Related
Good day,
I am generating some circles with colors, sizes and positions. All of this things randomly.
But, my problem is that I do not want them to collide, so that no circle is inside another, not even a little bit.
The logic explained in detail within the code, I would like to know why the failure and why the infinite loop.
The important functions are:
checkSeparation and setPositions
window.addEventListener("load", draw);
function draw() {
var canvas = document.getElementById("balls"), // Get canvas
ctx = canvas.getContext("2d"); // Context
canvas.width = document.body.clientWidth; // Set canvas width
canvas.height = document.documentElement.scrollHeight; // Height
var cW = canvas.width, cH = canvas.height; // Save in vars
ctx.fillStyle = "#fff022"; // Paint background
ctx.fillRect(0, 0, cW, cH); // Coordinates to paint
var arrayOfBalls = createBalls(); // create all balls
setPositions(arrayOfBalls, cW, cH);
arrayOfBalls.forEach(ball => { // iterate balls to draw
ctx.beginPath(); // start the paint
ctx.fillStyle = ball.color;
ctx.arc(ball.x, ball.y, ball.radius, 0, (Math.PI/180) * 360, false); // draw the circle
ctx.fill(); // fill
ctx.closePath(); // end the paint
});
}
function Ball() {
this.x = 0; // x position of Ball
this.y = 0; // y position of Ball
this.radius = Math.floor(Math.random() * ( 30 - 10 + 1) + 10);
this.color = "";
}
Ball.prototype.setColor = function(){
for(var j = 0, hex = "0123456789ABCDEF", max = hex.length,
random, str = ""; j <= 6; j++, random = Math.floor(Math.random() * max), str += hex[random])
this.color = "#" + str;
};
function random(val, min) {
return Math.floor(Math.random() * val + min); // Random number
}
function checkSeparation(value, radius, toCompare) {
var min = value - radius, // Min border of circle
max = value + radius; // Max border of circle
// Why ? e.g => x position of circle + this radius it will be its right edge
for(; min <= max; min++) {
if(toCompare.includes(min)) return false;
/*
Since all the positions previously obtained, I add them to the array, in order to have a reference when verifying the other positions and that they do NOT collide.
Here I check if they collide.
In the range of:
[pos x - its radius, pos x + its radius]
*/
}
return true; // If they never collided, it returns true
}
function createBalls() {
var maxBalls = 50, // number of balls
balls = []; // array of balls
for(var j = 0; j < maxBalls; j++) { // create 50 balls
var newBall = new Ball(); // create ball
newBall.setColor(); // set the ball color
balls.push(newBall); //push the ball to the array of balls
}
return balls; // return all balls to draw later
}
function setPositions(balls, canvasW, canvasH) {
var savedPosX = [], // to save x pos of balls
savedPosY = []; // to save y pos of balls
for(var start = 0, max = balls.length; start < max; start++) {
var current = balls[start], // current ball
randomX = random(canvasW, current.radius), // get random value for x pos
randomY = random(canvasH, current.radius); // get random value for y pos
if(checkSeparation(randomX, current.radius, savedPosX)) {
current.x = randomX; // If it position, along with your radio does not touch another circle, I add the position
} else {
// start--; continue;
console.log("X: The above code causes an infinite loop");
}
if(checkSeparation(randomY, current.radius, savedPosY)) {
current.y = randomY;
} else {
// start--; continue;
console.log("Y: The above code causes an infinite loop");
}
}
}
body,html {
margin: 0; border: 0; padding: 0; overflow: hidden;
}
<canvas id="balls"></canvas>
In your code, you test possible collisions by means of arrays of already used x and y positions, but you never add new positions to these arrays. You also check the x and y coordinates separately, which means you are really testing a collision of a bounding box.
Two circles collide when the distance between their centres is smaller than the sum of their radii, so you could use:
function collides(balls, n, x, y, r) {
for (let i = 0; i < n; i++) {
let ball = balls[i];
let dx = ball.x - x;
let dy = ball.y - y;
let dd = dx*dx + dy*dy;
let rr = r + ball.radius;
if (dd < rr * rr) return true;
}
return false;
}
function setPositions(balls, canvasW, canvasH) {
for (let i = 0, max = balls.length; i < max; i++) {
let ball = balls[i],
r = ball.radius,
maxTries = 20;
ball.x = -canvasW;
ball.y = -canvasH;
for (let tries = 0; tries = maxTries; tries++) {
let x = random(canvasW - 2*r, r),
y = random(canvasH - 2*r, r);
if (!collides(balls, i, x, y, r)) {
ball.x = x;
ball.y = y;
break;
}
}
}
}
This is reasonably fast for 50 balls, but will be slow if you have more balls. In that case, some spatial data structures can speed up the collision search.
You must also guard against the case that no good place can be found. The code above gives up after 20 tries and moves the ball outside the visible canvas. You can improve the chances of placing balls by sorting the balls by radius and plaing the large balls first.
Finally, you add one hex digit too many to your random colour. (That for loop, where everything happens in the loop control is horrible, by the way.)
So I am trying to implement a concept of shooting star over an already drawn canvas of slowly moving stars. But I haven't found a way to do so. I tried implementing an array to make it look so but the trail isn't as efficient.
This code is as follows:
var canvas = document.querySelector('canvas');
var c = canvas.getContext('2d');
canvas.width = window.innerWidth;
canvas.height = window.innerHeight;
var mouse = {
x : innerWidth/2,
y : innerHeight/2
};
var colors = [
'#3399CC',
'#67B8DE',
'#91C9E8',
'#B4DCED',
'#E8F8FF'
];
addEventListener('resize', function () {
canvas.width = innerWidth;
canvas.height = innerHeight;
init();
});
var isClicked = false;
addEventListener('click', function () {
mouse.x = event.clientX;
mouse.y = event.clientY;
isClicked = true;
});
function randomIntFromRange (min, max) {
return Math.floor(Math.random() * (max - min + 1) + min);
}
function randomColor (colors) {
return colors[Math.floor(Math.random() * colors.length)];
}
function Stars (x, y, radius, dy, color) {
this.x = x;
this.y = y;
this.radius = radius;
this.dy = dy;
this.color = color;
this.draw = function () {
c.beginPath();
c.arc(this.x, this.y, this.radius, 0, 2 * Math.PI, false);
c.shadowColor = this.color;
c.shadowBlur = 15;
c.shadowOffsetX = 0;
c.shadowOffsetY = 0;
c.fillStyle = this.color;
c.fill();
c.closePath();
}
this.update = function () {
if (this.y < -10) {
this.y = canvas.height + 10;
this.x = randomIntFromRange(this.radius, canvas.width);
}
this.y -= this.dy;
this.draw();
}
}
function ShootingStar (x, y, radius) {
this.x = x;
this.y = y;
this.radius = radius;
this.draw = function () {
c.beginPath();
c.arc(this.x, this.y, this.radius, 0, 2 * Math.PI, false);
c.shadowColor = "red";
c.shadowBlur = 15;
c.shadowOffsetX = 0;
c.shadowOffsetY = 0;
c.fillStyle = "red";
c.fill();
c.closePath();
}
this.update = function () {
this.x += 10;
this.y += 10;
this.draw();
}
}
let stars = [];
let shooting_star = [];
function init () {
stars = [];
for (var i = 0; i < 300; i++) {
var stars_radius = randomIntFromRange(2, 3);
var stars_x = randomIntFromRange(stars_radius, canvas.width);
var stars_y = randomIntFromRange(stars_radius, canvas.height);
var stars_dy = Math.random() / 6;
var color = randomColor(colors);
stars.push(new Stars(stars_x, stars_y, stars_radius, stars_dy, color));
}
}
function Explode () {
shooting_star = [];
var shooting_star_radius = 3;
var shooting_star_x = mouse.x;
var shooting_star_y = mouse.y;
for (var i = 0; i < 50; i++) {
shooting_star.push(new ShootingStar(shooting_star_x, shooting_star_y, shooting_star_radius));
if (shooting_star_radius > 0.2) {
shooting_star_radius -= .2;
}
var initiator = randomIntFromRange(-1, 1);
console.log(initiator);
shooting_star_x -= 3;
shooting_star_y -= 3;
}
}
function animate () {
requestAnimationFrame(animate);
c.clearRect(0, 0, canvas.width, canvas.height);
for (var i = 0; i < stars.length; i++)
stars[i].update();
for (var i = 0; i < shooting_star.length; i++)
shooting_star[i].update();
if (isClicked == true) {
Explode();
isClicked = false;
}
}
init();
animate();
Here is the jsfiddle to it
https://jsfiddle.net/qjug4qdz/
I basically want the shooting star to come from a random location to the point where my mouse is clicked, but the trail is difficult to work with using an array.
