We Keep Coding

Natural Movement with Noise

Im creating an object that randomly moves in a natural way using noise like this (works as intended):
The objects encounter a collision and their trajectory is manipulated, the movement path now changes to straight line (words as intended)
thisRabbit.x = _world.width * (noise(thisRabbit.t));
thisRabbit.y = _world.height * (noise(thisRabbit.t+5));
thisRabbit.t += 0.001;
The problem is after this movement , i want the object to start moving in a random direction again as it was initially. If i use the same function, the object jumps to the last location before the trajectory was modified.
let vx = this.acquiredFood[0] - this.x;
let vy = this.acquiredFood[1] - this.y;
let f = (this.genes.speed + 10) / Math.sqrt(vx*vx+vy*vy);
vx = vx * f;
vy = vy * f;
let newX = this.x + vx;
let newY = this.y + vy;
So how do i get the object to move as before, given a starting position
edit: snippet here: https://editor.p5js.org/vince.chinner/sketches/HPFKR8eIw

Your problem is that you used a factor from 0 to 1 generated with noise and an incremented seed to generate the position by multiplying directly the world dimentions. When reaching food, you cannot increment the seed as to be in the exact position where the movement to get your food led you (I found no inverse function for noise to get the seed from the return value).
What you need to do instead is use the noise to increment or decrement the coordinates, so that no matter where the seed is, you don't loose your current position.
Here are the different corrections I applied to the code, as there were also syntax errors, I can't really paste the whole stuff here for copyright reasons (you didn't share the whole code here and the sketch belongs to you)
MAIN CORRECTION:
used a var found because returning from the forEach callback doesn't make you leave the findFood function, but the callback one. And the forEach loop doesn't stop. Using this var prevents the further forEach tests to be made and allows you to return from findFood so that no further move is made after seeing food.
noise is now applied to a value of 4 and I subtract 2, so that x and y now change with a range of -2 to 2 each. Of course, with this method, you need to check against world dimentions or else the rabbit could leave the world. The seed increment has been changed too or else it would vary too slowly (adapt values as you wish)
findFood(){
var thisRabbit = this, found = false;
_world.food.forEach(f => {
if(!found){
let d = int(dist(f[0], f[1], thisRabbit.x, thisRabbit.y));
if(d < (thisRabbit.genes.vision / 2)+3){
thisRabbit.state = "foundFood";
this.acquiredFood = f;
found = true;
}
}
});
if(found){ return; }
thisRabbit.x += (noise(thisRabbit.t) * 4) - 2;
if(thisRabbit.x < 0){ thisRabbit.x = 0; }
if(thisRabbit.x > _world.width){ thisRabbit.x = _world.width; }
thisRabbit.y += (noise(thisRabbit.t + 5) * 4) - 2;
if(thisRabbit.y < 0){ thisRabbit.y = 0; }
if(thisRabbit.y > _world.height){ thisRabbit.y = _world.height; }
thisRabbit.t += 0.01;
}
SYNTAX ERRORS:
lines 23 / 24: assignment should be with a value (null or false)
this.genes = null;
this.acquiredFood = null;
lines 129 to 133: end you instructions with a ; instead of a ,
this.width = w;
this.height = h;
this.foodDensity = foodDensity;
this.food = [];
this.rabits = [];
line 156 to 160: there should be no space between rabbit and .t. Additionnally, because the coordinates are not directly linked to t, I would prefer to use random for starting position:
let x = this.width * random();
let y = this.height * random();
let _rabbit = new rabbit(x, y);
_rabbit.genes = genes;
_rabbit.t = t;

Canvas animation with JavaScript. Random coordinates and speed at every initiation

Edited : Thanks to all for valuable time and effort. Finally I made this )) JSfiddle
I was just playing with canvas and made this. Fiddle link here.
... some code here ...
var cords = [];
for(var i = 50; i <= width; i += 100) {
for(var j = 50; j <= height; j += 100) {
cords.push({ cor: i+','+j});
}
}
console.log(cords);
var offset = 15,
speed = 0.01,
angle = 0.01;
cords.forEach(function(e1) {
e1.base = parseInt(Math.random()*25);
e1.rgb = 'rgb('+parseInt(Math.random()*255)+','+parseInt(Math.random()*255)+','+parseInt(Math.random()*255)+')';
});
setInterval(function() {
cords.forEach(function(e1) {
e1.base = parseInt(Math.random()*25);
e1.rgb = 'rgb('+parseInt(Math.random()*255)+','+parseInt(Math.random()*255)+','+parseInt(Math.random()*255)+')';
});
},5000);
function render() {
ctx.clearRect(0,0,width,height);
cords.forEach(function(e1) {
//console.log(e1);
ctx.fillStyle = e1.rgb;
ctx.beginPath();
var r = e1.base + Math.abs(Math.sin(angle)) * offset;
var v = e1.cor.split(',');
ctx.arc(v[0],v[1],r,0,Math.PI * 2, false);
ctx.fill();
});
angle += speed;
requestAnimationFrame(render);
}
render();
Was wondering if -
Coordinates can be made random, now they are fixed as you can see. After 5000 mil, balls will show up in various random cords but even at their fullest they won't touch each other.
Every ball has same speed for changing size, I want that to be different too. Meaning, After 5000 mil, they show up with different animation speeds as well.
Also any suggestion on improving code and making it better/quicker/lighter is much appreciated. Thank you !

