Develop Reference

Problem with Khan Academy Challenge - Hovering over a button is inconsistent

I'm working my way through the Khan Academy advanced JS and I've encountered what I feel should be a simple problem, but I've just gotten entirely stuck on it. I'm working on a memory tile game, trying to add some extra features.
I'm trying to change the stroke colour of an object when the mouse is over it - I've included this as a prototype in each 'tile' object and this check is performed during the draw function - so every frame.
The stroke colour does change as I wanted it to, but stops working once I 'flip up' a couple of the tiles and they flip back down, the hover effect stops working. It now works only when a single tile is flipped up.
I can't figure out why the 'face up' variable in the tile object would be affecting the hover check - I feel I'm missing something obvious but for the life of me can't see it.
I've looked at some similar projects and their button highlighting, they seem to do exactly the same thing as me.
The Tile Object -
var Tile = function(x, y, face) {
this.x = x;
this.y = y;
this.size = 70;
this.face = face;
this.isFaceUp = false;
this.isMatch = false;
};
Tile.prototype.draw = function() {
this.hover();
fill(214, 247, 202);
strokeWeight(2);
rect(this.x, this.y, this.size, this.size, 10);
if (this.isFaceUp) {
image(this.face, this.x, this.y, this.size, this.size);
} else {
image(getImage("avatars/leaf-green"), this.x, this.y, this.size, this.size);
}
};
//Mouse Hover code - only works one time for some reason. After flipping back this stops working for some reason.
Tile.prototype.hover = function() {
stroke(0, 0, 0);
if (this.isMouseInside()){
stroke(7, 122, 44);
}
};
Tile.prototype.isUnderMouse = function(x, y) {
return x >= this.x && x <= this.x + this.size &&
y >= this.y && y <= this.y + this.size;
};
//check if mouse cursor is inside the tile
Tile.prototype.isMouseInside = function() {
return mouseX > this.x &&
mouseX < (this.x + this.size) &&
mouseY > this.y &&
mouseY < (this.y + this.size) &&
this.isFaceUp === false;
};
The Mouse Clicked Function - prewritten by KA
mouseClicked = function() {
for (var i = 0; i < tiles.length; i++) {
var tile = tiles[i];
if (tile.isUnderMouse(mouseX, mouseY)) {
if (flippedTiles.length < 2 && !tile.isFaceUp) {
tile.isFaceUp = true;
flippedTiles.push(tile);
if (flippedTiles.length === 2) {
numTries++;
if (flippedTiles[0].face === flippedTiles[1].face) {
flippedTiles[0].isMatch = true;
flippedTiles[1].isMatch = true;
flippedTiles.length = 0;
numMatches++;
}
delayStartFC = frameCount;
}
}
loop();
}
}
};
The Draw function - prewritten by KA
draw = function() {
background(255, 255, 255);
if (delayStartFC && (frameCount - delayStartFC) > 30) {
for (var i = 0; i < tiles.length; i++) {
var tile = tiles[i];
if (!tile.isMatch) {
tile.isFaceUp = false;
}
}
flippedTiles = [];
delayStartFC = null;
noLoop();
}
for (var i = 0; i < tiles.length; i++) {
tiles[i].draw();
}
if (numMatches === tiles.length/2) {
fill(0, 0, 0);
textSize(20);
text("You found them all in " + numTries + " tries!", 20, 375);
}
};
noLoop();

It drove me nuts trying to work out a function for mouse over then it hit me, my solution to change the stroke weight on rollover. in the Tile.prototype.draw function add:
if (this.isUnderMouse(mouseX, mouseY)){
strokeWeight(5);
}
else {
strokeWeight(2);
}

