How to make the ball appear in a random location - javascript

I have code that creates a ball and then gives it a random color. Not sure how to make the circle "spawn" in a random location on the screen.
var RADIUS = 120;
var circle;
function start(){
circle = new Circle(RADIUS);
circle.setPosition();
add(circle);
setTimer(color, 1000);
}
function color() {
circle.setColor(Randomizer.nextColor());
}

Here is a small example, hope you understand.
in your html:
in your script:
var canvas = document.getElementById("canvas_id");
var screen = canvas.getContext("2d");
function drawBall()
{
screen.beginPath();
screen.arc(x, y, ballRadius, 0, Math.PI*2);
screen.fillStyle = "#000000";
screen.fill();
screen.closePath();
}
Now just change the x and y respectively! Goodluck.

You could try possitionin with css
circle.style.position = "absolute";
circle.style.top = "580px";
circle.style.left = "205px";

This question is very old but figured I'd add my 2 cents in case someone lands here for the same question. To make the circle spawn at a random location onload, you would need to randomize the x and y variables. The aim of this is to avoid it spawning at the same place all the time thus making the game boring.
var x = Math.floor(Math.random() * canvas.width);
var y = Math.floor(Math.random() * canvas.height);
However, if you leave it like this, you will run into issues where the x and y values result in the ball only moving on a straight cross sectional line along the x-axis or vice versa along the y-axis when the value is too close to the max height or width of the canvas. To work around this issue, create a desired range for the values of your variables using:
Math.floor(Math.random() * (max - min) ) + min;
Example:
canvas.width = 800;
canvas.height = 600;
var x = Math.floor(Math.random() * (700 - 100)) + 100;
var y = Math.floor(Math.random() * (500-100)) + 100;