TL;DR - See it running here.
Making the coordinates random:
This requires you to add some random displacement to the x and y coordinates. So I added a random value to the coordinates. But then a displacement of less than 1 is not noticeable. So you'd need to magnify that random number by a multiplier. That's where the randomizationFactor comes in. I have set it to 100 since that is the value by which you shift the coordinates in each iteration. So that gives a truly random look to the animation.
Making Speed Random:
This one took me a while to figure out, but the ideal way is to push a value of speed into the array of coordinates. This let's you ensure that for the duration of animation, the speed will remain constant and that gives you a smoother feel. But again multiplying the radius r with a value between 0 and 1 reduces the speed significantly for some of the circles. So I have added a multiplier to 3 to compensate slightly for that.
Ideally I'd put a 2, as the average value of Math.random() is 0.5, so a multiplier of 2 would be adequate to compensate for that. But a little experimentation showed that the multiplier of 3 was much better. You can choose the value as per your preference.
Your logic of generating the coordinates changes as follows:
for(var i = 50; i <= width;i += 100) {
for(var j = 51; j <= height;j += 100) {
var x = i + (Math.random() - 0.5)*randomizationFactor;
var y = j + (Math.random() - 0.5)*randomizationFactor;
cords.push({ cor: x+','+y, speed: Math.random()});
}
}
Your logic of enlarging the circles changes as follows:
function render() {
ctx.clearRect(0,0,width,height);
cords.forEach(function(e1) {
//console.log(e1);
ctx.fillStyle = e1.rgb;
ctx.beginPath();
var r = e1.base + Math.abs(Math.sin(angle)) * offset * e1.speed * 3;
var v = e1.cor.split(',');
ctx.arc(v[0],v[1],r,0,Math.PI * 2, false);
ctx.fill();
});
angle += speed ;
requestAnimationFrame(render);
}
Suggestion: Update the coordinates with color
I'd probably also update the location of circles every 5 seconds along with the colors. It's pretty simple to do as well. Here I've just created a function resetCoordinates that runs every 5 seconds along with the setBaseRgb function.
var cords = [];
function resetCoordinates() {
cords = [];
for(var i = 50; i <= width;i += 100) {
for(var j = 51; j <= height;j += 100) {
var x = i + (Math.random() - 0.5)*randomizationFactor;
var y = j + (Math.random() - 0.5)*randomizationFactor;
cords.push({ cor: x+','+y, speed: Math.random()});
}
}
}

UPDATE I did some fixes in your code that can make your animation more dynamic. Totally rewritten sample.
(sorry for variable name changing, imo now better)
Built in Math.random not really random, and becomes obvious when you meet animations. Try to use this random-js lib.
var randEngine = Random.engines.mt19937().autoSeed();
var rand = function(from, to){
return Random.integer(from, to)(randEngine)
}
Internal base properties to each circle would be better(more dynamic).
var circles = [];
// better to save coords as object neither as string
for(var i = 50; i <= width; i += 100)
for(var j = 50; j <= height; j += 100)
circles.push({
coords: {x:i,y:j}
});
We can adjust animation with new bouncing property.
var offset = 15,
speed = 0.005,
angle = 0.01,
bouncing = 25;
This is how setBaseRgb function may look like
function setBaseRgb(el){
el.base = rand(-bouncing, bouncing);
el.speed = rand(5, 10) * speed;
el.angle = 0;
el.rgb = 'rgb('+rand(0, 255)+','+rand(0, 255)+','+rand(0, 255)+')';
}
All your animations had fixed setInterval timeout. Better with random timeout.
cords.forEach(function(el){
// random timeout for each circle
setInterval(setBaseRgb.bind(null,el), rand(3000, 5000));
})
You forgot to add your base to your circle position
function render() {
ctx.clearRect(0,0,width,height);
circles.forEach(function(el) {
ctx.fillStyle = el.rgb;
ctx.beginPath();
var r = bouncing + el.base + Math.abs(Math.sin(el.angle)) * offset;
var coords = el.coords;
ctx.arc(
coords.x + el.base,
coords.y + el.base,
r, 0, Math.PI * 2, false
);
ctx.fill();
el.angle += el.speed;
});
requestAnimationFrame(render);
}
render();
Effect 1 JSFiddle
Adding this
if(el.angle > 1)
el.angle=0;
Results bubling effect
Effect 2 JSFiddle
Playing with formulas results this
Effect 3 JSFiddle