HTML Canvas & JavaScript - Redefining Object on Selection

The script below draws an image on the left side of the screen and a selection box in the right. It then attempts to redefine the image drawn on the left on each new selection in the selection box on the right by making the imageID dependent on the selection. However, as you can see below, whatever number you select on the right the image remains the same (1) because whilst it might be redrawn, it is not redefined on selection. What I would like to happen is that on selection in the box on the right the number in the image changes with the selection box such that it always correlates with the selection. In other words, when you click on 2 the image changes to the 2nd image in images. I have found two ways of doing this but they are both flawed:
1: Define img in paint's render function. This works but it makes everything run very slowly and the hover animations on the image stop working as expected.
2: Define img in the makeSelectionInfo function. This also works but the hover animations completely stop working if this is done.
I apologise for the long code but I couldn't condense it any more. For the sake of brevity I have only included images for numbers between 1 & 5. Any help will be appreciated.
var c=document.getElementById('game'),
canvasX=c.offsetLeft,
canvasY=c.offsetTop,
ctx=c.getContext('2d');
images=['https://i.stack.imgur.com/KfN4z.jpg',
'https://i.stack.imgur.com/MyQS1.png',
'https://i.stack.imgur.com/3Vlfj.jpg',
'https://i.stack.imgur.com/u3NLH.jpg',
'https://i.stack.imgur.com/XnLwl.png'];
var curvedRect = function(text, x, y, w, h) {
this.text = text;
this.x = x;
this.y = y;
this.w = w;
this.h = h;
this.hovered = false;
this.clicked = false;
}
curvedRect.prototype.makeCurvedRect = function() {
var delta=0, theta=0, yRotation=this.y;
if (this.hovered) {
delta = 3;
shadowColor = '#000000';
shadowBlur = 20;
shadowOffsetX = 5;
shadowOffsetY = 5;
theta = -0.01;
} else {
delta = 0;
theta = 0;
shadowColor = '#9F3A9B';
shadowBlur = 0;
shadowOffsetX = 0;
shadowOffsetY = 0;
}
var x = this.x-delta;
var y = yRotation-delta;
var w = this.w+(2*delta);
var h = this.h+(2*delta);
var img=new Image();
img.src=images[this.text];
ctx.rotate(theta);
ctx.beginPath();
ctx.lineWidth='8';
ctx.strokeStyle='white';
ctx.moveTo(x+10, y);
ctx.lineTo(x+w-10, y);
ctx.quadraticCurveTo(x+w, y, x+w, y+10);
ctx.lineTo(x+w, y+h-10);
ctx.quadraticCurveTo(x+w, y+h, x+w-10, y+h);
ctx.lineTo(x+10, y+h);
ctx.quadraticCurveTo(x, y+h, x, y+h-10);
ctx.lineTo(x, y+10);
ctx.quadraticCurveTo(x, y, x+10, y);
ctx.shadowColor = shadowColor;
ctx.shadowBlur = shadowBlur;
ctx.shadowOffsetX = shadowOffsetX;
ctx.shadowOffsetY = shadowOffsetY;
ctx.stroke();
ctx.shadowBlur = 0;
ctx.shadowOffsetX = 0;
ctx.shadowOffsetY = 0;
ctx.drawImage(img, x+2.5, y+2.5, w-5, h-5);
ctx.rotate(-theta);
}
curvedRect.prototype.hitTest = function(x, y) {
return (x >= this.x) && (x <= (this.w+this.x)) && (y >= this.y) && (y <= (this.h+this.y));
}
var selectionForMenu = function(id, text, y) {
this.id = id;
this.text = text;
this.y = y;
this.hovered = false;
this.clicked = false;
this.lastClicked = false;
}
function makeTextForSelected(text, y) {
ctx.font='bold 12px Noto Sans';
ctx.fillStyle='white';
ctx.textAlign='center';
ctx.fillText(text, 200, y);
}
function makeSelectionInfo(text) {
makeTextForSelected(text, 375);
}
selectionForMenu.prototype.makeSelection = function() {
var fillColor='#A84FA5';
if (this.hovered) {
if (this.clicked) {
if (this.lastClicked) {
fillColor='#E4C7E2';
} else {
fillColor='#D5A9D3';
}
} else if (this.lastClicked) {
fillColor='#D3A4D0';
makeSelectionInfo(this.text);
