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clipping displacement in canvas javascript

I'm trying to create a two-dimensional board game with canvas for practice.
The goal is to have a game with only html, javascript and php.
I made a first canvas which takes up the entire board.
Currently my second canvas, contains a round pawn which moves as well as a clipping done with the clip () method.
My problem concerns the second canvas. I would like to be able to ensure that my clipping follows the position of the pawn.
But I can't move the clipping so it stays in the same place causing my pawn to appear and then disappear.
Could you tell me how to move this clipping please?
Thank you in advance.
const goUp = 1;
const goDown = 2;
const goLeft = 3;
const goRight = 4;
var canvas = document.getElementById("pawn");
var ctx = canvas.getContext("2d");
var largeurProprietee = 60;
var hauteurProprietee = 90;
x = 45 + 90 + (8 * 60) + 90;
y = 30;
orientation = 1;
pawnHeight = 40;
pawnWidth = 40;
function drawPawn() {
var image = new Image();
image.src = 'img/' + 'zelda' + '/' + 'vert' + '.png'; //adresse de l'image
image.onload = function() {
ctx.drawImage(this, y, x, pawnHeight, pawnWidth);
}
}
function shifting() {
erasePrevious();
cutOut();
drawPawn();
x--;
}
function erasePrevious() {
var previousX;
var previousY;
if (orientation == 1) {
previousX = x;
previousY = y;
ctx.clearRect(previousY, previousX, pawnHeight, pawnWidth);
}
}
function cutOut() {
var rayon = (pawnHeight / 2);
var clipX = (x + rayon);
var clipY = (y + rayon);
ctx.beginPath();
ctx.arc(clipY, clipX, rayon, 0, Math.PI * 2);
ctx.clip();
}
setInterval(shifting, 10);

Draw text pixel by pixel on canvas

I have a canvas where I use "fillText" with a string, saying for example "stackoverflow". Then I read the imagedata of the canvas in order to pick out each pixel of that text.
I want to pick the following from the pixel: x position, y position and its color. Then I would like to loop over that array with those pixels so I can draw back the text pixel by pixel so I have full control of each pixel, and can for example animate them.
However, I dont get it as smooth as I want. Look at my attach image, and you see the difference between the top text and then the text I've plotted out using fillRect for each pixel. Any help on how to make the new text look like the "fillText" text does?
Thanks
UPDATE: Added my code
var _particles = [];
var _canvas, _ctx, _width, _height;
(function(){
init();
})();
function init(){
setupParticles(getTextCanvasData());
}
function getTextCanvasData(){
// var w = 300, h = 150, ratio = 2;
_canvas = document.getElementById("textCanvas");
// _canvas.width = w * ratio;
// _canvas.height = h * ratio;
// _canvas.style.width = w + "px";
// _canvas.style.height = h + "px";
_ctx = _canvas.getContext("2d");
_ctx.fillStyle = "rgb(0, 154, 253)";
// _ctx.setTransform(ratio, 0, 0, ratio, 0, 0);
var str = "stackoverflow";
_ctx.font = "32px EB Garamond";
_ctx.fillText(str,0,23);
_width = _canvas.width;
_height = _canvas.height;
var data32 = new Uint32Array(_ctx.getImageData(0, 0, _width, _height).data.buffer);
var positions = [];
for(i = 0; i < data32.length; i++) {
if (data32[i] & 0xffff0000) {
positions.push({
x: (i % _width),
y: ((i / _width)|0),
});
}
}
return positions;
}
function setupParticles(positions){
var i = positions.length;
var particles = [];
while(i--){
var p = new Particle();
p.init(positions[i]);
_particles.push(p);
drawParticle(p);
}
}
function drawParticle(particle){
var x = particle.x;
var y = particle.y;
_ctx.beginPath();
_ctx.fillRect(x, y, 1, 1);
_ctx.fillStyle = 'green';
}
function Particle(){
this.init = function(pos){
this.x = pos.x;
this.y = pos.y + 30;
this.x0 = this.x;
this.y0 = this.y;
this.xDelta = 0;
this.yDelta = 0;
}
}

