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Am trying to make the background of this Codepen transparent https://codepen.io/scorch/pen/BZjbmW. I would like to have the Swirls on the a different backgrounds, instead of the colored background that is on the stated Codepen.
I have tried add css code but that did not seem to do anything. I tried messing with the Canvas RGB and that did not seem to do anything either.
// create a canvas element
var canvas = document.createElement("canvas")
// attach element to DOM
document.getElementsByTagName("body")[0].appendChild(canvas)
// background color [r, g, b]
var bg = [20, 0, 30]
var wh = window.innerHeight
// get the canvas context (this is the part we draw to)
var ctx = canvas.getContext("2d")
function setup() {
// setup the canvas size to match the window
canvas.width = window.innerWidth
canvas.height = window.innerHeight
wh = window.innerWidth < window.innerHeight ? window.innerWidth : window.innerHeight
// set the 0,0 point to the middle of the canvas, this is not necessary but it can be handy
ctx.translate(canvas.width / 2, canvas.height / 2)
fill(bg, 1)
}
// fill entire canvas with a preset color
function fill(rgb, amt) {
ctx.beginPath(); // start path
ctx.rect(-canvas.width / 2, -canvas.height / 2, canvas.width, canvas.height) // set rectangle to be the same size as the window
ctx.fillStyle = `rgba(${rgb[0]}, ${rgb[1]}, ${rgb[2]}, ${amt})` // use the rgb array/color for fill, and amt for opacity
ctx.fill() // do the drawing
}
function drawCircle(x, y, r, color) {
ctx.beginPath()
ctx.arc(x, y, r, 0, 2 * Math.PI)
ctx.fillStyle = color || 'white'
ctx.fill()
ctx.closePath()
}
function Particle() {
// initialize loopers with random trange and offset
this.loop1 = new Looper(500 + 200 * Math.random(), 860 * Math.random())
this.loop2 = new Looper(320 + 70 * Math.random(), 20 * Math.random())
this.loop3 = new Looper(120 + 20 * Math.random(), 140 * Math.random())
this.history = []
this.history_max = 40
// this.x = null
// this.y = null
this.offset = Math.random() // some color offset for the color
this.draw = function() {
// set x,y, radius, and color params
var x = this.loop1.sin * (wh / 4 - 10) + this.loop2.sin * (wh / 6 - 10) + this.loop3.sin * 60
var y = this.loop1.cos * (wh / 4 - 10) + this.loop2.cos * (wh / 6 - 10) + this.loop3.cos * 10
var r = 0.2 + 3 * this.loop3.sinNorm * this.loop3.cosNorm // set the radius
var c = `hsla(${280 + 60 * (this.loop3.cosNorm + this.offset) * this.loop2.sinNorm}, ${100}%, ${50 + 10 * this.loop3.sin}%, ${1})`
ctx.beginPath()
ctx.strokeStyle = c
ctx.lineCap = 'round'
ctx.lineWidth = r
var tx = x
var ty = y
for (var i = 0; i < Math.min(this.history_max * this.loop3.cosNorm, this.history.length); i++) {
ctx.moveTo(tx, ty)
tx = this.history[i][0]
ty = this.history[i][1]
ctx.lineTo(tx, ty)
}
ctx.stroke()
drawCircle(x, y, r * 2 + 3, c); // draw the circle
this.loop1.update() // update looper
this.loop2.update() // update looper
this.loop3.update() // update looper
this.history.unshift([x, y])
if (this.history.length > this.history_max) {
this.history.pop()
}
}
}
// initialize a set of particle
var particles = []
for (var i = 0; i < 90; i++) {
particles.push(new Particle())
}
function draw() {
// fill context with background color
fill(bg, 0.36)
// update all the particles
for (var i = 0; i < particles.length; i++) {
particles[i].draw() // do it once
}
// this is a draw loop, this will execute frequently and is comparable to EnterFrame on other platform
window.requestAnimationFrame(function() {
draw()
})
}
// start enterFrame loop
window.requestAnimationFrame(draw);
// force running setup
setup()
// re-setup canvas when the size of the window changes
window.addEventListener("resize", setup)
// create a class to hold value and have built in incrementing functionality
function Looper(steps, start) {
this.val = start || 0 // set value to start value if defined, or 1
this.steps = steps || 100 // set steps to passed value or default to 100
this.norm = this.val / this.range // initialize normalized value (between 0 and 1)
this.sin = Math.sin(this.norm * Math.PI * 2) // get sine value from norm normalized to [0, 2PI]
this.sinNorm = (this.sin + 1) / 2 // normalize sin to [0,1]
this.cos = Math.cos(this.norm * Math.PI * 2) // get cosine value from norm normalized to [0, 2PI]
this.cosNorm = (this.cos + 1) / 2 // normalize cos to [0,1]
this.update = function() {
this.val = (this.val + 1) % this.steps // update value
this.norm = this.val / this.steps // update normalize value (between 0 and 1)
this.sin = Math.sin(this.norm * Math.PI * 2) // get sine value from norm normalized to [0, 2PI]
this.sinNorm = (this.sin + 1) / 2 // normalize sine to [0,1]
this.cos = Math.cos(this.norm * Math.PI * 2) // get cosine value from norm normalized to [0, 2PI]
this.cosNorm = (this.cos + 1) / 2 // normalize cos to [0,1]
}
}
ctx.fillStyle = rgba(255,255,255,0)
// create a canvas element
var canvas = document.createElement("canvas")
// attach element to DOM
document.getElementsByTagName("body")[0].appendChild(canvas)
// background color [r, g, b]
var bg = [20, 0, 30]
var wh = window.innerHeight
// get the canvas context (this is the part we draw to)
var ctx = canvas.getContext("2d")
function setup() {
// setup the canvas size to match the window
canvas.width = window.innerWidth
canvas.height = window.innerHeight
wh = window.innerWidth < window.innerHeight ? window.innerWidth : window.innerHeight
// set the 0,0 point to the middle of the canvas, this is not necessary but it can be handy
ctx.translate(canvas.width / 2, canvas.height / 2)
fill(bg, 1)
}
// fill entire canvas with a preset color
function fill(rgb, amt) {
ctx.beginPath(); // start path
ctx.rect(-canvas.width / 2, -canvas.height / 2, canvas.width, canvas.height) // set rectangle to be the same size as the window
ctx.fillStyle = `rgba(255,255,255,0)` // use the rgb array/color for fill, and amt for opacity
ctx.fill() // do the drawing
}
function drawCircle(x, y, r, color) {
ctx.beginPath()
ctx.arc(x, y, r, 0, 2 * Math.PI)
ctx.fillStyle = color || 'white'
ctx.fill()
ctx.closePath()
}
function Particle() {
// initialize loopers with random trange and offset
this.loop1 = new Looper(500 + 200 * Math.random(), 860 * Math.random())
this.loop2 = new Looper(320 + 70 * Math.random(), 20 * Math.random())
this.loop3 = new Looper(120 + 20 * Math.random(), 140 * Math.random())
this.history = []
this.history_max = 40
// this.x = null
// this.y = null
this.offset = Math.random() // some color offset for the color
this.draw = function() {
// set x,y, radius, and color params
var x = this.loop1.sin * (wh / 4 - 10) + this.loop2.sin * (wh / 6 - 10) + this.loop3.sin * 60