Related

Rotating Rectangles Around Circle Perimeter on Canvas

I'm trying to create a little circular "equalizer" effect using JavaScript and HTML canvas for a little project I'm working on, and it works great, except one little thing. It's just a series of rectangular bars moving in time to an mp3 - nothing overly fancy, but at the moment all the bars point in one direction (i.e. 0 radians, or 90 degrees).
I want each respective rectangle around the edge of the circle to point directly away from the center point, rather than to the right. I have 360 bars, so naturally, each one should be 1 degree more rotated than the previous.
I thought that doing angle = i*Math.PI/180 would fix that, but it doesn't seem to matter what I do with the rotate function - they always end up pointing in weird and wonderful directions, and being translated a million miles from where they were. And I can't see why. Can anyone see where I'm going wrong?
My frame code, for reference, is as follows:
function frames() {
// Clear the canvas and get the mp3 array
window.webkitRequestAnimationFrame(frames);
musicArray = new Uint8Array(analyser.frequencyBinCount);
analyser.getByteFrequencyData(musicArray);
ctx.clearRect(0, 0, canvas.width, canvas.height);
bars = 360;
for (var i = 0; i < bars; i++) {
// Find the rectangle's position on circle edge
distance = 100;
var angle = i * ((Math.PI * 2) / bars);
var x = Math.cos(angle) * distance + (canvas.width / 2);
var y = Math.sin(angle) * distance + (canvas.height / 2);
barWidth = 5;
barHeight = (musicArray[i] / 4);
// Fill with a blue-green gradient
var grd = ctx.createLinearGradient(x, 0, x + 40, 0);
grd.addColorStop(0, "#00CCFF");
grd.addColorStop(1, "#00FF7F");
ctx.fillStyle = grd;
// Rotate the rectangle according to position
// ctx.rotate(i*Math.PI/180); - DOESN'T WORK
// Draw the rectangle
ctx.fillRect(x, y, barHeight, barWidth);
}
For clarity I've removed part of your code. I'm using rotate as you intended. Also I'm using barHeight = (Math.random()* 50); instead your (musicArray[i]/4); because I wanted to have something to show.
Also I've changed your bars to 180. It's very probable that you won't have 360 bars but 32 or 64 or 128 or 256 . . . Now you can change the numbers of bare to one of these numbers to see the result.
I'm drawing everything around the origin of the canvas and translating the context in the center.
I hope it helps.
const canvas = document.getElementById("c");
const ctx = canvas.getContext("2d");
let cw = canvas.width = 400;
let ch = canvas.height = 400;
let bars = 180;
let r = 100;
ctx.translate(cw / 2, ch / 2)
for (var i = 0; i < 360; i += (360 / bars)) {
// Find the rectangle's position on circle edge
var angle = i * ((Math.PI * 2) / bars);
//var x = Math.cos(angle)*r+(canvas.width/2);
//var y = Math.sin(angle)*r+(canvas.height/2);
barWidth = 2 * Math.PI * r / bars;
barHeight = (Math.random() * 50);
ctx.fillStyle = "green";
// Rotate the rectangle according to position
// ctx.rotate(i*Math.PI/180); - DOESN'T WORK
// Draw the rectangle
ctx.save();
ctx.rotate(i * Math.PI / 180);
ctx.fillRect(r, -barWidth / 2, barHeight, barWidth);
//ctx.fillRect(r ,0, barHeight, barWidth);
ctx.restore();
}
canvas {
border: 1px solid
}
<canvas id="c"></canvas>
Here is another solution, I'm preserving your initial trigonometry approach.
But instead of rectangles I used lines, I don't think it makes a difference for you, if what you need is bars moving in time to an mp3 all you need to do is change the var v = Math.random() + 1; to a reading from the Amplitude, and those bars will be dancing.
const canvas = document.getElementById("c");
canvas.width = canvas.height = 170;
const ctx = canvas.getContext("2d");
ctx.translate(canvas.width / 2, canvas.height / 2)
ctx.lineWidth = 2;
let r = 40;
let bars = 180;
function draw() {
ctx.clearRect(-100, -100, 200, 200)
for (var i = 0; i < 360; i += (360 / bars)) {
var angle = i * ((Math.PI * 2) / bars);
var x = Math.cos(angle) * r;
var y = Math.sin(angle) * r;
ctx.beginPath();
var v = Math.random() + 1;
ctx.moveTo(x, y);
ctx.lineTo(x * v, y * v)
grd = ctx.createLinearGradient(x, y, x*2, y*2);
grd.addColorStop(0, "blue");
grd.addColorStop(1, "red");
ctx.strokeStyle = grd;
ctx.stroke();
}
}
setInterval(draw, 100)
<canvas id="c"></canvas>