Here is an update to your code that reuses the alpha component of each pixel. There will still be some detail lost because we do not keep the antialiasing of the pixels (which in effect alters the actual color printed), but for this example the alpha is enough.
var _particles = [];
var _canvas, _ctx, _width, _height;
(function(){
init();
})();
function init(){
setupParticles(getTextCanvasData());
}
function getTextCanvasData(){
// var w = 300, h = 150, ratio = 2;
_canvas = document.getElementById("textCanvas");
// _canvas.width = w * ratio;
// _canvas.height = h * ratio;
// _canvas.style.width = w + "px";
// _canvas.style.height = h + "px";
_ctx = _canvas.getContext("2d");
_ctx.imageSmoothingEnabled= false;
_ctx.fillStyle = "rgb(0, 154, 253)";
// _ctx.setTransform(ratio, 0, 0, ratio, 0, 0);
var str = "stackoverflow";
_ctx.font = "32px EB Garamond";
_ctx.fillText(str,0,23);
_width = _canvas.width;
_height = _canvas.height;
var pixels = _ctx.getImageData(0, 0, _width, _height).data;
var data32 = new Uint32Array(pixels.buffer);
var positions = [];
for(i = 0; i < data32.length; i++) {
if (data32[i] & 0xffff0000) {
positions.push({
x: (i % _width),
y: ((i / _width)|0),
a: pixels[i*4 + 3] / 255
});
}
}
return positions;
}
function setupParticles(positions){
var i = positions.length;
var particles = [];
while(i--){
var p = new Particle();
p.init(positions[i]);
_particles.push(p);
drawParticle(p);
}
}
function drawParticle(particle){
var x = particle.x;
var y = particle.y;
_ctx.beginPath();
_ctx.fillStyle = `rgba(0,128,0,${particle.alpha})`;
_ctx.fillRect(x, y, 1, 1);
}
function Particle(){
this.init = function(pos){
this.x = pos.x;
this.y = pos.y + 30;
this.x0 = this.x;
this.y0 = this.y;
this.xDelta = 0;
this.yDelta = 0;
this.alpha = pos.a;
}
}
<canvas id="textCanvas"></canvas>

EaselJS how to update text

I'm trying to update the circles and text above each circle when mouseoveer event happens, however I only successfully update the circles, but not sure about how to update the text.
for (var i = 0; i < 100; i++) {
var circle = new createjs.Shape();
var r = 7;
var x = window.innerWidth * Math.random();
var y = window.innerHeight * Math.random();
var color = colors[Math.floor(i % colors.length)];
var alpha = 0.2 + Math.random() * 0.5;
circle.color = color;
circle.alpha = alpha;
circle.radius = r;
circle.graphics.beginFill(color).drawCircle(0, 0, r);
circle.x = x;
circle.y = y;
var txt = new createjs.Text(i.toString(), "11px Arial", "#FFF");
txt.x = x - 4;
txt.y = y - 18;
var con = new createjs.Container();
con.addChild(circle, txt);
con.addEventListener("mouseover", function(event) {
event.target.graphics.clear().beginFill(event.target.color).drawCircle(0, 0, 15).endFill();
event.target.text = "dsfasd";
stage.update(event);
});
stage.addChild(con);
}

In your listener, target refers to the container itself. But event.target.text is not a reference to the text object added as a child inside it. In order to access the second child, you need to do event.target.children[1].