Basic particles
For the particular effect you are looking for you can use a basic particle system.
As the shooting star moves you will drop a particle that starts with the star velocity and then slows and fades out.
The particle
You first start with the particle. I like to use Object.assign when creating objects but you can use any method you like, class, new, factory...
// This defines a particle and is copied to create new particles
const starDust = {
x : 0, // the current position
y : 0,
dx : 0, // delta x,y (velocity)
dy : 0,
drag : 0, // the rate that the particle slows down.
life : 0, // count down till particle is removed
age : 0, // the starting value of life
draw(){ // function to update and draw the particle
this.x += this.dx; // move it
this.y += this.dy;
this.dx *= this.drag; // slow it down
this.dy *= this.drag;
const unitLife = (this.life / this.age); // get the life left as a value
// from 0 to 1 where 0 is end
ctx.globalAlpha = unitLife; // set the alpha
ctx.beginPath();
ctx.arc(this.x,this.y,4,0,Math.PI); // draw the particle
this.life -= 1; // count down
return this.life > 0; // return true if still alive
}
Be memory aware.
A common mistake when creating particle systems is that people forget that creating and destroying objects will add a lot of work to javascripts memory management. The worst of which is GC (Garbage Collection). GC is a major source of lag and if you are wasteful with memory it will impact the quality of the animation. For simple particles it may not be noticeable, but you may want hundreds of complex particles spawning each frame. This is when GC realy hurts the animation.
Most Game engines reduce the GC impact by reusing objects rather than dereferencing and recreating. A common method is an object pool, where a second array holds objects that are no longer used. When a new object is needed then the pool is first checked, if there is an unused object, it is used, else a new object is created.
This way you never delete any particles, greatly reducing the GC workload, and preventing your animation from dropping frames (if you use a lot of particles)
Particle needs initializer
But you need to provide a way to re-initialize the object. Thus add the function init to the particle that will set it up to be used again
init(x,y,vx,vy){ // where x,y and velocity vx,vy of shooting star
this.x = x;
this.y = y;
this.dx = vx;
this.dy = vy;
// give a random age
this.age = (Math.random() * 100 + 60) | 0; // in frames and | 0 floors the value
this.life = this.age; // and set the life countdown
this.drag = Math.random() * 0.01 + 0.99; // the drag that slows the particle down
}
} // end of starDust object.
The arrays
To manage all the particles we create object that has arrays and methods for adding, creating and rendering the particles. In this case I will call it dust
const dust = {
particles : [], // array of active particles
pool : [], // array of unused particels
createParticle(particleDesc){ // creates a new particle from particleDesc
return Object.assign({},particleDesc);
},
add(x,y,vx,vy){ // where x,y and velocity vx,vy
var dust;
if(this.pool.length){ // are there any particles in the pool
dust = this.pool.pop(); // get one
}else{ // else there are no spare particles so create a new one
dust = this.createParticle(starDust);
}
dust.init(x,y,vx,vy); // init the particle
this.items.push(dust); // put it in the active particle array
return dust; // return it (sometimes you want to do something with it)
},
draw(){ // updates and draws all active particles
var i = 0;
while(i < this.items.length){ // iterate each particle in items
if(this.items[i].draw() === false){ // is it dead??
this.pool.push(this.items.splice(i,1)[0]); // if dead put in the pool for later
}else{ i ++ } // if not dead get index of next particle
}
}
}//end of dust object
Using the particle system
The simplest way to create a particle is to use a random number and set the chance of a particle being created every frame.
In your main loop
// assuming that the falling star is called star and has an x,y and dx,dy (delta)
if(star) { // only if there is a start to spawn from
// add a particle once every 10 frame (on average
if(Math.random() < 0.1) {
dust.add(star.x, star.y, star.dx, star.dy); // add some dust at the shooting starts position and speed
}
}
dust.draw(); // draw all particles
And that is it.
I'm really struggling with a couple problems in the HTML5 canvas.
I've posted the project to GitHub pages (https://swedy13.github.io/) and added an image (the circles are in motion) so you can see the issue. Basically, if you scroll down you'll find several green circles bouncing around on the page. I'd like to replace those with my client logos.
I'm calling requestAnimation from three files based on different actions, all of which can be found in https://github.com/swedy13/swedy13.github.io/tree/master/assets/js
Filenames:
- filters.js (calls requestAnimation when you use the filters)
- main.js (on load and resize)
- portfolio.js (this is where the canvas code is)
Update: I've added the "portfolio.js" code below so the answer can be self-contained.