Adding perspective to fake 3D animation

I'm working on a canvas-based animation, and I'm trying to get a 3D effect in a 2D canvas.
So far, things are going well! I've got my "orbiting line of triangles" working very well:
var c = document.createElement('canvas');
c.width = c.height = 100;
document.body.appendChild(c);
var ctx = c.getContext("2d");
function Triangles() {
this.rotation = {
x: Math.random()*Math.PI*2,
y: Math.random()*Math.PI*2,
z: Math.random()*Math.PI*2
};
/* Uncomment this for testing perspective...
this.rotation = {
x: Math.PI/2,
y: 0,
z: 0
};
*/
}
Triangles.prototype.draw = function(t) {
this.rotation.z += t/1000;
var i, points;
for( i=0; i<15; i++) {
points = [
this.computeRotation(Math.cos(0.25*i),-Math.sin(0.25*i),0),
this.computeRotation(Math.cos(0.25*(i+1)),-Math.sin(0.25*(i+1)),-0.1),
this.computeRotation(Math.cos(0.25*(i+1)),-Math.sin(0.25*(i+1)),0.1)
];
ctx.fillStyle = "black";
ctx.beginPath();
ctx.moveTo(50+40*points[0][0],50+40*points[0][1]);
ctx.lineTo(50+40*points[1][0],50+40*points[1][1]);
ctx.lineTo(50+40*points[2][0],50+40*points[2][1]);
ctx.closePath();
ctx.fill();
}
};
Triangles.prototype.computeRotation = function(x,y,z) {
var rz, ry, rx;
rz = [
Math.cos(this.rotation.z) * x - Math.sin(this.rotation.z) * y,
Math.sin(this.rotation.z) * x + Math.cos(this.rotation.z) * y,
z
];
ry = [
Math.cos(this.rotation.y) * rz[0] + Math.sin(this.rotation.y) * rz[2],
rz[1],
-Math.sin(this.rotation.y) * rz[0] + Math.cos(this.rotation.y) * rz[2]
];
rx = [
ry[0],
Math.cos(this.rotation.x) * ry[1] - Math.sin(this.rotation.x) * ry[2],
Math.sin(this.rotation.x) * ry[1] + Math.cos(this.rotation.x) * ry[2]
];
return rx;
};
var tri = new Triangles();
requestAnimationFrame(function(start) {
function step(t) {
var delta = t-start;
ctx.clearRect(0,0,100,100)
tri.draw(delta);
start = t;
requestAnimationFrame(step);
}
step(start);
});
As you can see it's using rotation matrices for calculating the position of the points after their rotation, and I'm using this to draw the triangles using the output x and y coordinates.
I want to take this a step further by using the z coordinate and adding perspective to this animation, which will make the triangles slightly bigger when in the foreground, and smaller when in the background. However, I'm not sure how to go about doing this.
I guess this is more of a maths question than a programming one, sorry about that!
Define a focal length to control the amount of perspective. The greater the value the less the amount of perspective. Then
var fl = 200; // focal length;
var px = 100; // point in 3D space
var py = 200;
var pz = 500;
Then to get the screen X,Y
var sx = (px * fl) / pz;
var sy = (py * fl) / pz;
The resulting point is relative to the center of the veiw so you need to center it to the canvas.
sx += canvas.width/2;
sy += canvas.height/2;
That is a point.
It assumes that the point being viewed is in front of the view and further than the focal length from the focal point.
I've managed to figure out a basic solution, but I'm sure there's better ones, so if you have a more complete answer feel free to add it! But for now...
Since the coordinate system is already based around the origin with the viewpoint directly on the Z axis looking at the (x,y) plane, it's actually sufficient to just multiply the (x,y) coordinates by a value proportional to z. For example, x * (z+2)/2 will do just fine in this case
There's bound to be a more proper, general solution though!