Create color gradient describing discrete distribution of points

I am making a map that renders position of game objects (Project Zomboid zombies):
As user zooms out, single dots are no longer useful. Instead, I'd like to render distribution of zombies on an area using red color gradient. I tried to loop over all zombies for every rendered pixel and color it reciprocally to the sum of squared distances to the zombies. The result:
That's way too blurry. Also the results are more influenced by the zombies that are AWAY from the points - I need to influence them more by the zombies that are CLOSE. So what this is is just math. Here's the code I used:
var h = canvas.height;
var w = canvas.width;
// To loop over more than 1 pixel (performance)
var tileSize = 10;
var halfRadius = Math.floor(tileSize/2);
var time = performance.now();
// "Squared" because we didnt unsquare it
function distanceSquared(A, B) {
return (A.x-B.x)*(A.x-B.x)+(A.y-B.y)*(A.y-B.y);
}
// Loop for every x,y pixel (or region of pixels)
for(var y=0; y<h; y+=tileSize) {
for(var x=0; x<w; x+=tileSize) {
// Time security - stop rendering after 1 second
if(performance.now()-time>1000) {
x=w;y=h;break;
}
// Convert relative canvas offset to absolute point on the map
var point = canvasPixeltoImagePixel(x, y);
// For every zombie add sqrt(distance from this point to zombie)
var distancesRoot = 0;
// Loop over the zombies
var zombieCoords;
for(var i=0; i<zombies_length; i++) {
// Get single zombie coordinates as {x:0, y:0}
if((coords=zombies[i].pixel)==null)
coords = zombies[i].pixel = tileToPixel(zombies[i].coordinates[0], zombies[i].coordinates[1], drawer);
// square root is a) slow and b) probably not what I want anyway
var dist = distanceSquared(coords, point);
distancesRoot+=dist;
}
// The higher the sum of distances is, the more intensive should the color be
var style = 'rgba(255,0,0,'+300000000/distancesRoot+')';
// Kill the console immediatelly
//console.log(style);
// Maybe we should sample and cache the transparency styles since there's limited ammount of colors?
ctx.fillStyle = style;
ctx.fillRect(x-halfRadius,y-halfRadius,tileSize,tileSize);
}
}
I'm pretty fine with theoretical explanation how to do it, though if you make simple canvas example with some points, what would be awesome.

