePath(); } } setInterval(function() { update(); draw(); }, 1000/fps);$("#gravity").click(function(){ if($("#gravity").is(':checked')){ gravity = 2; } else{ gravity = 0; } }); }); [/cc]Follow the whole Interactive Physics Animations via Javascript & Canvas series.