var y = this.loop1.cos * (wh / 4 - 10) + this.loop2.cos * (wh / 6 - 10) + this.loop3.cos * 10
var r = 0.2 + 3 * this.loop3.sinNorm * this.loop3.cosNorm // set the radius
var c = `hsla(${280 + 60 * (this.loop3.cosNorm + this.offset) * this.loop2.sinNorm}, ${100}%, ${50 + 10 * this.loop3.sin}%, ${1})`
ctx.beginPath()
ctx.strokeStyle = c
ctx.lineCap = 'round'
ctx.lineWidth = r
var tx = x
var ty = y
for (var i = 0; i < Math.min(this.history_max * this.loop3.cosNorm, this.history.length); i++) {
ctx.moveTo(tx, ty)
tx = this.history[i][0]
ty = this.history[i][1]
ctx.lineTo(tx, ty)
}
ctx.stroke()
drawCircle(x, y, r * 2 + 3, c); // draw the circle
this.loop1.update() // update looper
this.loop2.update() // update looper
this.loop3.update() // update looper
this.history.unshift([x, y])
if (this.history.length > this.history_max) {
this.history.pop()
}
}
}
// initialize a set of particle
var particles = []
for (var i = 0; i < 90; i++) {
particles.push(new Particle())
}
function draw() {
// fill context with background color
fill(bg, 0.36)
// update all the particles
for (var i = 0; i < particles.length; i++) {
particles[i].draw() // do it once
}
// this is a draw loop, this will execute frequently and is comparable to EnterFrame on other platform
window.requestAnimationFrame(function() {
draw()
})
}
// start enterFrame loop
window.requestAnimationFrame(draw);
// force running setup
setup()
// re-setup canvas when the size of the window changes
window.addEventListener("resize", setup)
// create a class to hold value and have built in incrementing functionality
function Looper(steps, start) {
this.val = start || 0 // set value to start value if defined, or 1
this.steps = steps || 100 // set steps to passed value or default to 100
this.norm = this.val / this.range // initialize normalized value (between 0 and 1)
this.sin = Math.sin(this.norm * Math.PI * 2) // get sine value from norm normalized to [0, 2PI]
this.sinNorm = (this.sin + 1) / 2 // normalize sin to [0,1]
this.cos = Math.cos(this.norm * Math.PI * 2) // get cosine value from norm normalized to [0, 2PI]
this.cosNorm = (this.cos + 1) / 2 // normalize cos to [0,1]
this.update = function() {
this.val = (this.val + 1) % this.steps // update value
this.norm = this.val / this.steps // update normalize value (between 0 and 1)
this.sin = Math.sin(this.norm * Math.PI * 2) // get sine value from norm normalized to [0, 2PI]
this.sinNorm = (this.sin + 1) / 2 // normalize sine to [0,1]
this.cos = Math.cos(this.norm * Math.PI * 2) // get cosine value from norm normalized to [0, 2PI]
this.cosNorm = (this.cos + 1) / 2 // normalize cos to [0,1]
}
}
I created simple tilemap using Tiled (3200 x 3200 pixels). I loaded it on my canvas using this library
I draw entire tilemap 3200 x 3200 60 times per seocnd.
I tried to move around and it works fine. Btw, I move around canvas using ctx.translate. I included this in my own function
But when I created bigger map in Tiled ( 32000 x 32000 pixels ) - I got a very freezing page. I couldn't move around fast, I think there was about 10 fps
So how to fix it? I have to call drawTiles() function 60 times per second. But is there any way to draw only visible part of the tile? Like draw only what I see on my screen (0, 0, monitorWidth, monitorHeight I guess)
Thank you
##Drawing a large tileset
If you have a large tile set and only see part of it in the canvas you just need to calculate the tile at the top left of the canvas and the number of tiles across and down that will fit the canvas.
Then draw the square array of tiles that fit the canvas.
In the example the tile set is 1024 by 1024 tiles (worldTileCount = 1024), each tile is 64 by 64 pixels tileSize = 64, making the total playfield 65536 pixels square
The position of the top left tile is set by the variables worldX, worldY
###Function to draw tiles
// val | 0 is the same as Math.floor(val)
var worldX = 512 * tileSize; // pixel position of playfield
var worldY = 512 * tileSize;
function drawWorld(){
const c = worldTileCount; // get the width of the tile array
const s = tileSize; // get the tile size in pixels
// get the tile position
const tx = worldX / s | 0; // get the top left tile
const ty = worldY / s | 0;
// get the number of tiles that will fit the canvas
const tW = (canvas.width / s | 0) + 2;
const tH = (canvas.height / s | 0) + 2;
// set the location. Must floor to pixel boundary or you get holes
ctx.setTransform(1,0,0,1,-worldX | 0,-worldY | 0);
// Draw the tiles across and down
for(var y = 0; y < tH; y += 1){
for(var x = 0; x < tW; x += 1){
// get the index into the tile array for the tile at x,y plus the topleft tile
const i = tx + x + (ty + y) * c;
// get the tile id from the tileMap. If outside map default to tile 6
const tindx = tileMap[i] === undefined ? 6 : tileMap[i];
// draw the tile at its location. last 2 args are x,y pixel location
imageTools.drawSpriteQuick(tileSet, tindx, (tx + x) * s, (ty + y) * s);
}
}
}
###setTransform and absolute coordinates.
Use absolute coordinates makes everything simple.
Use the canvas context setTransform to set the world position and then each tile can be drawn at its own coordinate.
// set the world location. The | 0 floors the values and ensures no holes
ctx.setTransform(1,0,0,1,-worldX | 0,-worldY | 0);
That way if you have a character at position 51023, 34256 you can just draw it at that location.
playerX = 51023;
playerY = 34256;
ctx.drawImage(myPlayerImage,playerX,playerY);
If you want the tile map relative to the player then just set the world position to be half the canvas size up and to the left plus one tile to ensure overlap
playerX = 51023;
playerY = 34256;
worldX = playerX - canvas.width / 2 - tileWidth;
worldY = playerY - canvas.height / 2 - tileHeight;
###Demo of large 65536 by 65536 pixel tile map.
At 60fps if you have the horses and can handle much much bigger without any frame rate loss. (map size limit using this method is approx 4,000,000,000 by 4,000,000,000pixels (32 bit integers coordinates))
#UPDATE 15/5/2019 re Jitter
The comments have pointed out that there is some jitter as the map scrolls.
I have made changes to smooth out the random path with a strong ease in out turn every 240 frame (4 seconds at 60fps) Also added a frame rate reducer, if you click and hold the mouse button on the canvas the frame rate will be slowed to 1/8th normal so that the jitter is easier to see.
There are two reasons for the jitter.
###Time error
The first and least is the time passed to the update function by requestAnimationFrame, the interval is not perfect and rounding errors due to the time is compounding the alignment problems.