function runAnimation(width, height, type){
var canvas = document.getElementsByTagName('canvas')[0];
var c = canvas.getContext('2d');
// ---- DIMENSIONS ---- //
// Container
var x = width;
var y = height - 65;
canvas.width = x;
canvas.height = y;
var container = {x: 0 ,y: 0 ,width: x, height: y};
// Portrait Variables
var cPos = 200;
var cMargin = 70;
var cSpeed = 3;
var r = x*.075;
if (y > x && x >= 500) {
cPos = x * (x / y) - 150;
cMargin = 150;
}
// Landscape Variables
if (x > y) {
cPos = y * (y / x) - 50;
cMargin = 150;
cSpeed = 3;
r = x*.05;
}
// ---- CIRCLES ---- //
// Circles
var circles = [];
var img = new Image();
// Gets active post ids and count
var activeName = [];
var activeLogo = [];
var activePosts = $('.active').map(function() {
activeName.push($(this).text().replace(/\s+/g, '-').toLowerCase());
// Returns the image source
/*activeLogo.push($(this).find('img').prop('src'));*/
// Returns an image node
var elem = document.getElementsByClassName($(this).text().replace(/\s+/g, '-').toLowerCase())
activeLogo.push(elem[0].childNodes[0]);
});
// Populates circle data
for (var i = 0; i < $('.active').length; i++) {
circles.push({
id:activeName[i],
r:r,
color: 100,
/*image: activeLogo[i],*/
x:Math.random() * cPos + cMargin,
y:Math.random() * cPos + cMargin,
vx:Math.random() * cSpeed + .25,
vy:Math.random() * cSpeed + .25
});
}
// ---- DRAW ---- //
requestAnimationFrame(draw);
function draw(){
c.fillStyle = 'white';
c.fillRect(container.x, container.y, container.width, container.height);
for (var i = 0; i < circles.length; i++){
/*var img = new Image();
var path = circles[i].image;*/
/*var size = circles[i].r * 2;*/
/*img.src = circles[4].image;*/
var img = activeLogo[i];
img.onload = function (circles) {
/*c.drawImage(img, 0, 0, size, size);*/
var pattern = c.createPattern(this, "repeat");
c.fillStyle = pattern;
c.fill();
};
c.fillStyle = 'hsl(' + circles[i].color + ', 100%, 50%)';
c.beginPath();
c.arc(circles[i].x, circles[i].y, circles[i].r, 0, 2*Math.PI, false);
c.fill();
// If the circle size/position is greater than the canvas width, bounce x
if ((circles[i].x + circles[i].vx + circles[i].r > container.width) || (circles[i].x - circles[i].r + circles[i].vx < container.x)) {
circles[i].vx = -circles[i].vx;
}
// If the circle size/position is greater than the canvas width, bounce y
if ((circles[i].y + circles[i].vy + circles[i].r > container.height) || (circles[i].y - circles[i].r + circles[i].vy < container.y)){
circles[i].vy = -circles[i].vy;
}
// Generates circle motion by adding position and velocity each frame
circles[i].x += circles[i].vx;
circles[i].y += circles[i].vy;
}
requestAnimationFrame(draw);
}
}
The way it works right now is:
1. I have my portfolio content set to "display: none" (eventually it will be a pop-up when they click on one of the circles).
2. The canvas is getting the portfolio objects from the DOM, including the image that I can't get to work.
3. If I use the "onload()" function, I can get the images to show up and repeat in the background. But it's just a static background - the circles are moving above it and revealing the background. That isn't what I want.
So basically, I'm trying to figure out how to attach the background image to the circle (based on the circle ID).
----------------- UPDATE -----------------
I can now clip the image to a circle and get the circle to move in the background. But it isn't visible on the page (I can tell it's moving by console logging it's position). The only time I see anything is when the circle lines up with the images position, then it shows.
function runAnimation(width, height, type){
var canvas = document.getElementsByTagName('canvas')[0];
var c = canvas.getContext("2d");
canvas.width = width;
canvas.height = height;
// Collects portfolio information from the DOM
var activeName = [];
var activeLogo = [];
$('.active').map(function() {
var text = $(this).text().replace(/\s+/g, '-').toLowerCase();
var elem = document.getElementsByClassName(text);
activeName.push(text);
activeLogo.push(elem[0].childNodes[0]);
});
var img = new Image();
img.onload = start;
var circles = [];
var cPos = 200;
var cMargin = 70;
var cSpeed = 3;
for (var i = 0; i < 1; i++) {
circles.push({
id: activeName[i],
img: activeLogo[i],
size: 50,
xPos: Math.random() * cPos + cMargin,
yPos: Math.random() * cPos + cMargin,
xVel: Math.random() * cSpeed + .25,
yVel: Math.random() * cSpeed + .25,
});
img.src = circles[i].img;
}
requestAnimationFrame(start);
function start(){
for (var i = 0; i < circles.length; i++) {
var circle = createImageInCircle(circles[i].img, circles[i].size, circles[i].xPos, circles[i].yPos);
c.drawImage(circle, circles[i].size, circles[i].size);
animateCircle(circles[i]);
}
requestAnimationFrame(start);
}
function createImageInCircle(img, radius, x, y){
var canvas2 = document.createElement('canvas');
var c2 = canvas2.getContext('2d');
canvas2.width = canvas2.height = radius*2;
c2.fillStyle = 'white';
c2.beginPath();
c2.arc(x, y, radius, 0, Math.PI*2);
c2.fill();
c2.globalCompositeOperation = 'source-atop';
c2.drawImage(img, 0, 0, 100, 100);
return(canvas2);
}
function animateCircle(circle) {
// If the circle size/position is greater than the canvas width, bounce x
if ((circle.xPos + circle.xVel + circle.size > canvas.width) || (circle.xPos - circle.size + circle.xVel < 0)) {
console.log('Bounce X');
circle.xVel = -circle.xVel;
}
// If the circle size/position is greater than the canvas width, bounce y
if ((circle.yPos + circle.yVel + circle.size > canvas.height) || (circle.yPos + circle.yVel - circle.size < 0)) {
console.log('Bounce Y');
circle.yVel = -circle.yVel;
}
// Generates circle motion by adding position and velocity each frame
circle.xPos += circle.xVel;
circle.yPos += circle.yVel;
}
}
I'm not sure if I'm animating the correct thing. I've tried animating canvas2, but that didn't make sense to me.
PS - Sorry for the GitHub formatting, not sure why it looks like that.
PPS - Apologies for any junk code I didn't clean up. I've tried a lot of stuff and probably lost track of some of the changes.
PPPS - And forgive me for not making the answer self-contained. I thought linking to GitHub would be more useful, but I've updated the question to contain all the necessary info. Thanks for the feedback.
To get you started...
Here's how to clip an image into a circle using compositing.
The example code creates a single canvas logo-ball that you can reuse for each of your bouncing balls.
var logoball1=dreateImageInCircle(logoImg1,50);
var logoball2=dreateImageInCircle(logoImg2,50);
Then you can draw each logo-ball onto your main canvas like this:
ctx.drawImage(logoball1,35,40);
ctx.drawImage(logoball2,100,75);
There are many examples here on Stackoverflow of how to animate the balls around the canvas so I leave that part to you.
var canvas=document.getElementById("canvas");
var ctx=canvas.getContext("2d");
var cw=canvas.width;
var ch=canvas.height;
var img=new Image();
img.onload=start;
img.src="https://dl.dropboxusercontent.com/u/139992952/m%26m600x455.jpg";
function start(){
var copy=createImageInCircle(img,50);
ctx.drawImage(copy,20,75);
ctx.drawImage(copy,150,120);
ctx.drawImage(copy,280,75);
}
function createImageInCircle(img,radius){
var c=document.createElement('canvas');
var cctx=c.getContext('2d');
c.width=c.height=radius*2;
cctx.beginPath();
cctx.arc(radius,radius,radius,0,Math.PI*2);
cctx.fill();
cctx.globalCompositeOperation='source-atop';
cctx.drawImage(img,radius-img.width/2,radius-img.height/2);
return(c);
}
body{ background-color:white; }
#canvas{border:1px solid red; }
<canvas id="canvas" width=512 height=512></canvas>
I'm trying to create a game in canvas with javascript where you control a spaceship and have it so that the canvas will translate and rotate to make it appear like the spaceship is staying stationary and not rotating.