algorithm to randomly & efficiently place 100 circles without any overlap?

I am trying to write a script to place 100 circles of varying sizes onto a stage. I've outlined the concise requirements below.
Given the following:
var stage; // contains a "width" and "height" property.
var circle; // the circle class. contains x, y, radius & a unique id property.
var circleArray; // contains 100 circle instances
requirements:
write a function to place 100 circles of varying radius onto the stage.
placements must be random but evenly distributed (no clumping).
placement must be performant - this will be executing on a mobile web browser.
circles must not intersect/overlap other circles.
circle.x >= 0 must be true.
circle.y >= 0 && circle.y <= stage.height must be true.
circles may have any of the following radius sizes (assigned at creation):
150
120
90
80
65
My current attempt is a brute-force method, which does not operate efficiently. If I attempt to insert any more than ~10 circles, the browser hangs. Below is my current implementation, which I am completely OK with throwing away in favor of a more performant / better one.
Here is a live demo (NOTE: there is no actual drawing code, just the logic, but it will still lock up the browser so be warned!!) http://jsbin.com/muhiziduxu/2/edit?js,console
function adjustForOverlap (circleArray) {
// a reference to the circle that is invoking this function.
var _this = this;
// remove this circle from the array we are iterating over.
var arr = circleArray.filter(function (circle){
return circle.id !== _this.id;
});
// while repeat == true, the circle may be overlapping something.
var repeat = true;
while(repeat) {
var hasOverlap = false;
for (var i=0; i<arr.length; i++) {
var other = arr[i];
var dx = _self.x - other.x;
var dy = _self.y - other.y;
var rr = _self.radius + other.radius;
if (dx * dx + dy * dy < rr * rr) {
// if here, then an overlap was detected.
hit = true;
break;
}
}
// if hit is false, the circle didn't overlap anything, so break.
if (hit === false) {
repeat = false;
break;
} else {
// an overlap was detected, so randomize position.
_self.x = Math.random() * (stage.width*2);
_self.y = Math.random() * stage.height;
}
}
}

There are lots of efficient collision detection algorithms. Many of them work by dividing up the space into cells and maintaining a separate data structure with efficient lookup of other objects in the cell. The basic steps are:
Identify a random spot for your new circle
Determine which cells it's in
Look in each of those cells for a collision
If there's a collision, goto 1.
Else, add the new circle to each of the cells it overlaps.
You can use a simple square grid (i.e. a 2-d array) for the cell data structure, or something else like a quadtree. You can also in some cases get a bit of extra speed by trying a cheap-but-coarse collision check first (do the bounding boxes overlap), and if that returns true try the slightly more expensive and exact check.
Update
For quadtrees, check out d3-quadtree, which ought to give you a pretty good implementation, with examples.
For a (very quick, untested) 2-d array implementation:
function Grid(radius, width, height) {
// I'm not sure offhand how to find the optimum grid size.
// Let's use a radius as a starting point
this.gridX = Math.ceil(width / radius);
this.gridY = Math.ceil(height / radius);
// Determine cell size
this.cellWidth = width / this.gridX;
this.cellHeight = height / this.gridY;
// Create the grid structure
this.grid = [];
for (var i = 0; i < gridY; i++) {
// grid row
this.grid[i] = [];
for (var j = 0; j < gridX; j++) {
// Grid cell, holds refs to all circles
this.grid[i][j] = [];
}
}
}
Grid.prototype = {
// Return all cells the circle intersects. Each cell is an array
getCells: function(circle) {
var cells = [];
var grid = this.grid;
// For simplicity, just intersect the bounding boxes
var gridX1Index = Math.floor(
(circle.x - circle.radius) / this.cellWidth
);
var gridX2Index = Math.ceil(
(circle.x + circle.radius) / this.cellWidth
);
var gridY1Index = Math.floor(
(circle.y - circle.radius) / this.cellHeight
);
var gridY2Index = Math.ceil(
(circle.y + circle.radius) / this.cellHeight
);
for (var i = gridY1Index; i < gridY2Index; i++) {
for (var j = gridX1Index; j < gridX2Index; j++) {
// Add cell to list
cells.push(grid[i][j]);
}
}
return cells;
},
add: function(circle) {
this.getCells(circle).forEach(function(cell) {
cell.push(circle);
});
},
hasCollisions: function(circle) {
return this.getCells(circle).some(function(cell) {
return cell.some(function(other) {
return this.collides(circle, other);
}, this);
}, this);
},
collides: function (circle, other) {
if (circle === other) {
return false;
}
var dx = circle.x - other.x;
var dy = circle.y - other.y;
var rr = circle.radius + other.radius;
return (dx * dx + dy * dy < rr * rr);
}
};
var g = new Grid(150, 1000, 800);
g.add({x: 100, y: 100, radius: 50});
g.hasCollisions({x: 100, y:80, radius: 100});
Here's a fully-functional example: http://jsbin.com/cojoxoxufu/1/edit?js,output
Note that this only shows 30 circles. It looks like the problem is often unsolvable with your current radii, width, and height. This is set up to look for up to 500 locations for each circle before giving up and accepting a collision.