To reduce the time error I have set the move speed to a constant interval to minimize the rounding error drift between frames.
###Aligning tiles to pixels
The main reason for the jitter is that the tiles must be rendered on pixel boundaries. If not then aliasing errors will create visible seams between tiles.
To see the difference click the button top left to toggle pixel alignment on and off.
To get smooth scrolling (sub pixel positioning) draw the map to an offscreen canvas aligning to the pixels, then render that canvas to the display canvas adding the sub pixel offset. That will give the best possible result using the canvas. For better you will need to use webGL
###End of update
var refereshSkip = false; // when true drops frame rate by 4
var dontAlignToPixel = false;
var ctx = canvas.getContext("2d");
function mouseEvent(e) {
if(e.type === "click") {
dontAlignToPixel = !dontAlignToPixel;
pixAlignInfo.textContent = dontAlignToPixel ? "Pixel Align is OFF" : "Pixel Align is ON";
} else {
refereshSkip = e.type === "mousedown";
}
}
pixAlignInfo.addEventListener("click",mouseEvent);
canvas.addEventListener("mousedown",mouseEvent);
canvas.addEventListener("mouseup",mouseEvent);
// wait for code under this to setup
setTimeout(() => {
var w = canvas.width;
var h = canvas.height;
var cw = w / 2; // center
var ch = h / 2;
// create tile map
const worldTileCount = 1024;
const tileMap = new Uint8Array(worldTileCount * worldTileCount);
// add random tiles
doFor(worldTileCount * worldTileCount, i => {
tileMap[i] = randI(1, tileCount);
});
// this is the movement direction of the map
var worldDir = Math.PI / 4;
/* =======================================================================
Drawing the tileMap
========================================================================*/
var worldX = 512 * tileSize;
var worldY = 512 * tileSize;
function drawWorld() {
const c = worldTileCount; // get the width of the tile array
const s = tileSize; // get the tile size in pixels
const tx = worldX / s | 0; // get the top left tile
const ty = worldY / s | 0;
const tW = (canvas.width / s | 0) + 2; // get the number of tiles to fit canvas
const tH = (canvas.height / s | 0) + 2;
// set the location
if(dontAlignToPixel) {
ctx.setTransform(1, 0, 0, 1, -worldX,-worldY);
} else {
ctx.setTransform(1, 0, 0, 1, Math.floor(-worldX),Math.floor(-worldY));
}
// Draw the tiles
for (var y = 0; y < tH; y += 1) {
for (var x = 0; x < tW; x += 1) {
const i = tx + x + (ty + y) * c;
const tindx = tileMap[i] === undefined ? 6 : tileMap[i];
imageTools.drawSpriteQuick(tileSet, tindx, (tx + x) * s, (ty + y) * s);
}
}
}
var timer = 0;
var refreshFrames = 0;
const dirChangeMax = 3.5;
const framesBetweenDirChange = 240;
var dirChangeDelay = 1;
var dirChange = 0;
var prevDir = worldDir;
const eCurve = (v, p = 2) => v < 0 ? 0 : v > 1 ? 1 : v ** p / (v ** p + (1 - v) ** p);
//==============================================================
// main render function
function update() {
refreshFrames ++;
if(!refereshSkip || (refereshSkip && refreshFrames % 8 === 0)){
timer += 1000 / 60;
ctx.setTransform(1, 0, 0, 1, 0, 0); // reset transform
ctx.globalAlpha = 1; // reset alpha
if (w !== innerWidth || h !== innerHeight) {
cw = (w = canvas.width = innerWidth) / 2;
ch = (h = canvas.height = innerHeight) / 2;
} else {
ctx.clearRect(0, 0, w, h);
}
// Move the map
var speed = Math.sin(timer / 10000) * 8;
worldX += Math.cos(worldDir) * speed;
worldY += Math.sin(worldDir) * speed;
if(dirChangeDelay-- <= 0) {
dirChangeDelay = framesBetweenDirChange;
prevDir = worldDir = prevDir + dirChange;
dirChange = rand(-dirChangeMax , dirChangeMax);
}
worldDir = prevDir + (1-eCurve(dirChangeDelay / framesBetweenDirChange,3)) * dirChange;
// Draw the map
drawWorld();
}
requestAnimationFrame(update);
}
requestAnimationFrame(update);
}, 0);
/*===========================================================================
CODE FROM HERE DOWN UNRELATED TO THE ANSWER
===========================================================================*/
const imageTools = (function() {
// This interface is as is. No warenties no garenties, and NOT to be used comercialy
var workImg, workImg1, keep; // for internal use
keep = false;
var tools = {
canvas(width, height) { // create a blank image (canvas)
var c = document.createElement("canvas");
c.width = width;
c.height = height;
return c;
},
createImage: function(width, height) {
var i = this.canvas(width, height);
i.ctx = i.getContext("2d");
return i;
},
drawSpriteQuick: function(image, spriteIndex, x, y) {
var w, h, spr;
spr = image.sprites[spriteIndex];
w = spr.w;
h = spr.h;
ctx.drawImage(image, spr.x, spr.y, w, h, x, y, w, h);
},
line(x1, y1, x2, y2) {
ctx.moveTo(x1, y1);
ctx.lineTo(x2, y2);
},
circle(x, y, r) {
ctx.moveTo(x + r, y);
ctx.arc(x, y, r, 0, Math.PI * 2);
},
};
return tools;
})();
const doFor = (count, cb) => {
var i = 0;
while (i < count && cb(i++) !== true);
}; // the ; after while loop is important don't remove
const randI = (min, max = min + (min = 0)) => (Math.random() * (max - min) + min) | 0;
const rand = (min = 1, max = min + (min = 0)) => Math.random() * (max - min) + min;
const seededRandom = (() => {
var seed = 1;
return {
max: 2576436549074795,
reseed(s) {
seed = s
},
random() {
return seed = ((8765432352450986 * seed) + 8507698654323524) % this.max
}
}
})();
const randSeed = (seed) => seededRandom.reseed(seed | 0);
const randSI = (min, max = min + (min = 0)) => (seededRandom.random() % (max - min)) + min;
const randS = (min = 1, max = min + (min = 0)) => (seededRandom.random() / seededRandom.max) * (max - min) + min;
const tileSize = 64;
const tileCount = 7;
function drawGrass(ctx, c1, c2, c3) {
const s = tileSize;
const gs = s / (8 * c3);
ctx.fillStyle = c1;
ctx.fillRect(0, 0, s, s);
ctx.strokeStyle = c2;
ctx.lineWidth = 2;
ctx.lineCap = "round";
ctx.beginPath();
doFor(s, i => {
const x = rand(-gs, s + gs);
const y = rand(-gs, s + gs);
const x1 = rand(x - gs, x + gs);
const y1 = rand(y - gs, y + gs);
imageTools.line(x, y, x1, y1);
imageTools.line(x + s, y, x1 + s, y1);
imageTools.line(x - s, y, x1 - s, y1);
imageTools.line(x, y + s, x1, y1 + s);
imageTools.line(x, y - s, x1, y1 - s);
})
ctx.stroke();
}