} else {
fillColor='#BA74B7';
}
} else if (this.lastClicked) {
fillColor='#C78DC5';
makeSelectionInfo(this.text);
} else {
fillColor='#A84FA5';
}
ctx.beginPath();
ctx.fillStyle=fillColor;
ctx.fillRect(400, this.y, 350, 30)
ctx.stroke();
ctx.font='10px Noto Sans';
ctx.fillStyle='white';
ctx.textAlign='left';
ctx.fillText(this.text, 410, this.y+19);
}
selectionForMenu.prototype.hitTest = function(x, y) {
return (x >= 400) && (x <= (750)) && (y >= this.y) && (y <= (this.y+30)) && !((x >= 400) && (y > 450));
}
var Paint = function(element) {
this.element = element;
this.shapes = [];
}
Paint.prototype.addShape = function(shape) {
this.shapes.push(shape);
}
Paint.prototype.render = function() {
ctx.clearRect(0, 0, this.element.width, this.element.height);
for (var i=0; i<this.shapes.length; i++) {
try {
this.shapes[i].makeSelection();
}
catch(err) {}
try {
this.shapes[i].makeCurvedRect();
}
catch(err) {}
}
ctx.beginPath();
ctx.fillStyle='white';
ctx.fillRect(0, 0, 750, 25);
ctx.stroke();
for (var i=0; i<this.shapes.length; i++) {
try {
this.shapes[i].makeBox();
}
catch(err) {}
}
ctx.beginPath();
ctx.fillStyle='#BC77BA';
ctx.fillRect(0, 450, 750, 50);
ctx.stroke();
ctx.font='bold 10px Noto Sans';
ctx.fillStyle='#9F3A9B';
ctx.textAlign='center';
ctx.fillText('Phrase Practice', 365, 17);
for (var i=0; i<this.shapes.length; i++) {
try {
this.shapes[i].makeInteractiveButton();
}
catch(err) {}
}
}
Paint.prototype.setHovered = function(shape) {
for (var i=0; i<this.shapes.length; i++) {
this.shapes[i].hovered = this.shapes[i] == shape;
}
this.render();
}
Paint.prototype.setClicked = function(shape) {
for (var i=0; i<this.shapes.length; i++) {
this.shapes[i].clicked = this.shapes[i] == shape;
}
this.render();
}
Paint.prototype.setUnclicked = function(shape) {
for (var i=0; i<this.shapes.length; i++) {
if (shape.constructor.name==this.shapes[i].constructor.name) {
this.shapes[i].clicked = false;
if (shape instanceof selectionForMenu) {
this.shapes[i].lastClicked = this.shapes[i] == shape;
}
}
}
this.render();
}
Paint.prototype.select = function(x, y) {
for (var i=this.shapes.length-1; i >= 0; i--) {
if (this.shapes[i].hitTest(x, y)) {
return this.shapes[i];
}
}
return null
}
imageID = 0;
var paint = new Paint(c);
var img = new curvedRect(imageID, 112.5, 100, 175, 175);
var selection = [];
for (i=0; i<=30; i++) {
selection.push(new selectionForMenu(i, i, 25+(i*30)));
}
paint.addShape(img);
for (i=0; i<30; i++) {
paint.addShape(selection[i])
}
paint.render();
var clickedShape=0;
var i=0;
function mouseDown(event) {
var x = event.x - canvasX;
var y = event.y - canvasY;
var shape = paint.select(x, y);
if (shape instanceof selectionForMenu) {
imageTextID = shape.id;
if (i==0) {
clickedShape=shape;
i=1;
} else if (i==1) {
i=0;
}
}
paint.setClicked(shape);
}
function mouseUp(event) {
var x = event.x - canvasX;
var y = event.y - canvasY;
var shape = paint.select(x, y);
if (clickedShape instanceof selectionForMenu) {
if (x>400 && y>25 && y<450) {
paint.setUnclicked(shape);
} else if (shape && !(shape instanceof selectionForMenu)) {
paint.setUnclicked(shape);
}
}
}
function mouseMove(event) {
var x = event.x - canvasX;
var y = event.y - canvasY;
var shape = paint.select(x, y);
paint.setHovered(shape);
}
c.addEventListener('mousedown', mouseDown);
c.addEventListener('mouseup', mouseUp);
c.addEventListener('mousemove', mouseMove);
canvas {
z-index: -1;
margin: 1em auto;
border: 1px solid black;
display: block;
background: #9F3A9B;
}
<!doctype html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>uTalk Demo</title>
</head>
<body>
<canvas id="game" width = "750" height = "500"></canvas>
</body>
</html>