Construct a circle of nested squares

I want to construct a circle of nested squares like this:
In the moment, I am programming in JavaScript/HTML5 canvas. This is my code:
<html>
<head>
<title>Circle of squares</title>
<script type="text/javascript">
var r = 150, u = 20, nests = 200; //radius in pixels, circumference in squares, nests in squares
var w = r; //any number != 0
function getNewW()
{
if(u < 3)
alert("Error: u < 3 (" + u + " < 3)!");
var tangents = new Array(new Array(0, w/2), new Array(Math.sin((1/u*360)*(Math.PI/180))*(w/2), -Math.cos((1/u*360)*(Math.PI/180))*(w/2)));
var sta = new Array(new Array(r, 0), new Array(Math.cos((1/u*360)*(Math.PI/180))*r, Math.sin((1/u*360)*(Math.PI/180))*r));
var end = new Array(new Array(sta[0][0]+tangents[0][0], sta[0][1]+tangents[0][1]), new Array(sta[1][0]+tangents[1][0], sta[1][1]+tangents[1][1]));
var pts = new Array(sta[0], end[0], sta[1], end[1]);
var intersect = new Array(((pts[0][0]*pts[1][1]-pts[0][1]*pts[1][0])*(pts[2][0]-pts[3][0]) - (pts[0][0]-pts[1][0])*(pts[2][0]*pts[3][1]-pts[2][1]*pts[3][0])) / ((pts[0][0]-pts[1][0])*(pts[2][1]-pts[3][1]) - (pts[0][1]-pts[1][1])*(pts[2][0]-pts[3][0])), ((pts[0][0]*pts[1][1]-pts[0][1]*pts[1][0])*(pts[2][1]-pts[3][1]) - (pts[0][1]-pts[1][1])*(pts[2][0]*pts[3][1]-pts[2][1]*pts[3][0])) / ((pts[0][0]-pts[1][0])*(pts[2][1]-pts[3][1]) - (pts[0][1]-pts[1][1])*(pts[2][0]-pts[3][0]))); //Formula from http://en.wikipedia.org/wiki/Line%E2%80%93line_intersection
//distTo0 should be equal to distTo1
var distTo0 = Math.sqrt(Math.pow(sta[0][0]-intersect[0], 2) + Math.pow(sta[0][1]-intersect[1], 2));
var distTo1 = Math.sqrt(Math.pow(sta[1][0]-intersect[0], 2) + Math.pow(sta[1][1]-intersect[1], 2));
if(Math.round(distTo0*100)/100 != Math.round(distTo1*100)/100)
alert("Error: distTo0 != distTo1 (" + distTo0 + " != " + distTo1 + ")!");
return distTo0*2;
}
function start()
{
var canvas = document.getElementById("outputCanvas");
canvas.setAttribute("width", 600);
canvas.setAttribute("height", 600);
if(canvas.getContext)
{
var ctx = canvas.getContext("2d");
ctx.translate(300, 300);
w = getNewW();
for(var i=0; i<u; i++)
{
ctx.rotate((1/u*360)*(Math.PI/180));
ctx.fillRect(r, -w/2, w, w);
}
for(var j=1; j<nests; j++)
{
var oldr = r;
var temp1 = 1/(10*j+1);
while(r+w > oldr) //This is the while-loop that makes the program slow
{
r -= temp1;
w = getNewW();
}
if(r < 0) //When the radius gets smaller than 0, the center is reached -> no new squares have to be drawn
break;
var temp2 = (1/u*360)*(Math.PI/180);
for(var i=0; i<u; i++)
{
ctx.rotate(temp2);
ctx.fillRect(r, -w/2, w, w);
}
}
}
}
</script>
</head>
<body id="main" onload="start()">
<canvas style="border:1px #000000 solid;" width="0" height="0" id="outputCanvas">Canvas not supported...</canvas>
<div id="info"> </div>
</body>
</html>
But because I don't have a formula for the solution, I use a while-loop to get closer and closer to the solution (until it has reached zero because of float-inaccuracy), that's why it's quite slow.
So, what formula can be used to calculate the width of the next square inside the (thought) circle and, if necessary, how could the code be optimized elsewhere?
Near the center of the circle, where the squares are small enough, you can approximate the length of the side (w) by the arc length - that is, how long one uth of the inner circle would be if you drew it as an actual circle. That's just the angle in radians (2 π/u) times the radius of the circle that goes through the inner corners of the square. Since you have r varying in your code, I'll call the specific radius value under consideration at a single moment r2; that makes the arc length this:
w_approx = (2 * Math.PI / u) * r2
But for most of the squares in your picture, the difference between that and the actual value of w is too great; if you use that as the side length, you'll get overlapping squares. Fortunately, we can calculate the true value of w directly, too; it just requires a little trigonometry.
If you draw lines from the inner corners of the square to the center of the circle, those two lines plus the inner side of the square form a triangle. We know how long those two lines we just drew are; they're equal to the inner radius. We don't know how long the third side is - that's the value of w we're looking for - but we do know the angle opposite it. Those three pieces of information are enough to calculate w.
Here's a picture to show what I'm talking about:
The angle at the center of the circle, labeled α (alpha) in the picture, is just one uth of a full circle, which is 2 π /u radians (or 360/u degrees, but the trig functions all expect radians):
alpha = 2 * Math.PI / u
The other two angles of the triangle are equal (they have to be, because they're opposite sides that are of equal length), so they're both labeled β. Since the three angles of a triangle always add up to π radians (or 180º), we can calculate β; it's equal to (π - α)/2 radians:
beta = (Math.PI - alpha)/2
By the Law of Sines, if you divide the length of any side of any triangle by the sine of the angle opposite that side, the result is the same no matter which of the three sides you picked. That tells us that w/sin α must be the same as r2/sin β. Solving that equation for w gets us this:
w = r2 * Math.sin(alpha) / Math.sin(beta)
Solution is quite easy :
What are the parameters ?
• The start radius of your circle.
• The end radius of your circle.
• The number of square per circle.
Then what do you need to compute ?
• The rotation to be performed between two circles : easy ,that's just a full rotation divided by the number of square per circle :
var angle = 2 * Math.PI / squaresPerCircle;
• The size of each square, given the current radius. Easy also : compute the circumference of the current circle (2*PI*radius), then the size of one square is approximately this circumference divided by the number of squares (since you want to fill the circle) :
squareSize = 2 * Math.PI * currentRadius / squaresPerCircle;
approximation is good enough even for like 10 squares per circles.
(
Otherwise the 'real' way to get the height when you have radius and angle is done with :
squareSize = 2 * currentRadius * Math.tan(angle/2);
)
Snippet :
// parameters
var startRadius = 5;
var maxRadius = 200;
var squaresPerCircle = 20;
function start() {
// boilerplate
var canvas = document.getElementById("outputCanvas");
var ctx = canvas.getContext("2d");
canvas.width = 600;
canvas.height = 600;
//
ctx.save();
ctx.translate(canvas.width / 2, canvas.height / 2);
var currentRadius = startRadius;
var angle = 2 * Math.PI / squaresPerCircle;
// loop on each ring
do {
squareSize = 2 * Math.PI * currentRadius / squaresPerCircle;
// squareSize = 2 * currentRadius * Math.tan(angle/2);
ctx.save();
// loop on every square of a single ring
for (var cIndex = 0; cIndex < squaresPerCircle; cIndex++) {
ctx.fillRect(currentRadius, -squareSize / 2,
squareSize, squareSize);
ctx.rotate(angle);
};
ctx.restore();
currentRadius += squareSize;
} while (currentRadius < maxRadius);
ctx.restore();
}
onload = start;
<canvas style="border:1px #000000 solid;" width="0" height="0" id="outputCanvas">Canvas not supported...</canvas>