function drawTree(ctx, c1, c2, c3) {
const seed = Date.now();
const s = tileSize;
const gs = s / 2;
const gh = gs / 2;
ctx.fillStyle = c1;
ctx.strokeStyle = "#000";
ctx.lineWidth = 2;
ctx.save();
ctx.shadowColor = "rgba(0,0,0,0.5)";
ctx.shadowBlur = 4;
ctx.shadowOffsetX = 8;
ctx.shadowOffsetY = 8;
randSeed(seed);
ctx.beginPath();
doFor(18, i => {
const ss = 1 - i / 18;
imageTools.circle(randS(gs - gh * ss, gs + gh * ss), randS(gs - gh * ss, gs + gh * ss), randS(gh / 4, gh / 2));
})
ctx.stroke();
ctx.fill();
ctx.restore();
ctx.fillStyle = c2;
ctx.strokeStyle = c3;
ctx.lineWidth = 2;
ctx.save();
randSeed(seed);
ctx.beginPath();
doFor(18, i => {
const ss = 1 - i / 18;
imageTools.circle(randS(gs - gh * ss, gs + gh * ss) - 2, randS(gs - gh * ss, gs + gh * ss) - 2, randS(gh / 4, gh / 2) / 1.6);
})
ctx.stroke();
ctx.fill();
ctx.restore();
}
const tileRenders = [
(ctx) => {
drawGrass(ctx, "#4C4", "#4F4", 1)
},
(ctx) => {
drawGrass(ctx, "#644", "#844", 2)
},
(ctx) => {
tileRenders[0](ctx);
drawTree(ctx, "#480", "#8E0", "#7C0")
},
(ctx) => {
tileRenders[1](ctx);
drawTree(ctx, "#680", "#AE0", "#8C0")
},
(ctx) => {
drawGrass(ctx, "#008", "#00A", 4)
},
(ctx) => {
drawGrass(ctx, "#009", "#00C", 4)
},
(ctx) => {
drawGrass(ctx, "#00B", "#00D", 4)
},
]
const tileSet = imageTools.createImage(tileSize * tileCount, tileSize);
const ctxMain = ctx;
ctx = tileSet.ctx;
tileSet.sprites = [];
doFor(tileCount, i => {
x = i * tileSize;
ctx.save();
ctx.setTransform(1, 0, 0, 1, x, 0);
ctx.beginPath();
ctx.rect(0, 0, tileSize, tileSize);
ctx.clip()
if (tileRenders[i]) {
tileRenders[i](ctx)
}
tileSet.sprites.push({
x,
y: 0,
w: tileSize,
h: tileSize
});
ctx.restore();
});
ctx = ctxMain;
canvas {
position: absolute;
top: 0px;
left: 0px;
}
div {
position: absolute;
top: 8px;
left: 8px;
color: white;
}
#pixAlignInfo {
color: yellow;
cursor: pointer;
border: 2px solid green;
margin: 4px;
}
#pixAlignInfo:hover {
color: white;
background: #0008;
cursor: pointer;
}
body {
background: #49c;
}
<canvas id="canvas"></canvas>
<div>Hold left button to slow to 1/8th<br>
<span id="pixAlignInfo">Click this button to toggle pixel alignment. Alignment is ON</span></div>
I'm trying to create a hyperdrive effect, like from Star Wars, where the stars have a motion trail. I've gotten as far as creating the motion trail on a single circle, it still looks like the trail is going down in the y direction and not forwards or positive in the z direction.
Also, how could I do this with (many) randomly placed circles as if they were stars?
My code is on jsfiddle (https://jsfiddle.net/5m7x5zxu/) and below:
var canvas = document.querySelector("canvas");
var context = canvas.getContext("2d");
var xPos = 180;
var yPos = 100;
var motionTrailLength = 16;
var positions = [];
function storeLastPosition(xPos, yPos) {
// push an item
positions.push({
x: xPos,
y: yPos
});
//get rid of first item
if (positions.length > motionTrailLength) {
positions.pop();
}
}
function update() {
context.clearRect(0, 0, canvas.width, canvas.height);
for (var i = positions.length-1; i > 0; i--) {
var ratio = (i - 1) / positions.length;
drawCircle(positions[i].x, positions[i].y, ratio);
}
drawCircle(xPos, yPos, "source");
var k=2;
storeLastPosition(xPos, yPos);
// update position
if (yPos > 125) {
positions.pop();
}
else{
yPos += k*1.1;
}
requestAnimationFrame(update);
}
update();
function drawCircle(x, y, r) {
if (r == "source") {
r = 1;
} else {
r*=1.1;
}
context.beginPath();
context.arc(x, y, 3, 0, 2 * Math.PI, true);
context.fillStyle = "rgba(255, 255, 255, " + parseFloat(1-r) + ")";
context.fill();
}
Canvas feedback and particles.
This type of FX can be done many ways.
You could just use a particle systems and draw stars (as lines) moving away from a central point, as the speed increase you increase the line length. When at low speed the line becomes a circle if you set ctx.lineWidth > 1 and ctx.lineCap = "round"
To add to the FX you can use render feedback as I think you have done by rendering the canvas over its self. If you render it slightly larger you get a zoom FX. If you use ctx.globalCompositeOperation = "lighter" you can increase the stars intensity as you speed up to make up for the overall loss of brightness as stars move faster.
Example
I got carried away so you will have to sift through the code to find what you need.
The particle system uses the Point object and a special array called bubbleArray to stop GC hits from janking the animation.
You can use just an ordinary array if you want. The particles are independent of the bubble array. When they have moved outside the screen they are move to a pool and used again when a new particle is needed. The update function moves them and the draw Function draws them I guess LOL
The function loop is the main loop and adds and draws particles (I have set the particle count to 400 but should handle many more)
The hyper drive is operated via the mouse button. Press for on, let go for off. (It will distort the text if it's being displayed)
The canvas feedback is set via that hyperSpeed variable, the math is a little complex. The sCurce function just limits the value to 0,1 in this case to stop alpha from going over or under 1,0. The hyperZero is just the sCurve return for 1 which is the hyper drives slowest speed.
I have pushed the feedback very close to the limit. In the first few lines of the loop function you can set the top speed if(mouse.button){ if(hyperSpeed < 1.75){ Over this value 1.75 and you will start to get bad FX, at about 2 the whole screen will just go white (I think that was where)
Just play with it and if you have questions ask in the comments.
const ctx = canvas.getContext("2d");
// very simple mouse
const mouse = {x : 0, y : 0, button : false}
function mouseEvents(e){
mouse.x = e.pageX;
mouse.y = e.pageY;
mouse.button = e.type === "mousedown" ? true : e.type === "mouseup" ? false : mouse.button;
}
["down","up","move"].forEach(name => document.addEventListener("mouse"+name,mouseEvents));
// High performance array pool using buubleArray to separate pool objects and active object.
// This is designed to eliminate GC hits involved with particle systems and
// objects that have short lifetimes but used often.