Any help would be greatly appreciated.
window.addEventListener("load",eventWindowLoaded, false);
function eventWindowLoaded() {
canvasApp();
}
function canvasSupport() {
return Modernizr.canvas;
}
function canvasApp() {
if (!canvasSupport()) {
return;
}
var theCanvas = document.getElementById("myCanvas");
var height = theCanvas.height; //get the heigth of the canvas
var width = theCanvas.width; //get the width of the canvas
var context = theCanvas.getContext("2d"); //get the context
var then = Date.now();
var bgImage = new Image();
var stars = new Array;
bgImage.onload = function() {
context.translate(width/2,height/2);
main();
}
var rocket = {
xLoc: 0,
yLoc: 0,
score : 0,
damage : 0,
speed : 20,
angle : 0,
rotSpeed : 1,
rotChange: 0,
pointX: 0,
pointY: 0,
setScore : function(newScore){
this.score = newScore;
}
}
function Star(){
var dLoc = 100;
this.xLoc = rocket.pointX+ dLoc - Math.random()*2*dLoc;
this.yLoc = rocket.pointY + dLoc - Math.random()*2*dLoc;
//console.log(rocket.xLoc+" "+rocket.yLoc);
this.draw = function(){
drawStar(this.xLoc,this.yLoc,20,5,.5);
}
}
//var stars = new Array;
var drawStars = function(){
context.fillStyle = "yellow";
if (typeof stars !== 'undefined'){
//console.log("working");
for(var i=0;i< stars.length ;i++){
stars[i].draw();
}
}
}
var getDistance = function(x1,y1,x2,y2){
var distance = Math.sqrt(Math.pow((x2-x1),2)+Math.pow((y2-y1),2));
return distance;
}
var updateStars = function(){
var numStars = 10;
while(stars.length<numStars){
stars[stars.length] = new Star();
}
for(var i=0; i<stars.length; i++){
var tempDist = getDistance(rocket.pointX,rocket.pointY,stars[i].xLoc,stars[i].yLoc);
if(i == 0){
//console.log(tempDist);
}
if(tempDist > 100){
stars[i] = new Star();
}
}
}
function drawRocket(xLoc,yLoc, rWidth, rHeight){
var angle = rocket.angle;
var xVals = [xLoc,xLoc+(rWidth/2),xLoc+(rWidth/2),xLoc-(rWidth/2),xLoc-(rWidth/2),xLoc];
var yVals = [yLoc,yLoc+(rHeight/3),yLoc+rHeight,yLoc+rHeight,yLoc+(rHeight/3),yLoc];
for(var i = 0; i < xVals.length; i++){
xVals[i] -= xLoc;
yVals[i] -= yLoc+rHeight;
if(i == 0){
console.log(yVals[i]);
}
var tempXVal = xVals[i]*Math.cos(angle) - yVals[i]*Math.sin(angle);
var tempYVal = xVals[i]*Math.sin(angle) + yVals[i]*Math.cos(angle);
xVals[i] = tempXVal + xLoc;
yVals[i] = tempYVal+(yLoc+rHeight);
}
rocket.pointX = xVals[0];
rocket.pointY = yVals[0];
//rocket.yLoc = yVals[0];
//next rotate
context.beginPath();
context.moveTo(xVals[0],yVals[0])
for(var i = 1; i < xVals.length; i++){
context.lineTo(xVals[i],yVals[i]);
}
context.closePath();
context.lineWidth = 5;
context.strokeStyle = 'blue';
context.stroke();
}
var world = {
//pixels per second
startTime: Date.now(),
speed: 50,
startX:width/2,
startY:height/2,
originX: 0,
originY: 0,
xDist: 0,
yDist: 0,
rotationSpeed: 20,
angle: 0,
distance: 0,
calcOrigins : function(){
world.originX = -world.distance*Math.sin(world.angle*Math.PI/180);
world.originY = -world.distance*Math.cos(world.angle*Math.PI/180);
}
};
var keysDown = {};
addEventListener("keydown", function (e) {
keysDown[e.keyCode] = true;
}, false);
addEventListener("keyup", function (e) {
delete keysDown[e.keyCode];
}, false);
var update = function(modifier) {
if (37 in keysDown) { // Player holding left
rocket.angle -= rocket.rotSpeed* modifier;
rocket.rotChange = - rocket.rotSpeed* modifier;
//console.log("left");
}
if (39 in keysDown) { // Player holding right
rocket.angle += rocket.rotSpeed* modifier;
rocket.rotChange = rocket.rotSpeed* modifier;
//console.log("right");
}
};
var render = function (modifier) {
context.clearRect(-width*10,-height*10,width*20,height*20);
var dX = (rocket.speed*modifier)*Math.sin(rocket.angle);
var dY = (rocket.speed*modifier)*Math.cos(rocket.angle);
rocket.xLoc += dX;
rocket.yLoc -= dY;
updateStars();
drawStars();
context.translate(-dX,dY);
context.save();
context.translate(-rocket.pointX,-rocket.pointY);
context.translate(rocket.pointX,rocket.pointY);
drawRocket(rocket.xLoc,rocket.yLoc,50,200);
context.fillStyle = "red";
context.fillRect(rocket.pointX,rocket.pointY,15,5);
//context.restore(); // restores the coordinate system back to (0,0)
context.fillStyle = "green";
context.fillRect(0,0,10,10);
context.rotate(rocket.angle);
context.restore();
};
function drawStar(x, y, r, p, m)
{
context.save();
context.beginPath();
context.translate(x, y);
context.moveTo(0,0-r);
for (var i = 0; i < p; i++)
{
context.rotate(Math.PI / p);
context.lineTo(0, 0 - (r*m));
context.rotate(Math.PI / p);
context.lineTo(0, 0 - r);
}
context.fill();
context.restore();
}
// the game loop
function main(){
requestAnimationFrame(main);
var now = Date.now();
var delta = now - then;
update(delta / 1000);
//now = Date.now();
//delta = now - then;
render(delta / 1000);
then = now;
// Request to do this again ASAP
}
var w = window;
var requestAnimationFrame = w.requestAnimationFrame || w.webkitRequestAnimationFrame || w.msRequestAnimationFrame || w.mozRequestAnimationFrame;
//start the game loop
//gameLoop();
//event listenters
bgImage.src = "images/background.jpg";
} //canvasApp()
Origin
When you need to rotate something in canvas it will always rotate around origin, or center for the grid if you like where the x and y axis crosses.
You may find my answer here useful as well
By default the origin is in the top left corner at (0, 0) in the bitmap.
So in order to rotate content around a (x,y) point the origin must first be translated to that point, then rotated and finally (and usually) translated back. Now things can be drawn in the normal order and they will all be drawn rotated relative to that rotation point:
ctx.translate(rotateCenterX, rotateCenterY);
ctx.rotate(angleInRadians);
ctx.translate(-rotateCenterX, -rotateCenterY);
Absolute angles and positions
Sometimes it's easier to keep track if an absolute angle is used rather than using an angle that you accumulate over time.
translate(), transform(), rotate() etc. are accumulative methods; they add to the previous transform. We can set absolute transforms using setTransform() (the last two arguments are for translation):
ctx.setTransform(1, 0, 0, 1, rotateCenterX, rotateCenterY); // absolute
ctx.rotate(absoluteAngleInRadians);
ctx.translate(-rotateCenterX, -rotateCenterY);
The rotateCenterX/Y will represent the position of the ship which is drawn untransformed. Also here absolute transforms can be a better choice as you can do the rotation using absolute angles, draw background, reset transformations and then draw in the ship at rotateCenterX/Y:
ctx.setTransform(1, 0, 0, 1, rotateCenterX, rotateCenterY);
ctx.rotate(absoluteAngleInRadians);
ctx.translate(-rotateCenterX, -rotateCenterY);
// update scene/background etc.
ctx.setTransform(1, 0, 0, 1, 0, 0); // reset transforms
ctx.drawImage(ship, rotateCenterX, rotateCenterY);
(Depending on orders of things you could replace the first line here with just translate() as the transforms are reset later, see demo for example).