Fixed your code here https://jsfiddle.net/0wq0hked/2/
You can diff to see what I changed, but basically you weren't initializing and adding the multiple curvedRect to the Paint.shapes array. I also added the images as an attribute of curvedRect.
I also had to add a visible parameter to your shapes, as your mouse hover Paint.select function was not functioning properly. The way yours works, shapes that share the same (x,y) do not allow other shapes from being hovered even when they are not visible. Thus multiple shapes occupying the image area to the left stopped the hover from working properly. I suppose you could keep your Paint.select and instance/remove shapes when they are to be drawn, but you do not have shape removal functionality as far as I can tell.
Also, you call render on every event, this is a bad idea. Take a look at requestAnimationFrame and try drawing at the screen refresh rate rather than on user input.

Why isnt collision detection working? (p5 js frame work)

I created a collision detection between Snake and BasicEnemy. I created a for loop to make five different enemies but the collision detection doesn't get called on any of the enemies that were created from the for loop. The collision only works with the one BasicEnemy object. Why isn't collision function being called for all of the enemies inside the array? Thank you.
Sketch.js
var snake;
var food;
var basicEnemy;
var scl = 20;
var enemies = [];
function setup() {
createCanvas(600, 500);
snake = new Snake();
basicEnemy = new BasicEnemy();
//** CREATE FIVE ENEMIES **
for (var i = 0; i < 5; i++) {
enemies[i] = new BasicEnemy();
}
}
// **FUNCTION WHEN SNAKE HITS ENEMY**
function collision() {
console.log("hit!");
}
function draw() {
background(51);
//Draw snake
snake.update();
snake.show();
//Draw basicEnemy
basicEnemy.update();
basicEnemy.show();
//** LOOP THROUGH ENEMIES AND UPDATE AND SHOW **
for (var i = 0; i < enemies.length; i++) {
enemies[i].show();
enemies[i].update();
if (enemies[i].hits(snake)) {
collision();
}
}
}
function keyPressed() {
if (keyCode === UP_ARROW){
snake.dir(0, -1);
} else if (keyCode === DOWN_ARROW) {
snake.dir(0, 1);
} else if (keyCode === LEFT_ARROW) {
snake.dir(-1 , 0);
} else if (keyCode === RIGHT_ARROW) {
snake.dir(1 , 0);
}
}
BasicEnemy.js
function BasicEnemy() {
this.x = random(700);
this.y = random(700);
this.velX = 15;
this.velY = 15;
}
//** FUNCTION TO CHECK IF ENEMY AND SNAKE ARE IN THE SAME LOCATION **
this.hits = function (pos) {
var = d = dist(this.x, this.y, pos.x, pos.y);
if(d < 1) {
return true;
} else {
return false;
}
}
this.show = function () {
fill(255, 0, 100);
rect(this.x, this.y, scl, scl);
}
Snake.js
function Snake() {
this.x = 0;
this.y = 0;
this.xspeed = 1;
this.yspeed = 0;
this.update = function() {
this.x = this.x + this.xspeed * scl;
this.y = this.y + this.yspeed * scl;
this.x = constrain(this.x, 0, width - scl);
this.y = constrain(this.y, 0, height - scl);
}
this.show = function() {
fill(255);
rect(this.x, this.y, scl, scl);
}
this.dir = function (x , y) {
this.xspeed = x;
this.yspeed = y;
}
}

Because you're essentially checking for the distance between the top left corners of the snake and the enemy, this'll only return true, if they completely overlap.
Use an AABB collision detection instead:
return this.x + scl >= pos.x && this.x <= pos.x + scl && this.y + scl >= pos.y && this.y <= pos.y + scl;
This returns true, if the first rectangle contains the second rectangle.
MDN says:
One of the simpler forms of collision detection is between two rectangles that are axis aligned — meaning no rotation. The algorithm works by ensuring there is no gap between any of the 4 sides of the rectangles. Any gap means a collision does not exist.

Canvas collision

I am a new in javascript and trying to find out how to make a collision with ball and plank which will stop the game and alert player with something like "You lost". But I only want red balls to hit the plank and blue to pass on without touching. Here is code that I am working on. (I dont mind if you could help to do collision only with both balls)
var spawnRate = 100;
var spawnRateOfDescent = 2;
var lastSpawn = -10;
var objects = [];
var startTime = Date.now();
function spawnRandomObject() {
var t;
if (Math.random() < 0.50) {
t = "red";
} else {
t = "blue";
}
var object = {
type: t,
x: Math.random() * (canvas.width - 30) + 15,
y: 0
}
objects.push(object);
}
function animate() {
var time = Date.now();
if (time > (lastSpawn + spawnRate)) {
lastSpawn = time;
spawnRandomObject();
}
for (var i = 0; i < objects.length; i++) {
var object = objects[i];
object.y += spawnRateOfDescent;
ctx.beginPath();
ctx.arc(object.x, object.y, 8, 0, Math.PI * 2);
ctx.closePath();
ctx.fillStyle = object.type;
ctx.fill();
}
}
var canvas = document.getElementById("myCanvas");
var ctx = canvas.getContext("2d");
var paddleHeight = 10;
var paddleWidth = 60;
var paddleY = 480
var paddleX = (canvas.width-paddleWidth)/2;
var rightPressed = false;
var leftPressed = false;
document.addEventListener("keydown", keyDownHandler, false);
document.addEventListener("keyup", keyUpHandler, false);
function keyDownHandler(e) {
if(e.keyCode == 39) {
rightPressed = true;
}
else if(e.keyCode == 37) {
leftPressed = true;
}
}
function keyUpHandler(e) {
if(e.keyCode == 39) {
rightPressed = false;
}
else if(e.keyCode == 37) {
leftPressed = false;
}
}
function drawPaddle() {
ctx.beginPath();
ctx.rect(paddleX, paddleY, paddleWidth, paddleHeight);
ctx.fillStyle = "#0095DD";
ctx.fill();
ctx.closePath();
}
function draw() {
ctx.clearRect(0, 0, canvas.width, canvas.height);
drawPaddle();
animate();
if(rightPressed && paddleX < canvas.width-paddleWidth) {
paddleX += 3;
}
else if(leftPressed && paddleX > 0) {
paddleX -= 3;
}
}
setInterval(draw, 10);
Thanks!