// Warning this code is not well tested.
const bubbleArray = () => {
const items = [];
var count = 0;
return {
clear(){ // warning this dereferences all locally held references and can incur Big GC hit. Use it wisely.
this.items.length = 0;
count = 0;
},
update() {
var head, tail;
head = tail = 0;
while(head < count){
if(items[head].update() === false) {head += 1 }
else{
if(tail < head){
const temp = items[head];
items[head] = items[tail];
items[tail] = temp;
}
head += 1;
tail += 1;
}
}
return count = tail;
},
createCallFunction(name, earlyExit = false){
name = name.split(" ")[0];
const keys = Object.keys(this);
if(Object.keys(this).indexOf(name) > -1){ throw new Error(`Can not create function name '${name}' as it already exists.`) }
if(!/\W/g.test(name)){
let func;
if(earlyExit){
func = `var items = this.items; var count = this.getCount(); var i = 0;\nwhile(i < count){ if (items[i++].${name}() === true) { break } }`;
}else{
func = `var items = this.items; var count = this.getCount(); var i = 0;\nwhile(i < count){ items[i++].${name}() }`;
}
!this.items && (this.items = items);
this[name] = new Function(func);
}else{ throw new Error(`Function name '${name}' contains illegal characters. Use alpha numeric characters.`) }
},
callEach(name){var i = 0; while(i < count){ if (items[i++][name]() === true) { break } } },
each(cb) { var i = 0; while(i < count){ if (cb(items[i], i++) === true) { break } } },
next() { if (count < items.length) { return items[count ++] } },
add(item) {
if(count === items.length){
items.push(item);
count ++;
}else{
items.push(items[count]);
items[count++] = item;
}
return item;
},
getCount() { return count },
}
}
// Helpers rand float, randI random Int
// doFor iterator
// sCurve curve input -Infinity to Infinity out -1 to 1
// randHSLA creates random colour
// CImage, CImageCtx create image and image with context attached
const randI = (min, max = min + (min = 0)) => (Math.random() * (max - min) + min) | 0;
const rand = (min = 1, max = min + (min = 0)) => Math.random() * (max - min) + min;
const doFor = (count, cb) => { var i = 0; while (i < count && cb(i++) !== true); }; // the ; after while loop is important don't remove
const sCurve = (v,p) => (2 / (1 + Math.pow(p,-v))) -1;
const randHSLA = (h, h1, s = 100, s1 = 100, l = 50, l1 = 50, a = 1, a1 = 1) => { return `hsla(${randI(h,h1) % 360},${randI(s,s1)}%,${randI(l,l1)}%,${rand(a,a1)})` }
const CImage = (w = 128, h = w) => (c = document.createElement("canvas"),c.width = w,c.height = h, c);
const CImageCtx = (w = 128, h = w) => (c = CImage(w,h), c.ctx = c.getContext("2d"), c);
// create image to hold text
var textImage = CImageCtx(1024, 1024);
var c = textImage.ctx;
c.fillStyle = "#FF0";
c.font = "64px arial black";
c.textAlign = "center";
c.textBaseline = "middle";
const text = "HYPER,SPEED FX,VII,,Battle of Jank,,Hold the mouse,button to increase,speed.".split(",");
text.forEach((line,i) => { c.fillText(line,512,i * 68 + 68) });
const maxLines = text.length * 68 + 68;
function starWarIntro(image,x1,y1,x2,y2,pos){
var iw = image.width;
var ih = image.height;
var hh = (x2 - x1) / (y2 - y1); // Slope of left edge
var w2 = iw / 2; // half width
var z1 = w2 - x1; // Distance (z) to first line
var z2 = (z1 / (w2 - x2)) * z1 - z1; // distance (z) between first and last line
var sk,t3,t3a,z3a,lines, z3, dd = 0, a = 0, as = 2 / (y2 - y1);
for (var y = y1; y < y2 && dd < maxLines; y++) { // for each line
t3 = ((y - y1) * hh) + x1; // get scan line top left edge
t3a = (((y+1) - y1) * hh) + x1; // get scan line bottom left edge
z3 = (z1 / (w2 - t3)) * z1; // get Z distance to top of this line
z3a = (z1 / (w2 - t3a)) * z1; // get Z distance to bottom of this line
dd = ((z3 - z1) / z2) * ih; // get y bitmap coord
a += as;
ctx.globalAlpha = a < 1 ? a : 1;
dd += pos; // kludge for this answer to make text move
// does not move text correctly
lines = ((z3a - z1) / z2) * ih-dd; // get number of lines to copy
ctx.drawImage(image, 0, dd , iw, lines, t3, y, w - t3 * 2, 1.5);
}
}
// canvas settings
var w = canvas.width;
var h = canvas.height;
var cw = w / 2; // center
var ch = h / 2;
// diagonal distance used to set point alpha (see point update)
var diag = Math.sqrt(w * w + h * h);
// If window size is changed this is called to resize the canvas
// It is not called via the resize event as that can fire to often and
// debounce makes it feel sluggish so is called from main loop.
function resizeCanvas(){
points.clear();
canvas.width = innerWidth;
canvas.height = innerHeight;
w = canvas.width;
h = canvas.height;
cw = w / 2; // center
ch = h / 2;
diag = Math.sqrt(w * w + h * h);
}
// create array of points
const points = bubbleArray();
// create optimised draw function itterator
points.createCallFunction("draw",false);
// spawns a new star
function spawnPoint(pos){
var p = points.next();
p = points.add(new Point())
if (p === undefined) { p = points.add(new Point()) }
p.reset(pos);
}
// point object represents a single star
function Point(pos){ // this function is duplicated as reset
if(pos){
this.x = pos.x;
this.y = pos.y;
this.dead = false;
}else{
this.x = 0;
this.y = 0;
this.dead = true;
}
this.alpha = 0;
var x = this.x - cw;
var y = this.y - ch;
this.dir = Math.atan2(y,x);
this.distStart = Math.sqrt(x * x + y * y);
this.speed = rand(0.01,1);
this.col = randHSLA(220,280,100,100,50,100);
this.dx = Math.cos(this.dir) * this.speed;
this.dy = Math.sin(this.dir) * this.speed;
}
Point.prototype = {
reset : Point, // resets the point
update(){ // moves point and returns false when outside
this.speed *= hyperSpeed; // increase speed the more it has moved
this.x += Math.cos(this.dir) * this.speed;
this.y += Math.sin(this.dir) * this.speed;
var x = this.x - cw;
var y = this.y - ch;
this.alpha = (Math.sqrt(x * x + y * y) - this.distStart) / (diag * 0.5 - this.distStart);
if(this.alpha > 1 || this.x < 0 || this.y < 0 || this.x > w || this.h > h){
this.dead = true;
}
return !this.dead;
},
draw(){ // draws the point
ctx.strokeStyle = this.col;
ctx.globalAlpha = 0.25 + this.alpha *0.75;
ctx.beginPath();
ctx.lineTo(this.x - this.dx * this.speed, this.y - this.dy * this.speed);
ctx.lineTo(this.x, this.y);
ctx.stroke();
}
}
const maxStarCount = 400;