This allows you to move the ship around without worrying about current transforms, when a rotation is needed use the ship's current position as center for translation and rotation.
And a final note: the angle you would use for rotation would of course be the counter-angle that should be represented (ie. ctx.rotate(-angle);).
Space demo ("random" movements and rotations)
The red "meteors" are dropping in one direction (from top), but as the ship "navigates" around they will change direction relative to our top view angle. Camera will be fixed on the ship's position.
(ignore the messy part - it's just for the demo setup, and I hate scrollbars... focus on the center part :) )
var img = new Image();
img.onload = function() {
var ctx = document.querySelector("canvas").getContext("2d"),
w = 600, h = 400, meteors = [], count = 35, i = 0, x = w * 0.5, y, a = 0, a2 = 0;
ctx.canvas.width = w; ctx.canvas.height = h; ctx.fillStyle = "#555";
while(i++ < count) meteors.push(new Meteor());
(function loop() {
ctx.clearRect(0, 0, w, h);
y = h * 0.5 + 30 + Math.sin((a+=0.01) % Math.PI*2) * 60; // ship's y and origin's y
// translate to center of ship, rotate, translate back, render bg, reset, draw ship
ctx.translate(x, y); // translate to origin
ctx.rotate(Math.sin((a2+=0.005) % Math.PI) - Math.PI*0.25); // rotate some angle
ctx.translate(-x, -y); // translate back
ctx.beginPath(); // render some moving meteors for the demo
for(var i = 0; i < count; i++) meteors[i].update(ctx); ctx.fill();
ctx.setTransform(1, 0, 0, 1, 0, 0); // reset transforms
ctx.drawImage(img, x - 32, y); // draw ship as normal
requestAnimationFrame(loop); // loop animation
})();
};
function Meteor() { // just some moving object..
var size = 5 + 35 * Math.random(), x = Math.random() * 600, y = -200;
this.update = function(ctx) {
ctx.moveTo(x + size, y); ctx.arc(x, y, size, 0, 6.28);
y += size * 0.5; if (y > 600) y = -200;
};
}
img.src = "http://i.imgur.com/67KQykW.png?1";
body {background:#333} canvas {background:#000}
<canvas></canvas>
Good afternoon all,
I come to you with yet another request for a lesson/example/answers. While messing around with a canvas in HTML5, I have learned how to manipulate Depth(Z-Buffer) and several other neat things. However, now I am trying to find a way to perform Pathfinding with the canvas. Most of the examples on the Internet are a little difficult to comprehend for me due to the fact that they are handling pathfinding far differently than I am trying to achieve(Which is that they use tile based pathfinding). Most other examples seem to deal in boxes or rectangles as well.
This is my code that I used as an example to draw a Polygon:
var canvas = document.getElementById('CanvasPath');
var context = canvas.getContext('2d');
// begin custom shape
context.beginPath();
context.moveTo(170, 80);
context.bezierCurveTo(1, 200, 125, 230, 230, 150);
context.bezierCurveTo(250, 180, 320, 200, 340, 200);
context.bezierCurveTo(420, 150, 420, 120, 390, 100);
context.bezierCurveTo(430, 40, 370, 30, 340, 50);
context.bezierCurveTo(320, 5, 250, 20, 250, 50);
context.bezierCurveTo(200, 5, 150, 20, 170, 80);
context.closePath();
context.lineWidth = 2;
context.strokeStyle = 'gray';
context.stroke();
Lets say I have a small box that I want to move around in that Polygon(I really will be creating the polygon with line points rather than Bezier curvers. I just wantd to show an example here) when I click at the goal position I want it to be at... How can I create a pathfinding algorithm that will find its way around and yet not have the bottom points of the box touch outside the polygon? I am assuming I would need to get all the pixels that are in that polygon to create a path from? I am thinking that the Bezier Curves and points may need to be created and pushed from an Array instead and then find the path???
Any suggestions on approach and can you provide an example for how to go about this? Please be gentle... While I have been an experienced scripter and programmer, I have not been one to mess to much with games, or graphics and I am still learning to manipulate the canvas in HTML5. Thanks for your help in advance.
The key part of what you are asking is how to shrink a polygon so that your box can travel along the shrunken polygon without extending outside the original polygon.
The illustration below shows an original black polygon, a shrunken red polygon and a blue traveling box.
Precisely shrinking a polygon
The code to precisely shrink a polygon is quite complex. It involves repositioning the original polygon vertices based on whether each particular vertex forms a convex or concave angle.
Here's example code I derived from Hans Muller's Blog on Webkits Shape-Padding. This example requires that the polygon vertices defined in a clockwise order.
