javascript - 使 JavaScript 画布背景透明

Question

我试图让这个 Codepen 的背景透明https://codepen.io/scorch/pen/BZjbmW。我想让漩涡在不同的背景上，而不是在规定的 Codepen 上的彩色背景。

我试过添加 css 代码，但似乎没有做任何事情。我尝试弄乱 Canvas RGB，但似乎也没有做任何事情。

// 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]
  }
}

标签： javascript

Answer 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]
  }
}