const p = {x : 0, y : 0};
var hyperSpeed = 1.001;
const alphaZero = sCurve(1,2);
var startTime;
function loop(time){
if(startTime === undefined){
startTime = time;
}
if(w !== innerWidth || h !== innerHeight){
resizeCanvas();
}
// if mouse down then go to hyper speed
if(mouse.button){
if(hyperSpeed < 1.75){
hyperSpeed += 0.01;
}
}else{
if(hyperSpeed > 1.01){
hyperSpeed -= 0.01;
}else if(hyperSpeed > 1.001){
hyperSpeed -= 0.001;
}
}
var hs = sCurve(hyperSpeed,2);
ctx.globalAlpha = 1;
ctx.setTransform(1,0,0,1,0,0); // reset transform
//==============================================================
// UPDATE the line below could be the problem. Remove it and try
// what is under that
//==============================================================
//ctx.fillStyle = `rgba(0,0,0,${1-(hs-alphaZero)*2})`;
// next two lines are the replacement
ctx.fillStyle = "Black";
ctx.globalAlpha = 1-(hs-alphaZero) * 2;
//==============================================================
ctx.fillRect(0,0,w,h);
// the amount to expand canvas feedback
var sx = (hyperSpeed-1) * cw * 0.1;
var sy = (hyperSpeed-1) * ch * 0.1;
// increase alpha as speed increases
ctx.globalAlpha = (hs-alphaZero)*2;
ctx.globalCompositeOperation = "lighter";
// draws feedback twice
ctx.drawImage(canvas,-sx, -sy, w + sx*2 , h + sy*2)
ctx.drawImage(canvas,-sx/2, -sy/2, w + sx , h + sy)
ctx.globalCompositeOperation = "source-over";
// add stars if count < maxStarCount
if(points.getCount() < maxStarCount){
var cent = (hyperSpeed - 1) *0.5; // pulls stars to center as speed increases
doFor(10,()=>{
p.x = rand(cw * cent ,w - cw * cent); // random screen position
p.y = rand(ch * cent,h - ch * cent);
spawnPoint(p)
})
}
// as speed increases make lines thicker
ctx.lineWidth = 2 + hs*2;
ctx.lineCap = "round";
points.update(); // update points
points.draw(); // draw points
ctx.globalAlpha = 1;
// scroll the perspective star wars text FX
var scrollTime = (time - startTime) / 5 - 2312;
if(scrollTime < 1024){
starWarIntro(textImage,cw - h * 0.5, h * 0.2, cw - h * 3, h , scrollTime );
}
requestAnimationFrame(loop);
}
requestAnimationFrame(loop);
canvas { position : absolute; top : 0px; left : 0px; }
<canvas id="canvas"></canvas>
Here's another simple example, based mainly on the same idea as Blindman67, concetric lines moving away from center at different velocities (the farther from center, the faster it moves..) also no recycling pool here.
"use strict"
var c = document.createElement("canvas");
document.body.append(c);
var ctx = c.getContext("2d");
var w = window.innerWidth;
var h = window.innerHeight;
var ox = w / 2;
var oy = h / 2;
c.width = w; c.height = h;
const stars = 120;
const speed = 0.5;
const trailLength = 90;
ctx.fillStyle = "#000";
ctx.fillRect(0, 0, w, h);
ctx.fillStyle = "#fff"
ctx.fillRect(ox, oy, 1, 1);
init();
function init() {
var X = [];
var Y = [];
for(var i = 0; i < stars; i++) {
var x = Math.random() * w;
var y = Math.random() * h;
X.push( translateX(x) );
Y.push( translateY(y) );
}
drawTrails(X, Y)
}
function translateX(x) {
return x - ox;
}
function translateY(y) {
return oy - y;
}
function getDistance(x, y) {
return Math.sqrt(x * x + y * y);
}
function getLineEquation(x, y) {
return function(n) {
return y / x * n;
}
}
function drawTrails(X, Y) {
var count = 1;
ctx.fillStyle = "#000";
ctx.fillRect(0, 0, w, h);
function anim() {
for(var i = 0; i < X.length; i++) {
var x = X[i];
var y = Y[i];
drawNextPoint(x, y, count);
}
count+= speed;
if(count < trailLength) {
window.requestAnimationFrame(anim);
}
else {
init();
}
}
anim();
}
function drawNextPoint(x, y, step) {
ctx.fillStyle = "#fff";
var f = getLineEquation(x, y);
var coef = Math.abs(x) / 100;
var dist = getDistance( x, y);
var sp = speed * dist / 100;
for(var i = 0; i < sp; i++) {
var newX = x + Math.sign(x) * (step + i) * coef;
var newY = translateY( f(newX) );
ctx.fillRect(newX + ox, newY, 1, 1);
}
}
body {
overflow: hidden;
}
canvas {
position: absolute;
left: 0;
top: 0;
}
I'm starting with a canvas element. I'm making the left half red, and the right side blue. Every half second, setInterval calls a function, scramble, which splits both RHS and LHS into pieces, and shuffles them.
Here is a fiddle: https://jsfiddle.net/aeq1g3yb/
The code is below. The reason I'm using window.onload is because this thing is supposed to scramble pictures and I want the pictures to load first. I'm using colors here because of the cross-origin business that I don't know enough about, so this is my accommodation.
var n = 1;
var v = 1;
function scramble() {
//get the canvas and change its width
var c = document.getElementById("myCanvas");
c.width = 600;
var ctx = c.getContext("2d");
//drawing 2 different colors side by side
ctx.fillStyle = "red";
ctx.fillRect(0, 0, c.width/2, c.height);
ctx.fillStyle = "blue";
ctx.fillRect(c.width/2, 0, c.width/2, c.height);
//how big will each shuffled chunk be
var stepsA = (c.width/2) / n;
var stepsB = (c.width/2) / n;
var step = stepsA + stepsB;
var imgDataA = [];
var imgDataB = [];
for (var i = 0; i < n; i++) {
var imgDataElementA = ctx.getImageData(stepsA*i, 0, stepsA, c.height);
var imgDataElementB = ctx.getImageData(c.width/2+stepsB*i, 0, stepsB, c.height);
imgDataA.push(imgDataElementA);
imgDataB.push(imgDataElementB);
}
//clearing out the canvas before laying on the new stuff
ctx.fillStyle = "white";
ctx.fillRect(0, 0, c.width, c.height);
//put the images back
for (var i = 0; i < n; i++) {
ctx.putImageData(imgDataA[i], step*i, 0);
ctx.putImageData(imgDataB[i], step*i+stepsA, 0);
}
//gonna count the steps
var count = document.getElementById("count");
count.innerHTML = n;
n += v;
if (n >= 100 || n <= 1) {
v *= -1;
}
}; //closing function scramble
window.onload = function() { //gotta do this bc code executes before image loads
scramble();
};
window.setInterval(scramble, 500);
More or less, this thing works the way I want it to. But there is one problem: Sometimes there are vertical white lines.
My question is:
Why are there white lines? If you view the fiddle, you will see the degree to which this impairs the effect of the shuffle.
You can`t divide a Pixel
The problem can be solve but will introduce some other artifacts as you can not divide integer pixels into fractions.