var canvas=document.getElementById("canvas");
var ctx=canvas.getContext("2d");
var cw=canvas.width;
var ch=canvas.height;
var shapePadding = 10;
var dragVertexIndex = null;
var hoverLocation = null;
var polygonVertexRadius = 9;
var polygon, marginPolygon, paddingPolygon;
var polygonVertices = [{x: 143, y: 327}, {x: 80, y: 236}, {x: 151, y: 148}, {x: 454, y: 69}, {x: 560, y: 320}];
var polygon = createPolygon(polygonVertices);
var paddingPolygon = createPaddingPolygon(polygon);
drawAll();
/////////////////////////////////
// Polygon creation and drawing
function drawAll(){
draw(polygon,'black');
draw(paddingPolygon,'red');
}
function draw(p,stroke){
var v=p.vertices;
ctx.beginPath();
ctx.moveTo(v[0].x,v[0].y);
for(var i=0;i<v.length;i++){
ctx.lineTo(v[i].x,v[i].y);
}
ctx.closePath();
ctx.strokeStyle=stroke;
ctx.stroke();
}
function createPolygon(vertices){
var polygon = {vertices: vertices};
var edges = [];
var minX = (vertices.length > 0) ? vertices[0].x : undefined;
var minY = (vertices.length > 0) ? vertices[0].y : undefined;
var maxX = minX;
var maxY = minY;
for (var i = 0; i < polygon.vertices.length; i++) {
vertices[i].label = String(i);
vertices[i].isReflex = isReflexVertex(polygon, i);
var edge = {
vertex1: vertices[i],
vertex2: vertices[(i + 1) % vertices.length],
polygon: polygon,
index: i
};
edge.outwardNormal = outwardEdgeNormal(edge);
edge.inwardNormal = inwardEdgeNormal(edge);
edges.push(edge);
var x = vertices[i].x;
var y = vertices[i].y;
minX = Math.min(x, minX);
minY = Math.min(y, minY);
maxX = Math.max(x, maxX);
maxY = Math.max(y, maxY);
}
polygon.edges = edges;
polygon.minX = minX;
polygon.minY = minY;
polygon.maxX = maxX;
polygon.maxY = maxY;
polygon.closed = true;
return polygon;
}
function createPaddingPolygon(polygon){
var offsetEdges = [];
for (var i = 0; i < polygon.edges.length; i++) {
var edge = polygon.edges[i];
var dx = edge.inwardNormal.x * shapePadding;
var dy = edge.inwardNormal.y * shapePadding;
offsetEdges.push(createOffsetEdge(edge, dx, dy));
}
var vertices = [];
for (var i = 0; i < offsetEdges.length; i++) {
var thisEdge = offsetEdges[i];
var prevEdge = offsetEdges[(i + offsetEdges.length - 1) % offsetEdges.length];
var vertex = edgesIntersection(prevEdge, thisEdge);
if (vertex)
vertices.push(vertex);
else {
var arcCenter = polygon.edges[i].vertex1;
appendArc(vertices, arcCenter, shapePadding, prevEdge.vertex2, thisEdge.vertex1, true);
}
}
var paddingPolygon = createPolygon(vertices);
paddingPolygon.offsetEdges = offsetEdges;
return paddingPolygon;
}
//////////////////////
// Support functions
function isReflexVertex(polygon, vertexIndex){
// Assuming that polygon vertices are in clockwise order
var thisVertex = polygon.vertices[vertexIndex];
var nextVertex = polygon.vertices[(vertexIndex + 1) % polygon.vertices.length];
var prevVertex = polygon.vertices[(vertexIndex + polygon.vertices.length - 1) % polygon.vertices.length];
if (leftSide(prevVertex, nextVertex, thisVertex) < 0){return true;} // TBD: return true if thisVertex is inside polygon when thisVertex isn't included
return false;
}
function inwardEdgeNormal(edge){
// Assuming that polygon vertices are in clockwise order
var dx = edge.vertex2.x - edge.vertex1.x;
var dy = edge.vertex2.y - edge.vertex1.y;
var edgeLength = Math.sqrt(dx*dx + dy*dy);
return {x: -dy/edgeLength, y: dx/edgeLength};
}
function outwardEdgeNormal(edge){
var n = inwardEdgeNormal(edge);
return {x: -n.x, y: -n.y};
}
// If the slope of line vertex1,vertex2 greater than the slope of vertex1,p then p is on the left side of vertex1,vertex2 and the return value is > 0.
// If p is colinear with vertex1,vertex2 then return 0, otherwise return a value < 0.
function leftSide(vertex1, vertex2, p){
return ((p.x - vertex1.x) * (vertex2.y - vertex1.y)) - ((vertex2.x - vertex1.x) * (p.y - vertex1.y));
}
function createOffsetEdge(edge, dx, dy){
return {
vertex1: {x: edge.vertex1.x + dx, y: edge.vertex1.y + dy},
vertex2: {x: edge.vertex2.x + dx, y: edge.vertex2.y + dy}
};
}
// based on http://local.wasp.uwa.edu.au/~pbourke/geometry/lineline2d/, edgeA => "line a", edgeB => "line b"
function edgesIntersection(edgeA, edgeB){
var den = (edgeB.vertex2.y - edgeB.vertex1.y) * (edgeA.vertex2.x - edgeA.vertex1.x) - (edgeB.vertex2.x - edgeB.vertex1.x) * (edgeA.vertex2.y - edgeA.vertex1.y);
if (den == 0){return null;} // lines are parallel or conincident
var ua = ((edgeB.vertex2.x - edgeB.vertex1.x) * (edgeA.vertex1.y - edgeB.vertex1.y) - (edgeB.vertex2.y - edgeB.vertex1.y) * (edgeA.vertex1.x - edgeB.vertex1.x)) / den;
var ub = ((edgeA.vertex2.x - edgeA.vertex1.x) * (edgeA.vertex1.y - edgeB.vertex1.y) - (edgeA.vertex2.y - edgeA.vertex1.y) * (edgeA.vertex1.x - edgeB.vertex1.x)) / den;
if (ua < 0 || ub < 0 || ua > 1 || ub > 1){ return null; }
return {x: edgeA.vertex1.x + ua * (edgeA.vertex2.x - edgeA.vertex1.x), y: edgeA.vertex1.y + ua * (edgeA.vertex2.y - edgeA.vertex1.y)};
}
function appendArc(vertices, center, radius, startVertex, endVertex, isPaddingBoundary){
const twoPI = Math.PI * 2;
var startAngle = Math.atan2(startVertex.y - center.y, startVertex.x - center.x);
var endAngle = Math.atan2(endVertex.y - center.y, endVertex.x - center.x);
if (startAngle < 0)
startAngle += twoPI;
if (endAngle < 0)
endAngle += twoPI;
var arcSegmentCount = 5; // An odd number so that one arc vertex will be eactly arcRadius from center.
var angle = ((startAngle > endAngle) ? (startAngle - endAngle) : (startAngle + twoPI - endAngle));
var angle5 = ((isPaddingBoundary) ? -angle : twoPI - angle) / arcSegmentCount;
vertices.push(startVertex);
for (var i = 1; i < arcSegmentCount; ++i) {
var angle = startAngle + angle5 * i;
var vertex = {
x: center.x + Math.cos(angle) * radius,
y: center.y + Math.sin(angle) * radius,
};
vertices.push(vertex);
}
vertices.push(endVertex);
}
body{ background-color: ivory; }
#canvas{border:1px solid red;}
<h4>Original black polygon and shrunken red polygon</h4>
<canvas id="canvas" width=650 height=400></canvas>
Calculating the waypoints along the polygon for your traveling box
To have your box travel along the inside of the polygon, you need an array containing points along each line of the polygon. You can calculate these points using linear interpolation.
Given an object defining a line like this:
var line={
x0:50,
y0:50,
x1:200,
y1:50};
You can use linear interpolation to calculate points along that line every 1px like this:
var allPoints = allLinePoints(line);
function allLinePoints(line){
var raw=[];
var dx = line.x1-line.x0;
var dy = line.y1-line.y0;
var length=Math.sqrt(dx*dx+dy*dy);
var segments=parseInt(length+1);
for(var i=0;i<segments;i++){
var percent=i/segments;
if(i==segments-1){
raw.push({x:line.x1,y:line.y1}); // force last point == p1
}else{
raw.push({ x:line.x0+dx*percent, y:line.y0+dy*percent});
}
}
return(raw);
}
Get the point on the polygon closest to the mouse click
You can use the distance formula (derived from Pythagorean theorem) to calculate which of the calculated waypoints is closest to the mouse click position:
// this will be the index in of the waypoint closest to the mouse
var indexOfClosestPoint;
// iterate all waypoints and find the closest to the mouse
var minLengthSquared=1000000*1000000;
for(var i=0;i<allPoints.length;i++){
var p=allPoints[i];
var dx=mouseX-p.x;
var dy=mouseY-p.y;
var dxy=dx*dx+dy*dy
if(dxy<minLengthSquared){
minLengthSquared=dxy;
indexOfClosestPoint=i;
}
}
Animate the box along each waypoint up to the calculated ending waypoint
The only thing left to do is set up an animation loop that redraws the traveling box at each waypoint along the polygon until it reaches the ending waypoint:
// start animating at the first waypoint
var animationIndex=0;
// use requestAnimationFrame to redraw the traveling box
// along each waypoint
function animate(time){
// redraw the line and the box at its current (percent) position
var pt=allPoints[animationIndex];
// redraw the polygon and the traveling box
ctx.strokeStyle='black';
ctx.lineWidth=1;
ctx.clearRect(0,0,cw,ch);
ctx.strokeStyle='black';
drawLines(linePoints);
ctx.strokeStyle='red';
drawLines(insideLinePoints);
ctx.fillStyle='skyblue';
ctx.fillRect(pt.x-boxWidth/2,pt.y-boxHeight/2,boxWidth,boxHeight);
// increase the percentage for the next frame loop
animationIndex++;
// Are we done?