Fast 3D matrix re-slicing

I have a 3D matrix of size (X, Y, Z) which is stored in a data structure as Z matrices, each X x Y in size. I would like to re-slice these matrices to obtain X slices, each Y x Z in size. In other words, I want to reslice a 3D matrix stored as XY slices in the YZ plane. The use case is to reslice axial CT images into sagittal images. I am working inside a browser environment.
Here's an example of what I am trying to achieve:
I have implemented the naive (iterative) solution in Python, which takes O(Y * Z) per slice. I haven't even bothered writing out the corresponding JavaScript implementation, because this approach is too slow by several orders of magnitude.
import glob
import numpy as np
import matplotlib.pyplot as plt
from scipy.misc import imread
height, width, depth = 512, 512, 100
volume = np.zeros((height, width, depth))
s = 0
for filename in glob.iglob('./*.jpg'):
volume[:,:,s] = imread(filename)[...,0]/255.0
s += 1
reslice = np.zeros((depth, height, width))
for s in xrange(0, width):
current = np.zeros((depth, height))
for i in xrange(0, height):
for j in xrange(0, depth):
current[j,i] = volume[i,s,j]
reslice[:,:,s] = current
This algorithm seems to be amenable to parallelization. For example, in CUDA, one could load the 3D data into global memory, create one thread per pixel, then iterate for every slice in the new direction, and on each iteration ask the right pixels to fire in order to fill out the current slice. This would be a trivial kernel to write, and would be approximately O(1) per slice. However, I don't have access to CUDA in the browser.
Mapping from CUDA to WebCL is relatively straightforward, but WebCL is out of question given inexistent vendor support ATM. Therefore, I'm thinking WebGL is the ideal solution.
I'm not too sure how this would be done in the "WebGL" paradigm, but I'm sure it can be done, and I suspect it is fairly trivial as well. I can't seem to find where to start, however, and resources on doing general-purpose computations with OpenGL are extremely scarce. How would I go about using OpenGL to speed up reslicing of a 3D matrix inside the browser?