Calculating evenly spaced points on the perimeter of a circle

The math behind this question has been asked numerous times, so that's not specifically what I'm after. Rather, I'm trying to program the equation for determining these points into a loop in JavaScript, so that I can display points the evenly around the circle.
So with the equations for the X and Y positions of the points:
pointX = r * cos(theta) + centerX
pointY = r * sin(theta) + centerY
I should be able to calculate it with this:
var centerX = 300;
var centerY = 175;
var radius = 100;
var numberOfPoints = 8;
var theta = 360/numberOfPoints;
for ( var i = 1; i <= numberOfPoints; i++ ) {
pointX = ( radius * Math.cos(theta * i) + centerX );
pointY = ( radius * Math.sin(theta * i) + centerY );
// Draw point ( pointX , pointY )
}
And it should give me the x,y coordinates along the perimeter for 8 points, spread 45° from each other. But this doesn't work, and I'm not understanding why.
This is the output that I get (using the HTML5 Canvas element). The points should reside on the innermost red circle, as that one has a
Incorrect:
When it "should" look like this (although this is with just 1 point, placed manually):
Correct:
Could someone help me out? It's been years since I took trig, but even with looking at other examples (from various languages), I don't see why this isn't working.
Update: Figured it out!
I didn't need to add the centerX and centerY to each calculation, because in my code, those points were already relative to the center of the circle. So, while the canvas center was at point (300, 175), all points were relative to the circle that I created (the stroke line that they need to be placed on), and so the center for them was at (0, 0). I removed this from the code, and split the theta and angle calculations into two variables for better readability, and voila!
totalPoints = 8;
for (var i = 1; i <= totalPoints ; i++) {
drawPoint(100, i, totalPoints);
}
function drawPoint(r, currentPoint, totalPoints) {
var theta = ((Math.PI*2) / totalPoints);
var angle = (theta * currentPoint);
electron.pivot.x = (r * Math.cos(angle));
electron.pivot.y = (r * Math.sin(angle));
return electron;
}
Correct:
cos and sin in Javascript accept an argument in radians, not degrees. You can change your theta calculation to
var theta = (Math.PI*2)/numberOfPoints;
See the Math.cos documentation for details
#Emmett J. Butler's solution should work. The following is a complete working example
// canvas and mousedown related variables
var canvas = document.getElementById("canvas");
var ctx = canvas.getContext("2d");
var $canvas = $("#canvas");
var canvasOffset = $canvas.offset();
var offsetX = canvasOffset.left;
var offsetY = canvasOffset.top;
var scrollX = $canvas.scrollLeft();
var scrollY = $canvas.scrollTop();
// save canvas size to vars b/ they're used often
var canvasWidth = canvas.width;
var canvasHeight = canvas.height;
var centerX = 150;
var centerY = 175;
var radius = 100;
var numberOfPoints = 8;
var theta = 2.0*Math.PI/numberOfPoints;
ctx.beginPath();
for ( var i = 1; i <= numberOfPoints; i++ ) {
pointX = ( radius * Math.cos(theta * i) + centerX );
pointY = ( radius * Math.sin(theta * i) + centerY );
ctx.fillStyle = "Red";
ctx.fillRect(pointX-5,pointY-5,10,10);
ctx.fillStyle = "Green";
}
ctx.stroke();