if(animationIndex<=indexOfClosestPoint){
// request another frame loop
requestAnimationFrame(animate);
}else{
// set the flag indicating the animation is complete
isAnimating=false;
}
}
Here's what it looks like when you put it all together
var canvas=document.getElementById("canvas");
var ctx=canvas.getContext("2d");
var cw=canvas.width;
var ch=canvas.height;
function reOffset(){
var BB=canvas.getBoundingClientRect();
offsetX=BB.left;
offsetY=BB.top;
}
var offsetX,offsetY;
reOffset();
window.onscroll=function(e){ reOffset(); }
// polygon vertices
var polygonVertices=[
{x:143,y:327},
{x:80,y:236},
{x:151,y:148},
{x:454,y:69},
{x:560,y:320},
];
var shrunkenVertices=getShrunkenVertices(polygonVertices,10);
var polyPoints=getPolygonPoints(shrunkenVertices)
//log(shrunkenVertices);
// animation variables
var isAnimating=false;
var animationIndex=0;
//
var indexOfClosestPoint=-99;
// define the movable box
var boxWidth=12;
var boxHeight=10;
var boxRadius=Math.sqrt(boxWidth*boxWidth+boxHeight*boxHeight);
var boxFill='skyblue';
// listen for mouse events
$("#canvas").mousedown(function(e){handleMouseDown(e);});
$("#canvas").mousemove(function(e){handleMouseMove(e);});
drawPolys(polygonVertices,shrunkenVertices);
////////////////////////////
// animate box to endpoint
////////////////////////////
function animate(time){
ctx.clearRect(0,0,cw,ch);
drawPolys(polygonVertices,shrunkenVertices);
// redraw the line and the box at its current (percent) position
var pt=polyPoints[animationIndex];
ctx.fillStyle=boxFill;
ctx.fillRect(pt.x-boxWidth/2,pt.y-boxHeight/2,boxWidth,boxHeight);
// increase the percentage for the next frame loop
animationIndex++;
// request another frame loop
if(animationIndex<=indexOfClosestPoint){
requestAnimationFrame(animate);
}else{
isAnimating=false;
}
}
////////////////////////////////////
// select box endpoint with click
////////////////////////////////////
function handleMouseDown(e){
// return if we're already animating
if(isAnimating){return;}
// tell the browser we're handling this event
e.preventDefault();
e.stopPropagation();
// start animating
animationIndex=0;
isAnimating=true;
requestAnimationFrame(animate);
}
function handleMouseMove(e){
// return if we're already animating
if(isAnimating){return;}
// tell the browser we're handling this event
e.preventDefault();
e.stopPropagation();
// get mouse position
mouseX=parseInt(e.clientX-offsetX);
mouseY=parseInt(e.clientY-offsetY);
// find the nearest waypoint
indexOfClosestPoint=findNearestPointToMouse(mouseX,mouseY);
// redraw
ctx.clearRect(0,0,cw,ch);
drawPolys(polygonVertices,shrunkenVertices);
// draw a red dot at the nearest waypoint
drawDot(polyPoints[indexOfClosestPoint],'red');
}
function findNearestPointToMouse(mx,my){
// find the nearest waypoint
var minLengthSquared=1000000*1000000;
for(var i=0;i<polyPoints.length;i++){
var p=polyPoints[i];
var dx=mouseX-p.x;
var dy=mouseY-p.y;
var dxy=dx*dx+dy*dy
if(dxy<minLengthSquared){
minLengthSquared=dxy;
indexOfClosestPoint=i;
}
}
return(indexOfClosestPoint);
}
////////////////////////////////
// Drawing functions
////////////////////////////////
function drawPolys(polygon,shrunken){
drawPoly(polygon,'black');
drawPoly(shrunken,'blue');
}
function drawPoly(v,stroke){
ctx.beginPath();
ctx.moveTo(v[0].x,v[0].y);
for(var i=0;i<v.length;i++){
ctx.lineTo(v[i].x,v[i].y);
}
ctx.closePath();
ctx.strokeStyle=stroke;
ctx.stroke();
}
function drawDot(pt,color){
ctx.beginPath();
ctx.arc(pt.x,pt.y,3,0,Math.PI*2);
ctx.closePath();
ctx.fillStyle=color;
ctx.fill();
}
////////////////////////////////
// Get points along a polygon
////////////////////////////////
function getPolygonPoints(vertices){
// For this purpose, be sure to close the polygon
var v=vertices.slice(0);
var v0=v[0];
var vx=v[v.length-1];
if(v0.x!==vx.x || v0.y!==vx.y){v.push(v[0]);}
//
var points=[];
for(var i=1;i<v.length;i++){
var p0=v[i-1];
var p1=v[i];
var line={x0:p0.x,y0:p0.y,x1:p1.x,y1:p1.y};
points=points.concat(getLinePoints(line));
}
return(points);
}
function getLinePoints(line){
var raw=[];
var dx = line.x1-line.x0;
var dy = line.y1-line.y0;
var length=Math.sqrt(dx*dx+dy*dy);
var segments=parseInt(length+1);
for(var i=0;i<segments;i++){
var percent=i/segments;
if(i==segments-1){
raw.push({x:line.x1,y:line.y1}); // force last point == p1
}else{
raw.push({ x:line.x0+dx*percent, y:line.y0+dy*percent});
}
}
return(raw);
}
/////////////////////////
// "shrink" a polygon
/////////////////////////
function getShrunkenVertices(vertices,shapePadding){
var polygon = createPolygon(polygonVertices);
var paddingPolygon = createPaddingPolygon(polygon,shapePadding);
return(paddingPolygon.vertices);
}
function createPolygon(vertices){
var polygon = {vertices: vertices};
var edges = [];
var minX = (vertices.length > 0) ? vertices[0].x : undefined;
var minY = (vertices.length > 0) ? vertices[0].y : undefined;
var maxX = minX;
var maxY = minY;
for (var i = 0; i < polygon.vertices.length; i++) {
vertices[i].label = String(i);
vertices[i].isReflex = isReflexVertex(polygon, i);
var edge = {
vertex1: vertices[i],
vertex2: vertices[(i + 1) % vertices.length],
polygon: polygon,
index: i
};
edge.outwardNormal = outwardEdgeNormal(edge);
edge.inwardNormal = inwardEdgeNormal(edge);
edges.push(edge);
var x = vertices[i].x;
var y = vertices[i].y;
minX = Math.min(x, minX);
minY = Math.min(y, minY);
maxX = Math.max(x, maxX);
maxY = Math.max(y, maxY);
}
polygon.edges = edges;
polygon.minX = minX;
polygon.minY = minY;
polygon.maxX = maxX;
polygon.maxY = maxY;
polygon.closed = true;
return polygon;
}