If you have an object like this:
let ball = { type: 'red', x: 10, y: 10, width: 10, height: 10 };
You might want to consider adding a method to this to check if it overlaps any other rectangle:
ball.overlapsBall = function( otherBall ){
return !(
otherBall.x + otherBall.width < this.x
&& otherBall.y + otherBall.height < this.y
&& otherBall.y > this.y + this.height
&& otherBall.x > this.x + this.height
);
}
You do this by checking if it does not overlap, which is only true if one box is entirely outside of the other (have a read through the if statement and try to visualise it, its actually rather simple)
In your draw function you could now add a loop to see if any overlap occurs:
var overlap = objects.filter(function( ball ) { return paddle.overlapsBall( ball ) });
You could even place an if statement to check it's type! (The filter will take you entire array of balls and check the overlaps, and remove anything from the array that does not return true. Now you can use overlaps.forEach(function( ball ){ /* ... */}); to do something with all the balls that overlapped your paddle.)
One last thing, if you are planning on doing this with many objects you might want to consider using a simple class like this for every paddle or ball you make:
class Object2D {
constructor(x = 0, y = 0;, width = 1, height = 1){
this.x = x;
this.y = x;
this.width = width;
this.height = height;
}
overlaps( otherObject ){
!( otherObject.x + otherObject.width < this.x && otherObject.y + otherObject.height < this.y && otherObject.y > this.y + this.height && otherObject.x > this.x + this.height );
}
}
This allows you to this simple expression to create a new object that automatically has a method to check for overlaps with similar objects:
var paddle = new Object2D(0,0,20,10);
var ball = new Object2D(5,5,10,10);
paddle.overlaps( ball ); // true!
On top of that, you are ensured that any Object2D contains the values you will need for your calculations. You can check if this object is if the right type using paddle instanceof Object2D (which is true).
Note Please note, as #Janje so continuously points out in the comments below, that we are doing a rectangle overlap here and it might create some 'false positives' for all the pieces of rectangle that aren't the circle. This is good enough for most cases, but you can find the math for other overlaps and collisions easily ith a quick google search.
Update: Simple Implementation
See below for a very simple example of how overlaps work in action:
var paddle = { x: 50, y: 50, width: 60, height: 20 };
var box = { x: 5, y: 20, width: 20, height: 20 };
var canvas = document.createElement('canvas');
var ctx = canvas.getContext('2d');
document.body.appendChild( canvas );
canvas.width = 300;
canvas.height = 300;
function overlaps( a, b ){
return !!( a.x + a.width > b.x && a.x < b.x + b.width
&& a.y + a.height > b.y && a.y < b.y + b.height );
}
function animate(){
ctx.clearRect( 0, 0, canvas.width, canvas.height );
ctx.fillStyle = overlaps( paddle, box ) ? "red" : "black";
ctx.fillRect( paddle.x, paddle.y, paddle.width, paddle.height );
ctx.fillRect( box.x, box.y, box.width, box.height );
window.requestAnimationFrame( animate );
}
canvas.addEventListener('mousemove', function(event){
paddle.x = event.clientX - paddle.width / 2;
paddle.y = event.clientY - paddle.height / 2;
})
animate();

New to JS, is there a way to turn these circles to diamonds?