Quick solution
The following solution for your existing code rounds down for the start of a section and up for the width.
for (var i = 0; i < n; i++) {
var imgDataElementA = ctx.getImageData(
Math.floor(stepsA * i), 0,
Math.ceil(stepsA + stepsA * i) - Math.floor(stepsA * i), c.height
);
var imgDataElementB = ctx.getImageData(
Math.floor(c.width / 2 + stepsB * i), 0,
Math.ceil(c.width / 2 + stepsB * i + stepsB) - Math.floor(c.width / 2 + stepsB * i), c.height);
imgDataA.push(imgDataElementA);
imgDataB.push(imgDataElementB);
}
Quicker options
But doing this via the pixel image data is about the slowest possible way you could find to do it. You can just use the 2D context.imageDraw function to do the movement for you. Or if you want the best in terms of performance a WebGL solution would be the best with the fragment shader doing the scrambling for you as a parallel solution.
There is no perfect solution
But in the end you can not cut a pixel in half, there are a wide range of ways to attempt to solve this but each method has its own artifacts. Ideally you should only slice an image if the rule image.width % slices === 0 in all other cases you will have one or more slices that will not fit on an integer number of pixels.
Example of 4 rounding methods.
The demo shows 4 different methods and with 2 colors. Mouse over to see a closer view. Each method is separated horizontally with a white line. Hold the mouse button to increase the slice counter.
The top is your original.
The next three are 3 different ways of dealing with the fractional pixel width.
const mouse = {x : 0, y : 0, button : false}
function mouseEvents(e){
const m = mouse;
if(m.element){
m.bounds = m.element.getBoundingClientRect();
m.x = e.pageX - m.bounds.left - scrollX;
m.y = e.pageY - m.bounds.top - scrollY;
m.button = e.type === "mousedown" ? true : e.type === "mouseup" ? false : m.button;
}
}
["down","up","move"].forEach(name => document.addEventListener("mouse"+name,mouseEvents));
const counterElement = document.getElementById("count");
// get constants for the demo
const c = document.getElementById("myCanvas");
mouse.element = c;
// The image with the blue and red
const img = document.createElement("canvas");
// the zoom image overlay
const zoom = document.createElement("canvas");
// the scrambled image
const scram = document.createElement("canvas");
// Set sizes and get context
const w = scram.width = zoom.width = img.width = c.width = 500;
const h = scram.height = zoom.height = img.height = c.height;
const dCtx = c.getContext("2d"); // display context
const iCtx = img.getContext("2d"); // source image context
const zCtx = zoom.getContext("2d"); // zoom context
const sCtx = scram.getContext("2d"); // scrambled context
// some constants
const zoomAmount = 4;
const zoomRadius = 60;
const framesToStep = 10;
function createTestPattern(ctx){
ctx.fillStyle = "red";
ctx.fillRect(0, 0, c.width/2, c.height/2);
ctx.fillStyle = "blue";
ctx.fillRect(c.width/2, 0, c.width/2, c.height/2);
ctx.fillStyle = "black";
ctx.fillRect(0, c.height/2, c.width/2, c.height/2);
ctx.fillStyle = "#CCC";
ctx.fillRect(c.width/2, c.height/2, c.width/2, c.height/2);
}
createTestPattern(iCtx);
sCtx.drawImage(iCtx.canvas, 0, 0);
// Shows a zoom area so that blind men like me can see what is going on.
function showMouseZoom(src,dest,zoom = zoomAmount,radius = zoomRadius){
dest.clearRect(0,0,w,h);
dest.imageSmoothingEnabled = false;
if(mouse.x >= 0 && mouse.y >= 0 && mouse.x < w && mouse.y < h){
dest.setTransform(zoom,0,0,zoom,mouse.x,mouse.y)
dest.drawImage(src.canvas, -mouse.x, -mouse.y);
dest.setTransform(1,0,0,1,0,0);
dest.globalCompositeOperation = "destination-in";
dest.beginPath();
dest.arc(mouse.x,mouse.y,radius,0,Math.PI * 2);
dest.fill();
dest.globalCompositeOperation = "source-over";
dest.lineWidth = 4;
dest.strokeStyle = "black";
dest.stroke();
}
}
function scramble(src,dest,y,height) {
const w = src.canvas.width;
const h = src.canvas.height;
const steps = (w/2) / slices;
dest.fillStyle = "white";
dest.fillRect(0, y, w, height);
for (var i = 0; i < slices * 2; i++) {
dest.drawImage(src.canvas,
((i / 2) | 0) * steps + (i % 2) * (w / 2)- 0.5, y,
steps + 1, height,
i * steps - 0.5, y,
steps+ 1, height
);
}
}
function scrambleFloor(src,dest,y,height) {
const w = src.canvas.width;
const h = src.canvas.height;
const steps = (w/2) / slices;
dest.fillStyle = "white";
dest.fillRect(0, y, w, height);
for (var i = 0; i < slices * 2; i++) {
dest.drawImage(src.canvas,
(((i / 2) | 0) * steps + (i % 2) * (w / 2)- 0.5) | 0, y,
steps + 1, height,
(i * steps - 0.5) | 0, y,
steps + 1, height
);
}
}
function scrambleNoOverlap(src,dest,y,height) {
const w = src.canvas.width;
const h = src.canvas.height;
const steps = (w / 2) / slices;
dest.fillStyle = "white";
dest.fillRect(0, y, w, height);
for (var i = 0; i < slices * 2; i++) {
dest.drawImage(src.canvas,
((i / 2) | 0) * steps + (i % 2) * (w / 2), y,
steps, height,
i * steps - 0.5, y,
steps, height
);
}
}
function scrambleOriginal(src,dest,y,height) {
const w = src.canvas.width;
const h = src.canvas.height;
//how big will each shuffled chunk be
var stepsA = (w/2) / slices;
var stepsB = (w/2) / slices;
var step = stepsA + stepsB;
var imgDataA = [];
var imgDataB = [];
for (var i = 0; i < slices; i++) {
var imgDataElementA = src.getImageData(stepsA*i, y, stepsA, height);
var imgDataElementB = src.getImageData(w/2+stepsB*i, y, stepsB, height);
imgDataA.push(imgDataElementA);
imgDataB.push(imgDataElementB);
}
//clearing out the canvas before laying on the new stuff
dest.fillStyle = "white";
dest.fillRect(0, y, w, height);
//put the images back
for (var i = 0; i < slices; i++) {
dest.putImageData(imgDataA[i], step*i, y);
dest.putImageData(imgDataB[i], step*i+stepsA, y);
}
}; //closing function scramble
const scrambleMethods = [scrambleOriginal,scramble,scrambleFloor,scrambleNoOverlap];
var frameCount = 0;
var sliceStep = 1;
var slices = 1;
function mainLoop(){
if(mouse.button){
if(frameCount++ % framesToStep === framesToStep-1){ // every 30 Frames
slices += sliceStep;
if(slices > 150 || slices < 2){ sliceStep = -sliceStep }
counterElement.textContent = slices; // Prevent reflow by using textContent
sCtx.clearRect(0,0,w,h);
sCtx.imageSmoothingEnabled = true;
const len = scrambleMethods.length;
for(var i = 0; i < len; i ++){
scrambleMethods[i](iCtx,sCtx,(128/len) * i, 128/len-2);
scrambleMethods[i](iCtx,sCtx,(128/len) * i + 128, 128/len-2);
}
}
}
dCtx.fillStyle = "white";
dCtx.fillRect(0,0,w,h);
dCtx.drawImage(sCtx.canvas,0,0);
showMouseZoom(dCtx,zCtx);
dCtx.drawImage(zCtx.canvas,0,0);
requestAnimationFrame(mainLoop);
}
//scramble(iCtx,sCtx);
requestAnimationFrame(mainLoop);
canvas {
border: 1px solid black;
}
#count {
position : absolute;
top : 0px;
left : 10px;
font-family: monospace;
font-size: 20px;
}
<canvas id="myCanvas" height = "256" title="Hold mouse button to chance slice count"></canvas>
<p id="count"></p>
I am having trouble trying to set the canvas to fill the whole window. It is currently set to 500x500.. I am new to coding and would really appreciate any help! Thank you.