function createPaddingPolygon(polygon,shapePadding){
var offsetEdges = [];
for (var i = 0; i < polygon.edges.length; i++) {
var edge = polygon.edges[i];
var dx = edge.inwardNormal.x * shapePadding;
var dy = edge.inwardNormal.y * shapePadding;
offsetEdges.push(createOffsetEdge(edge, dx, dy));
}
var vertices = [];
for (var i = 0; i < offsetEdges.length; i++) {
var thisEdge = offsetEdges[i];
var prevEdge = offsetEdges[(i + offsetEdges.length - 1) % offsetEdges.length];
var vertex = edgesIntersection(prevEdge, thisEdge);
if (vertex)
vertices.push(vertex);
else {
var arcCenter = polygon.edges[i].vertex1;
appendArc(vertices, arcCenter, shapePadding, prevEdge.vertex2, thisEdge.vertex1, true);
}
}
var paddingPolygon = createPolygon(vertices);
paddingPolygon.offsetEdges = offsetEdges;
return paddingPolygon;
}
function isReflexVertex(polygon, vertexIndex){
// Assuming that polygon vertices are in clockwise order
var thisVertex = polygon.vertices[vertexIndex];
var nextVertex = polygon.vertices[(vertexIndex + 1) % polygon.vertices.length];
var prevVertex = polygon.vertices[(vertexIndex + polygon.vertices.length - 1) % polygon.vertices.length];
if (leftSide(prevVertex, nextVertex, thisVertex) < 0){return true;} // TBD: return true if thisVertex is inside polygon when thisVertex isn't included
return false;
}
function inwardEdgeNormal(edge){
// Assuming that polygon vertices are in clockwise order
var dx = edge.vertex2.x - edge.vertex1.x;
var dy = edge.vertex2.y - edge.vertex1.y;
var edgeLength = Math.sqrt(dx*dx + dy*dy);
return {x: -dy/edgeLength, y: dx/edgeLength};
}
function outwardEdgeNormal(edge){
var n = inwardEdgeNormal(edge);
return {x: -n.x, y: -n.y};
}
// If the slope of line vertex1,vertex2 greater than the slope of vertex1,p then p is on the left side of vertex1,vertex2 and the return value is > 0.
// If p is colinear with vertex1,vertex2 then return 0, otherwise return a value < 0.
function leftSide(vertex1, vertex2, p){
return ((p.x - vertex1.x) * (vertex2.y - vertex1.y)) - ((vertex2.x - vertex1.x) * (p.y - vertex1.y));
}
function createOffsetEdge(edge, dx, dy){
return {
vertex1: {x: edge.vertex1.x + dx, y: edge.vertex1.y + dy},
vertex2: {x: edge.vertex2.x + dx, y: edge.vertex2.y + dy}
};
}
// based on http://local.wasp.uwa.edu.au/~pbourke/geometry/lineline2d/, edgeA => "line a", edgeB => "line b"
function edgesIntersection(edgeA, edgeB){
var den = (edgeB.vertex2.y - edgeB.vertex1.y) * (edgeA.vertex2.x - edgeA.vertex1.x) - (edgeB.vertex2.x - edgeB.vertex1.x) * (edgeA.vertex2.y - edgeA.vertex1.y);
if (den == 0){return null;} // lines are parallel or conincident
var ua = ((edgeB.vertex2.x - edgeB.vertex1.x) * (edgeA.vertex1.y - edgeB.vertex1.y) - (edgeB.vertex2.y - edgeB.vertex1.y) * (edgeA.vertex1.x - edgeB.vertex1.x)) / den;
var ub = ((edgeA.vertex2.x - edgeA.vertex1.x) * (edgeA.vertex1.y - edgeB.vertex1.y) - (edgeA.vertex2.y - edgeA.vertex1.y) * (edgeA.vertex1.x - edgeB.vertex1.x)) / den;
if (ua < 0 || ub < 0 || ua > 1 || ub > 1){ return null; }
return {x: edgeA.vertex1.x + ua * (edgeA.vertex2.x - edgeA.vertex1.x), y: edgeA.vertex1.y + ua * (edgeA.vertex2.y - edgeA.vertex1.y)};
}
function appendArc(vertices, center, radius, startVertex, endVertex, isPaddingBoundary){
const twoPI = Math.PI * 2;
var startAngle = Math.atan2(startVertex.y - center.y, startVertex.x - center.x);
var endAngle = Math.atan2(endVertex.y - center.y, endVertex.x - center.x);
if (startAngle < 0)
startAngle += twoPI;
if (endAngle < 0)
endAngle += twoPI;
var arcSegmentCount = 5; // An odd number so that one arc vertex will be eactly arcRadius from center.
var angle = ((startAngle > endAngle) ? (startAngle - endAngle) : (startAngle + twoPI - endAngle));
var angle5 = ((isPaddingBoundary) ? -angle : twoPI - angle) / arcSegmentCount;
vertices.push(startVertex);
for (var i = 1; i < arcSegmentCount; ++i) {
var angle = startAngle + angle5 * i;
var vertex = {
x: center.x + Math.cos(angle) * radius,
y: center.y + Math.sin(angle) * radius,
};
vertices.push(vertex);
}
vertices.push(endVertex);
}
/////////////////////////
// End "shrink polygon"
/////////////////////////
body{ background-color: ivory; }
#canvas{border:1px solid red;}
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.9.1/jquery.min.js"></script>
<h4>Move mouse to where you want the box to end up<br>Then click to start the box animating from start to end.<br>Note: The starting point is on the bottom left of the polygon</h4>
<canvas id="canvas" width=650 height=400></canvas>
Using curved paths
If you want to make your closed path with Bezier curves, you will have to calculate waypoints along the curves using De Casteljau's algorithm. You will want to over-sample the number of points--maybe 500 values of T between 0.00 and 1.00. Here is a javascript version of the algorithm that calculates x,y points at interval T along a Cubic Bezier Curve:
// De Casteljau's algorithm which calculates points along a cubic Bezier curve
// plot a point at interval T along a bezier curve
// T==0.00 at beginning of curve. T==1.00 at ending of curve
// Calculating 300 T's between 0-1 will usually define the curve sufficiently
function getCubicBezierXYatT(startPt,controlPt1,controlPt2,endPt,T){
var x=CubicN(T,startPt.x,controlPt1.x,controlPt2.x,endPt.x);
var y=CubicN(T,startPt.y,controlPt1.y,controlPt2.y,endPt.y);
return({x:x,y:y});
}
// cubic helper formula at T distance
function CubicN(T, a,b,c,d) {
var t2 = T * T;
var t3 = t2 * T;
return a + (-a * 3 + T * (3 * a - a * T)) * T
+ (3 * b + T * (-6 * b + b * 3 * T)) * T
+ (c * 3 - c * 3 * T) * t2
+ d * t3;
}