134 lines
3.0 KiB
JavaScript
134 lines
3.0 KiB
JavaScript
// https://codepen.io/pavlovsk/pen/VRbGVP
|
|
const { abs, floor, ceil, round, sin, PI: π } = Math;
|
|
const random = (x = 1) => Math.random() * x;
|
|
const rgb = (...values) => `rgb(${values.join(',')})`;
|
|
const rgba = (...values) => `rgba(${values.join(',')})`;
|
|
|
|
function nArray(n) {
|
|
return [...Array(n).keys()];
|
|
}
|
|
|
|
function generateGrid(size, cellCallback) {
|
|
return nArray(size).map((row, y) =>
|
|
nArray(size).map((cell, x) => cellCallback(x, y)));
|
|
|
|
}
|
|
|
|
function generateField({ density, offset = 0, width, height }) {
|
|
const pixels = nArray(width * height);
|
|
return pixels.
|
|
map((px, i) => {
|
|
const star = {
|
|
x: offset + px % width,
|
|
y: floor(px / width) };
|
|
|
|
// Put some colorful points if debug is enabled
|
|
if (Settings.debug) {
|
|
const isMiddle = i === width * height / 2;
|
|
const isLast = i === width * height - 1;
|
|
if (isLast) {
|
|
return Object.assign(star, { color: 'red' });
|
|
}
|
|
if (isMiddle) {
|
|
return Object.assign(star, { color: 'blue' });
|
|
}
|
|
}
|
|
if (random() > 1 - density) {
|
|
return star;
|
|
}
|
|
return null;
|
|
}).
|
|
filter(Boolean);
|
|
}
|
|
|
|
function drawSky(ctx, width, state) {
|
|
ctx.fillStyle = Settings.sky.bg;
|
|
ctx.fillRect(0, 0, width, width);
|
|
state.sky.shift += Settings.sky.shiftSpeed;
|
|
}
|
|
|
|
function generateStars(ctx, width, state) {
|
|
const { stars, fields, shift } = state.sky;
|
|
if (!stars.length || width * fields - shift <= width) {
|
|
const newStars = generateField({
|
|
density: Settings.sky.starDensity,
|
|
offset: width * fields,
|
|
width: width,
|
|
height: width }).
|
|
map(star => ({
|
|
...star,
|
|
color: star.color || Settings.sky.starColor }));
|
|
|
|
stars.splice(0, 1);
|
|
stars.push(...newStars);
|
|
state.sky.fields++;
|
|
}
|
|
}
|
|
|
|
function drawStars(ctx, width, state) {
|
|
const stars = state.sky.stars;
|
|
stars.forEach(({ x, y, color }) => {
|
|
ctx.fillStyle = color;
|
|
const shiftedX = x - state.sky.shift;
|
|
ctx.fillRect(shiftedX, y, 1, 1);
|
|
});
|
|
}
|
|
|
|
function draw(ctx, width, state) {
|
|
generateStars(ctx, width, state);
|
|
drawSky(ctx, width, state);
|
|
drawStars(ctx, width, state);
|
|
requestAnimationFrame(() => {
|
|
draw(ctx, width, state);
|
|
});
|
|
}
|
|
|
|
function init(state, canvas) {
|
|
const ctx = canvas.getContext('2d');
|
|
draw(ctx, canvas.width, state);
|
|
}
|
|
|
|
const Settings = {
|
|
debug: false,
|
|
sky: {
|
|
bg: '#f5f5f5',
|
|
get shiftSpeed() {
|
|
if (Settings.debug) return 0.8;
|
|
return 0.05;
|
|
},
|
|
starDensity: 0.1,
|
|
get starColor() {
|
|
if (random() >= .5) {
|
|
return 'black';
|
|
}
|
|
if (random() >= .66) {
|
|
return 'hotpink';
|
|
}
|
|
if (random() >= .66) {
|
|
return 'crimson';
|
|
}
|
|
if (random() >= .66) {
|
|
return 'mediumspringgreen';
|
|
}
|
|
if (random() >= .25) {
|
|
return '#fd5';
|
|
}
|
|
return 'palevioletred';
|
|
} } };
|
|
|
|
|
|
|
|
const State = {
|
|
sky: {
|
|
shift: 0,
|
|
fields: 0,
|
|
stars: [] } };
|
|
|
|
|
|
|
|
const image = new Image();
|
|
image.src = 'https://assets.codepen.io/25387/torni-clear-sm.png';
|
|
image.onload = () => {
|
|
init(State, canvas);
|
|
init(State, canvas2);
|
|
}; |