Here is the code:
<!DOCTYPE html>
<html>
<head>
<title>Starfield effect done in HTML 5</title>
<script>
window.onload = function() {
/* --- config start --- */
var starfieldCanvasId = "starfieldCanvas", // id of the canvas to use
framerate = 60, // frames per second this animation runs at (this is not exact)
numberOfStarsModifier = 0.15, // Number of stars, higher numbers have performance impact
flightSpeed = 0.003; // speed of the flight, the higher this number the faster
/* ---- config end ---- */
var canvas = document.getElementById(starfieldCanvasId),
context = canvas.getContext("2d"),
width = canvas.width,
height = canvas.height,
numberOfStars = width * height / 1000 * numberOfStarsModifier,
dirX = width / 2,
dirY = height / 2,
stars = [],
TWO_PI = Math.PI * 2;
// initialize starfield
for(var x = 0; x < numberOfStars; x++) {
stars[x] = {
x: range(0, width),
y: range(0, height),
size: range(0, 1)
};
}
// when mouse moves over canvas change middle point of animation
canvas.onmousemove = function(event) {
dirX = event.offsetX,
dirY = event.offsetY;
}
// start tick at specified fps
window.setInterval(tick, Math.floor(1000 / framerate));
// main routine
function tick() {
var oldX,
oldY;
// reset canvas for next frame
context.clearRect(0, 0, width, height);
for(var x = 0; x < numberOfStars; x++) {
// save old status
oldX = stars[x].x;
oldY = stars[x].y;
// calculate changes to star
stars[x].x += (stars[x].x - dirX) * stars[x].size * flightSpeed;
stars[x].y += (stars[x].y - dirY) * stars[x].size * flightSpeed;
stars[x].size += flightSpeed;
// if star is out of bounds, reset
if(stars[x].x < 0 || stars[x].x > width || stars[x].y < 0 || stars[x].y > height) {
stars[x] = {
x: range(0, width),
y: range(0, height),
size: 0
};
}
// draw star
context.strokeStyle = "rgba(255, 255, 255, " + Math.min(stars[x].size, 1) + ")";
context.lineWidth = stars[x].size;
context.beginPath();
context.moveTo(oldX, oldY);
context.lineTo(stars[x].x, stars[x].y);
context.stroke();
}
}
// get a random number inside a range
function range(start, end) {
return Math.random() * (end - start) + start;
}
};
</script>
</head>
<body style="background:#000;">
<canvas width="500" height="500" id="starfieldCanvas"></canvas>
</body>
</html>
Original code and credit to: https://www.timewasters-place.com/starfield-animation-done-in-html-5/
I assume you mean that you want your script to determine the screen size automatically, and then to set the canvas to be the full screen instead of the hardcoded 500 x 500 currently.
You can determine the viewport size programatically using the following where the width and height are as follows respectively. (Source):
var width = window.innerWidth
|| document.documentElement.clientWidth
|| document.body.clientWidth;
var height = window.innerHeight
|| document.documentElement.clientHeight
|| document.body.clientHeight;
Then you can set the dimensions of your canvas as follows:
canvas.width = width;
canvas.height = height;
So, this would be the full code in your case:
<!DOCTYPE html>
<html>
<head>
<title>Starfield effect done in HTML 5</title>
<script>
window.onload = function() {
/* --- config start --- */
var starfieldCanvasId = "starfieldCanvas", // id of the canvas to use
framerate = 60, // frames per second this animation runs at (this is not exact)
numberOfStarsModifier = 0.15, // Number of stars, higher numbers have performance impact
flightSpeed = 0.003; // speed of the flight, the higher this number the faster
var width = window.innerWidth
|| document.documentElement.clientWidth
|| document.body.clientWidth;
var height = window.innerHeight
|| document.documentElement.clientHeight
|| document.body.clientHeight;
/* ---- config end ---- */
var canvas = document.getElementById(starfieldCanvasId),
context = canvas.getContext("2d"),
stars = [],
TWO_PI = Math.PI * 2;
canvas.width = width;
canvas.height = height;
numberOfStars = width * height / 1000 * numberOfStarsModifier;
dirX = width / 2;
dirY = height / 2;
// initialize starfield
for(var x = 0; x < numberOfStars; x++) {
stars[x] = {
x: range(0, width),
y: range(0, height),
size: range(0, 1)
};
}
// when mouse moves over canvas change middle point of animation
canvas.onmousemove = function(event) {
dirX = event.offsetX,
dirY = event.offsetY;
}
// start tick at specified fps
window.setInterval(tick, Math.floor(1000 / framerate));
// main routine
function tick() {
var oldX,
oldY;
// reset canvas for next frame
context.clearRect(0, 0, width, height);
for(var x = 0; x < numberOfStars; x++) {
// save old status
oldX = stars[x].x;
oldY = stars[x].y;
// calculate changes to star
stars[x].x += (stars[x].x - dirX) * stars[x].size * flightSpeed;
stars[x].y += (stars[x].y - dirY) * stars[x].size * flightSpeed;
stars[x].size += flightSpeed;
// if star is out of bounds, reset
if(stars[x].x < 0 || stars[x].x > width || stars[x].y < 0 || stars[x].y > height) {
stars[x] = {
x: range(0, width),
y: range(0, height),
size: 0
};
}
// draw star
context.strokeStyle = "rgba(255, 255, 255, " + Math.min(stars[x].size, 1) + ")";
context.lineWidth = stars[x].size;
context.beginPath();
context.moveTo(oldX, oldY);
context.lineTo(stars[x].x, stars[x].y);
context.stroke();
}
}
// get a random number inside a range
function range(start, end) {
return Math.random() * (end - start) + start;
}
};
</script>
</head>
<body style="background:#000;">
<canvas id="starfieldCanvas"></canvas>
</body>
</html>
I also tested this on Fiddle. Here's the link: Fiddle
Hope this helps! Let me know if it works.