This is an example of a heat map. It's basically gradient orbs over points and then ramping the opacity through a heat ramp. The more orbs cluster together the more solid the color which can be shown as an amplified region with the proper ramp.
update
I cleaned up the variables a bit and put the zeeks in an animation loop. There's an fps counter to see how it's performing. The gradient circles can be expensive. We could probably do bigger worlds if we downscale the heat map. It won't be as smooth looking but will compute a lot faster.
update 2
The heat map now has an adjustable scale and as predicted we get an increase in fps.
if (typeof app === "undefined") {
var app = {};
}
app.zeeks = 200;
app.w = 600;
app.h = 400;
app.circleSize = 50;
app.scale = 0.25;
init();
function init() {
app.can = document.getElementById('can');
app.ctx = can.getContext('2d');
app.can.height = app.h;
app.can.width = app.w;
app.radius = Math.floor(app.circleSize / 2);
app.z = genZ(app.zeeks, app.w, app.h);
app.flip = false;
// Make temporary layer once.
app.layer = document.createElement('canvas');
app.layerCtx = app.layer.getContext('2d');
app.layer.width = Math.floor(app.w * app.scale);
app.layer.height = Math.floor(app.h * app.scale);
// Make the gradient canvas once.
var sCircle = Math.floor(app.circleSize * app.scale);
app.radius = Math.floor(sCircle / 2);
app.gCan = genGradientCircle(sCircle);
app.ramp = genRamp();
// fps counter
app.frames = 0;
app.fps = "- fps";
app.fpsInterval = setInterval(calcFps, 1000);
// start animation
ani();
flicker();
}
function calcFps() {
app.fps = app.frames + " fps";
app.frames = 0;
}
// animation loop
function ani() {
app.frames++;
var ctx = app.ctx;
var w = app.w;
var h = app.h;
moveZ();
//ctx.clearRect(0, 0, w, h);
ctx.fillStyle = "#006600";
ctx.fillRect(0, 0, w, h);
if (app.flip) {
drawZ2();
drawZ();
} else {
drawZ2();
}
ctx.fillStyle = "#FFFF00";
ctx.fillText(app.fps, 10, 10);
requestAnimationFrame(ani);
}
function flicker() {
app.flip = !app.flip;
if (app.flip) {
setTimeout(flicker, 500);
} else {
setTimeout(flicker, 5000);
}
}
function genGradientCircle(size) {
// gradient image
var gCan = document.createElement('canvas');
gCan.width = gCan.height = size;
var gCtx = gCan.getContext('2d');
var radius = Math.floor(size / 2);
var grad = gCtx.createRadialGradient(radius, radius, radius, radius, radius, 0);
grad.addColorStop(1, "rgba(255,255,255,.65)");
grad.addColorStop(0, "rgba(255,255,255,0)");
gCtx.fillStyle = grad;
gCtx.fillRect(0, 0, gCan.width, gCan.height);
return gCan;
}
function genRamp() {
// Create heat gradient
var heat = document.createElement('canvas');
var hCtx = heat.getContext('2d');
heat.width = 256;
heat.height = 5;
var linGrad = hCtx.createLinearGradient(0, 0, heat.width, heat.height);
linGrad.addColorStop(1, "rgba(255,0,0,.75)");
linGrad.addColorStop(0.5, "rgba(255,255,0,.03)");
linGrad.addColorStop(0, "rgba(255,255,0,0)");
hCtx.fillStyle = linGrad;
hCtx.fillRect(0, 0, heat.width, heat.height);
// create ramp from gradient
var ramp = [];
var imageData = hCtx.getImageData(0, 0, heat.width, 1);
var d = imageData.data;
for (var x = 0; x < heat.width; x++) {
var i = x * 4;
ramp[x] = [d[i], d[i + 1], d[i + 2], d[i + 3]];
}
return ramp;
}
function genZ(n, w, h) {
var a = [];
for (var i = 0; i < n; i++) {
a[i] = [
Math.floor(Math.random() * w),
Math.floor(Math.random() * h),
Math.floor(Math.random() * 3) - 1,
Math.floor(Math.random() * 3) - 1
];
}
return a;
}
function moveZ() {
var w = app.w
var h = app.h;
var z = app.z;
for (var i = 0; i < z.length; i++) {
var s = z[i];
s[0] += s[2];
s[1] += s[3];
if (s[0] > w || s[0] < 0) s[2] *= -1;
if (s[1] > w || s[1] < 0) s[3] *= -1;
}
}
function drawZ() {
var ctx = app.ctx;
var z = app.z;
ctx.fillStyle = "#FFFF00";
for (var i = 0; i < z.length; i++) {
ctx.fillRect(z[i][0] - 2, z[i][1] - 2, 4, 4);
}
}
function drawZ2() {
var ctx = app.ctx;
var layer = app.layer;
var layerCtx = app.layerCtx;
var gCan = app.gCan;
var z = app.z;
var radius = app.radius;
// render gradients at coords onto layer
for (var i = 0; i < z.length; i++) {
var x = Math.floor((z[i][0] * app.scale) - radius);
var y = Math.floor((z[i][1] * app.scale) - radius);
layerCtx.drawImage(gCan, x, y);
}
// adjust layer for heat ramp
var ramp = app.ramp;
// apply ramp to layer
var imageData = layerCtx.getImageData(0, 0, layer.width, layer.height);
d = imageData.data;
for (var i = 0; i < d.length; i += 4) {
if (d[i + 3] != 0) {
var c = ramp[d[i + 3]];
d[i] = c[0];
d[i + 1] = c[1];
d[i + 2] = c[2];
d[i + 3] = c[3];
}
}
layerCtx.putImageData(imageData, 0, 0);
// draw layer on world
ctx.drawImage(layer, 0, 0, layer.width, layer.height, 0, 0, app.w, app.h);
}
<canvas id="can" width="600" height="400"></canvas>