You don't have necessarily to use webGL to be fast enough.
If you use a 3D array, JavaScript might be too slow but by using a flat array the time to reslice is in fact similar to the time it takes to create the array!
Another trick is to use a typed array to reduce memory usage and improve performances (Uint8Array).
I created a small class to handle such a flat array and to slice it.
I think the most relevant thing you want is in fact to get a view, either on (x, y) axes or (y, z) axes.
Since Array creation is very slow, you want to build the view on place within a fixed buffer. And since you want also a sliced view, you have to create a buffer and method also for the sliced view.
It's fast: creating a view for your 512X512x100 example take less than 5 ms!
(So in fact, the putImageData you'll have to do afterward will quite take more time! )
Fiddle is here: http://jsfiddle.net/n38mwh95/1/
Here's the class handling the data, you'll have to change the constructor so it accepts the real raw data:
function Array3D(xSize, ySize, zSize) {
this.xSize = xSize;
this.ySize = ySize;
this.zSize = zSize;
var xyMultiplier = xSize * ySize;
this.array = new Uint8Array(xSize * ySize * zSize);
this.view = new Uint8Array(xSize * ySize);
this.slicedView = new Uint8Array(ySize * zSize);
this.valueAt = function (x, y, z) {
return this.array[x + xSize * (y + z * ySize)];
};
this.setValueAt = function (x, y, z, val) {
return this.array[x + xSize * (y + z * ySize)] = val;
};
this.buildView = function (z) {
var src = this.array;
var view = this.view;
for (var x = 0; x < xSize; x++) {
for (var y = 0; y < ySize; y++) {
view[x + xSize * y] = src[x + xSize * (y + z * ySize)];
}
}
return view;
};
this.buildSlicedView = function (x) {
var src = this.array;
var sView = this.slicedView;
for (var y = 0; y < ySize; y++) {
for (var z = 0; z < zSize; z++) {
sView[y + ySize * z] = src[x + xSize * (y + z * ySize)];
}
}
return sView;
};
}
In use:
var xSize = 512;
var ySize = 512;
var zSize = 100;
var t1, t2;
t1 = performance.now();
var testArray = new Array3D(xSize, ySize, zSize);
t2 = performance.now();
console.log('created in :' + (t2 - t1));
t1 = performance.now();
var resliced = testArray.buildView(10);
t2 = performance.now();
console.log('building view in :' + (t2 - t1));
var x = 80;
t1 = performance.now();
var resliced = testArray.buildSlicedView(x);
t2 = performance.now();
console.log('building sliced view in :' + (t2 - t1));
Results:
created in :33.92199998779688 (index):73
building view in :2.7559999871300533 (index):79
building sliced view in :5.726000003051013
At the end of the code I also added some code to render the view.
Don't forget to cache the canvas imageData: create it only once then re-use it for best performance.
You could easily have a real-time rendering in fact.

JS canvas implementation of Julia set

The problem is currently solved. In case some one wants to see the colored fractal, the code is here.
Here is the previous problem:
Nonetheless the algorithm is straight forward, I seems to have a small error (some fractals are drawing correctly and some are not). You can quickly check it in jsFiddle that c = -1, 1/4 the fractal is drawing correctly but if I will take c = i; the image is totally wrong.
Here is implementation.
HTML
<canvas id="a" width="400" height="400"></canvas>
JS
function point(pos, canvas){
canvas.fillRect(pos[0], pos[1], 1, 1); // there is no drawpoint in JS, so I simulate it
}
function conversion(x, y, width, R){ // transformation from canvas coordinates to XY plane
var m = R / width;
var x1 = m * (2 * x - width);
var y2 = m * (width - 2 * y);
return [x1, y2];
}
function f(z, c){ // calculate the value of the function with complex arguments.
return [z[0]*z[0] - z[1] * z[1] + c[0], 2 * z[0] * z[1] + c[1]];
}
function abs(z){ // absolute value of a complex number
return Math.sqrt(z[0]*z[0] + z[1]*z[1]);
}
function init(){
var length = 400,
width = 400,
c = [-1, 0], // all complex number are in the form of [x, y] which means x + i*y
maxIterate = 100,
R = (1 + Math.sqrt(1+4*abs(c))) / 2,
z;
var canvas = document.getElementById('a').getContext("2d");
var flag;
for (var x = 0; x < width; x++){
for (var y = 0; y < length; y++){ // for every point in the canvas plane
flag = true;
z = conversion(x, y, width, R); // convert it to XY plane
for (var i = 0; i < maxIterate; i++){ // I know I can change it to while and remove this flag.
z = f(z, c);
if (abs(z) > R){ // if during every one of the iterations we have value bigger then R, do not draw this point.
flag = false;
break;
}
}
// if the
if (flag) point([x, y], canvas);
}
}
}
Also it took me few minutes to write it, I spent much more time trying to find why does not it work for all the cases. Any idea where I screwed up?

Good news! (or bad news)
You're implementation is completely. correct. Unfortunately, with c = [0, 1], the Julia set has very few points. I believe it is measure zero (unlike say, the Mandelbrot set). So the probability of a random point being in that Julia set is 0.
If you reduce your iterations to 15 (JSFiddle), you can see the fractal. One hundred iterations is more "accurate", but as the number of iterations increase, the chance that a point on your 400 x 400 grid will be included in your fractal approximation decreases to zero.
Often, you will see the Julia fractal will multiple colors, where the color indicates how quickly it diverges (or does not diverge at all), like in this Flash demonstration. This allows the Julia fractal to be somewhat visible even in cases like c = i.
Your choices are
(1) Reduce your # of iterations, possibly depending on c.
(2) Increase the size of your sampling (and your canvas), possibly depending on c.
(3) Color the points of your canvas according to the iteration # at which R was exceeded.
The last option will give you the most robust result.