As the titles suggests, I'm trying to get this blinking field of circles to rectangles or diamonds, whichever is easer really.
Link: http://jsfiddle.net/Jksb5/1/
HTML
<canvas id="pixie"></canvas>
JS
var WIDTH;
var HEIGHT;
var canvas;
var con;
var g;
var pxs = new Array();
var rint = 60;
$(document).ready(function(){
WIDTH = 960;
HEIGHT = 300;
canvas = document.getElementById('pixie');
$(canvas).attr('width', WIDTH).attr('height',HEIGHT);
con = canvas.getContext('2d');
for(var i = 0; i < 100; i++) {
pxs[i] = new Circle();
pxs[i].reset();
}
setInterval(draw,rint);
});
function draw() {
con.clearRect(0,0,WIDTH,HEIGHT);
for(var i = 0; i < pxs.length; i++) {
pxs[i].fade();
pxs[i].move();
pxs[i].draw();
}
}
function Circle() {
this.s = {ttl:8000, xmax:5, ymax:2, rmax:25, rt:1, xdef:90, ydef:90, xdrift:4, ydrift: 4, random:true, blink:true};
this.reset = function() {
this.x = (this.s.random ? WIDTH*Math.random() : this.s.xdef);
this.y = (this.s.random ? HEIGHT*Math.random() : this.s.ydef);
this.r = ((this.s.rmax-1)*Math.random()) + 1;
this.dx = (Math.random()*this.s.xmax) * (Math.random() < .5 ? -1 : 1);
this.dy = (Math.random()*this.s.ymax) * (Math.random() < .5 ? -1 : 1);
this.hl = (this.s.ttl/rint)*(this.r/this.s.rmax);
this.rt = Math.random()*this.hl;
this.s.rt = Math.random()+1;
this.stop = Math.random()*.2+.4;
this.s.xdrift *= Math.random() * (Math.random() < .5 ? -1 : 1);
this.s.ydrift *= Math.random() * (Math.random() < .5 ? -1 : 1);
}
this.fade = function() {
this.rt += this.s.rt;
}
this.draw = function() {
if(this.s.blink && (this.rt <= 0 || this.rt >= this.hl)) this.s.rt = this.s.rt*-1;
else if(this.rt >= this.hl) this.reset();
var newo = 1-(this.rt/this.hl);
con.beginPath();
con.arc(this.x,this.y,this.r,0,Math.PI*2,true);
// con.rect(188, 50, 100, 100);
con.closePath();
var cr = this.r*newo;
g = con.createRadialGradient(this.x,this.y,0,this.x,this.y,(cr <= 0 ? 1 : cr));
g.addColorStop(0.0, 'rgba(237,23,31,'+newo+')');
// g.addColorStop(this.stop, 'rgba(237,146,157,'+(newo*.6)+')');
g.addColorStop(1.0, 'rgba(126,22,40,0)');
con.fillStyle = g;
con.fill();
}
this.move = function() {
this.x += (this.rt/this.hl)*this.dx;
this.y += (this.rt/this.hl)*this.dy;
if(this.x > WIDTH || this.x < 0) this.dx *= -1;
if(this.y > HEIGHT || this.y < 0) this.dy *= -1;
}
this.getX = function() { return this.x; }
this.getY = function() { return this.y; }
}
One thing I've tried was to change the con.arc var to be a rectangle thinking that might be what's generating the circle, but when I comment that particular line it makes the field into a small rectangle, not the objects.
So I'm guessing what needs to be modified is the this function, which I really can't figure out/understand. Any help would be appreciated, thanks!

You can replace the arc call with
con.moveTo(this.x, this.y-this.r/2);
con.lineTo(this.x+this.r/2, this.y);
con.lineTo(this.x, this.y+this.r/2);
con.lineTo(this.x-this.r/2, this.y);
The gradient filling will of course remain round

con is a CanvasRenderingContext2D, which is what you use to draw on the canvas.
First, a path is created with
con.beginPath();
con.arc(this.x, this.y, this.r, 0, Math.PI * 2, true);
con.closePath();
This doesn't actually draw anything on the canvas, though. Nothing is drawn until the path is filled: con.fill().
What the lines before con.fill() do is create a gradient object and set it as the fillStyle, so it's drawn inside the circle when con.fill is called.
g = con.createRadialGradient(this.x, this.y, 0, this.x, this.y, (cr <= 0 ? 1 : cr));
g.addColorStop(0.0, 'rgba(237,23,31,' + newo + ')');
g.addColorStop(1.0, 'rgba(126,22,40,0)');
con.fillStyle = g;
If you remove those lines, con.rect will work. You can replace the circles with squares like this:
con.beginPath();
con.rect(this.x, this.y, this.r, this.r);
con.closePath();
con.fill();
It isn't as pretty, but it's a start.