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HTML

              
                <canvas
  width="100"
  height="100"
  id="canvas"
></canvas>
              
            
!

CSS

              
                body {
  height: 100vh;
  display: flex;
  justify-content: center;
  align-items: center;
  background: #000;
}

canvas {
  vertical-align: middle;
  image-rendering: pixelated;
  width: 90vmin;
  height: 90vmin;
}
              
            
!

JS

              
                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 drawPlanet(ctx, width, state) {
  const {
    size,
    colors,
    atmosphereThickness,
    atmosphereColor,
    mapShiftSize,
    mapShiftSpeed,
    map
  } = Settings.planet

  const {
    mapShift,
    mapShiftDirection,
    mapShiftCounter
  } = state.planet

  // atmosphere
  const radius = width * size / 2
  ctx.fillStyle = atmosphereColor
  ctx.beginPath()
  ctx.arc(
    width / 2,
    width / 2,
    radius * atmosphereThickness,
    0,
    2 * π
  )
  ctx.fill()

  // planet circle
  ctx.fillStyle = colors.base
  ctx.beginPath()
  ctx.arc(
    width / 2,
    width / 2,
    radius,
    0,
    2 * π
  )
  ctx.fill()

  // clipping path
  ctx.save()
  ctx.beginPath()
  ctx.arc(
    width / 2,
    width / 2,
    radius,
    0,
    2 * π
  )
  ctx.clip()

  // radial gradient for shiny ocean surface
  const gradient = ctx.createRadialGradient(
    width / 2 + radius / 4,
    width / 2 - radius / 4,
    radius / 4,
    width / 2,
    width / 2,
    radius * 1.25
  )
  gradient.addColorStop(0, rgba(150, 150, 255, .2))
  gradient.addColorStop(1, 'transparent')
  ctx.fillStyle = gradient
  ctx.fillRect(
    width / 2 - (size * width) / 2,
    width / 2 - (size * width) / 2,
    size * width,
    size * width
  )

  // Map
  const mapPxSizeX = size * width / (map.length - mapShiftSize)
  const mapPxSizeY = size * width / map.length
  map.forEach((row, mapY) => {
    row.forEach((cell, mapX) => {
      const middleRow = map.length / 2
      const shift = abs( middleRow - abs(middleRow - mapY) ) / middleRow
      const globularShift = sin(π / 2 * shift)
      ctx.fillStyle = colors[cell]
      ctx.fillRect(
        mapShift * globularShift + width / 2 - floor(map.length / 2 * mapPxSizeX) + mapX * mapPxSizeX,
        width / 2 - floor(map.length / 2 * mapPxSizeY) + mapY * mapPxSizeY,
        mapPxSizeX,
        mapPxSizeY
      )
    })
  })

  // Back and forth movement of the map
  if (!(mapShiftCounter % (1/mapShiftSpeed))) {
    state.planet.mapShift += mapShiftDirection
    if (abs(state.planet.mapShift) - mapShiftSize >= 0) {
      state.planet.mapShiftDirection *= -1
    }
  }
  state.planet.mapShiftCounter++

  // restore for clipping path
  ctx.restore()
}

function drawMoonBack(ctx, width, state) {
  const { size, color } = Settings.moonBack
  const { orbit } = state.moonBack
  const radius = width * size / 2
  ctx.fillStyle = color
  ctx.beginPath()
  ctx.arc(
    orbit * width + size * width,
    width / 2,
    radius,
    0,
    2 * π
  )
  ctx.fill()
}

function drawMoon(ctx, width, state) {
  const { size, color, craters, craterColor } = Settings.moon
  const { orbit } = state.moon
  const radius = width * size / 2
  const moonX = orbit * width - size * width
  ctx.fillStyle = color
  ctx.beginPath()
  ctx.arc(
    moonX,
    width / 2,
    radius,
    0,
    2 * π
  )
  ctx.fill()
  ctx.fillStyle = craterColor
  craters.forEach(({ x, y, size: craterSize }) => {
    ctx.beginPath()
    const craterX = moonX - (size / 2 * width) + x * radius
    const craterY = width / 2 - (size / 2 * width) + y * radius
    ctx.arc(
      craterX - size * 15 + size * 30 * orbit,
      craterY,
      radius * craterSize,
      0,
      2 * π
    )
    ctx.fill()
  })
}