Keeping shape and animation of ball consistance over period of time

I am new to two.js. I am trying some basic experiments with rubber ball example to reposition ball on every second as per random input instead of mouse movement.
So, I have written below code, but it is removing rubber ball effect after some iteration. I don't know what is going wrong.
Second problem, after some iteration, rubber ball is changing its shape from circle to oval kind of shape.
JSFiddle: http://jsfiddle.net/2v93n/ Tried many times, but not working live with jsFiddle.
<body>
<script>
var two = new Two({
fullscreen: true,
autostart: true
}).appendTo(document.body);
Two.Resoultion = 32;
var delta = new Two.Vector();
var mouse = new Two.Vector();
var drag = 0.1;
var radius = 25;
var shadow = two.makeCircle(two.width / 2, two.height / 2, radius);
var ball = two.makeCircle(two.width / 2, two.height / 2, radius);
ball.noStroke().fill = 'green';shadow.noStroke().fill = 'rgba(0, 0, 0, 0.2)'; shadow.scale = 0.85;
function moveRubberBall() {
shadow.offset = new Two.Vector(- radius / 2, radius * 2);
_.each(ball.vertices, function(v) {
v.origin = new Two.Vector().copy(v);
});
mouse.x = Math.floor((Math.random() * 1000) + 1);
mouse.y = Math.floor((Math.random() * 600) + 1);
shadow.offset.x = 5 * radius * (mouse.x - two.width / 2) / two.width;
shadow.offset.y = 5 * radius * (mouse.y - two.height / 2) / two.height;
two.bind('update', function() {
delta.copy(mouse).subSelf(ball.translation);
_.each(ball.vertices, function(v, i) {
var dist = v.origin.distanceTo(delta);
var pct = dist / radius;
var x = delta.x * pct;
var y = delta.y * pct;
var destx = v.origin.x - x;
var desty = v.origin.y - y;
v.x += (destx - v.x) * drag;
v.y += (desty - v.y) * drag;
shadow.vertices[i].copy(v);
});
ball.translation.addSelf(delta);
shadow.translation.copy(ball.translation);
shadow.translation.addSelf(shadow.offset);
});
}
var auto_refresh = setInterval("moveRubberBall()", 1000);
</script>
</body>
Please help somebody.
The main issue is that two.bind('update'...) is within moveRubberBall(). When you bind to update it means this function will be called on requestAnimationFrame, effectively 60FPS. When the event is bound every time moveRubberBall is called — once a second — it adds another callback. So after 5 seconds there will be 5 updates called 60FPS. I updated your fiddle to import two.js correctly and fix this error outlined:
http://jsfiddle.net/2v93n/1/

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