dynamic rectangles on canvas

I'm trying to make each rectangle in this fiddle to move up and down so it looks like a music equalizer. I wants the bars to animate up and down, and have absolutely no idea how to do animations. Fiddles would really help :)
http://jsfiddle.net/kiransh/1jqhznt6/
HTML
<canvas id="myCanvas" height="100"> </canvas>
JavaScript
var width = 8;
var distance = 3;
var c = document.getElementById("myCanvas");
var ctx = c.getContext("2d");
ctx.canvas.width = window.innerWidth;
var total = ctx.canvas.width;
var max = total/2+52;
var min = total/2-60;
ctx.fillStyle = "black";
ctx.globalAlpha=0.3;
for(var x = 0; x<total; x+=12)
{
if(x<= max && x>=min)
{
var height= Math.floor(Math.random()*40)+5;
}
else
{
var height= Math.floor(Math.random()*100)+5;
}
ctx.fillRect(x,100-height,width,height);
}

I don't know if this is the effect you need, but it should help you to start.
requestAnimationFrame is used to execute draw() at each frame. Each bar is re-defined after the specified delay, and then goes down.
var width = 8;
var distance = 3;
var c = document.getElementById("myCanvas");
var ctx = c.getContext("2d");
ctx.canvas.width = window.innerWidth;
var total = ctx.canvas.width;
var max = total/2+52;
var min = total/2-60;
ctx.fillStyle = "black";
ctx.globalAlpha=0.3;
var bars = [];
var barsCount = Math.floor(total / 12);
var barsLastRefreshTime = null;
var barsRefreshInterval = 500;
setInterval(function() {
for(var i = 0; i<barsCount; i++) {
var x = i * 12;
if(x<= max && x>=min) {
var height= Math.floor(Math.random()*40)+5;
} else {
var height= Math.floor(Math.random()*100)+5;
}
bars[i] = height;
}
barsLastRefreshTime = (new Date()).getTime();
}, barsRefreshInterval);
function draw() {
var currentTime = (new Date()).getTime();
var timePassedRate = (barsRefreshInterval - (currentTime - barsLastRefreshTime)) / barsRefreshInterval;
ctx.clearRect(0,0,c.width,c.height);
for(var i = 0; i<bars.length; i++) {
var x = i * 12;
var height = bars[i] * timePassedRate;
ctx.fillRect(x,100-height,width,height);
}
requestAnimationFrame(draw);
}
draw();
(I can't find a way to save the fiddle ?!?)

You need to use a tick function to update your canvas. You can use requestAnimationFrame() and choose a time interval you'd like to animate on (you can determine this using Date.now()).
Then, keep a list of your bars and change their height. Then re-render it to your canvas.
Here is some quick hacky code...
var width = 8;
var distance = 3;
var c = document.getElementById("myCanvas");
var ctx = c.getContext("2d");
ctx.canvas.width = window.innerWidth;
var total = ctx.canvas.width;
var max = total / 2 + 52;
var min = total / 2 - 60;
ctx.fillStyle = "black";
ctx.globalAlpha = 0.3;
var lastDrawTime = Date.now();
var draw = function () {
if (Date.now() - lastDrawTime < 60) {
return webkitRequestAnimationFrame(draw);
}
ctx.clearRect(0, 0, c.width, c.height);
for (var x = 0; x < total; x += 12) {
if (x <= max && x >= min) {
var height = Math.floor(Math.random() * 40) + 5;
} else {
var height = Math.floor(Math.random() * 100) + 5;
}
ctx.fillRect(x, 100 - height, width, height);
}
lastDrawTime = Date.now();
webkitRequestAnimationFrame(draw);
};
draw();

To do animation you have to clear the canvas and redraw the rectangles in their new position at each frame, using either setInterval() or setTimeout() or requestAnimationFrame().
The best is to use requestAnimationFrame() for adapation of frames per second.