function orbitMoon(ctx, width, state) {
  if (state.moon.orbit > 2) {
    state.moonBack.orbit -= (width * state.moonBack.orbitSpeed)
    if (state.moonBack.orbit < -.66) {
      state.moon.orbit = 0
      state.moonBack.orbit = 1
    }
  } else {
    state.moon.orbit += (width * state.moon.orbitSpeed)
  }
}

function draw(ctx, width, state) {
  generateStars(ctx, width, state)
  drawSky(ctx, width, state)
  drawStars(ctx, width, state)
  drawMoonBack(ctx, width, state)
  drawPlanet(ctx, width, state)
  drawMoon(ctx, width, state)
  orbitMoon(ctx, width, state)
  requestAnimationFrame(() => {
    draw(ctx, width, state)
  })
}

function init(state) {
  const ctx = canvas.getContext('2d')
  draw(ctx, canvas.width, state)
}

const Settings = {
  debug: false,
  planet: {
    size: .2,
    colors: {
      base: 'darkblue',
      0: 'transparent',
      1: 'forestgreen',
      2: '#eee',
      3: 'khaki'
    },
    atmosphereThickness: 1.2,
    atmosphereColor: rgba(100, 100, 255, .1),
    mapShiftSize: 3,
    mapShiftSpeed: .1,
    map: [
      [ 0, 0, 0, 0, 0, 2, 2, 0, 0, 0, 0, 0, 0, 0 ],
      [ 0, 0, 1, 2, 0, 0, 1, 1, 1, 0, 0, 0, 0, 0 ],
      [ 0, 1, 1, 1, 0, 0, 0, 0, 0, 1, 1, 0, 0, 1 ],
      [ 0, 1, 1, 0, 0, 0, 0, 1, 0, 1, 1, 1, 0, 0 ],
      [ 0, 0, 0, 0, 0, 0, 0, 0, 1, 3, 3, 1, 0, 0 ],
      [ 1, 0, 0, 0, 0, 0, 0, 0, 0, 1, 3, 1, 0, 1 ],
      [ 0, 0, 0, 0, 1, 1, 1, 0, 0, 0, 1, 1, 0, 1 ],
      [ 0, 1, 0, 1, 1, 3, 1, 0, 0, 0, 0, 0, 0, 0 ],
      [ 0, 0, 0, 1, 1, 3, 1, 0, 0, 0, 0, 1, 1, 0 ],
      [ 0, 0, 0, 0, 1, 1, 1, 1, 0, 0, 0, 0, 1, 0 ],
      [ 0, 0, 0, 0, 0, 0, 1, 1, 0, 0, 0, 0, 0, 0 ],
      [ 0, 0, 0, 0, 0, 2, 0, 0, 0, 0, 1, 0, 0, 0 ],
      [ 0, 0, 0, 0, 0, 2, 2, 2, 0, 0, 0, 0, 0, 0 ],
      [ 0, 0, 0, 0, 0, 0, 2, 0, 0, 0, 0, 0, 0, 0 ]
    ]
  },
  moonBack: {
    size: .03,
    color: '#aaa'
  },
  moon: {
    size: .06,
    color: '#ccc',
    craterColor: '#555',
    craters: [
      { x: .6, y: .6, size: .3 },
      { x: 1.1, y: 1, size: .3 },
      { x: 1.5, y: .8, size: .2 }
    ]
  },
  sky: {
    bg: '#05080c',
    get shiftSpeed() {
      if (Settings.debug) return 0.8
      return 0.08
    },
    starDensity: 0.04,
    get starColor() {
      if (random() >= .25) {
        return rgba([ 255, 255, 255, .1 ])
      }
      if (random() >= .75) {
        return rgba([ 255, 255, 255, .3 ])
      }
      if (random() >= .66) {
        return rgba([ 255, 200, 200, .3 ])
      }
      if (random() >= .5) {
        return rgba([ 200, 200, 255, .3 ])
      }
      if (random() >= .33) {
        return rgba([ 255, 200, 200, .4 ])
      }
      if (random() >= .25) {
        return '#fff'
      }
      return rgba([ 200, 200, 255, .4 ])
    }
  }
}

const State = {
  planet: {
    mapShift: 0,
    mapShiftDirection: 1,
    mapShiftCounter: 0
  },
  moonBack: {
    orbit: 1,
    get orbitSpeed() {
      if (Settings.debug) return .0001
      return .00001
    }
  },
  moon: {
    orbit: .25,
    get orbitSpeed() {
      if (Settings.debug) return .0002
      return .00002
    }
  },
  sky: {
    shift: 0,
    fields: 0,
    stars: []
  }
}

init(State)
              
            
!
999px

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