我在我的网站上实现此 ( https://codepen.io/ge1doot/pen/oXWepr) codepen 时遇到问题。我想像以前那样替换图像。我研究了数百万个关于使用 javascript 在 Canvas 上绘图的问题，但它们似乎都指向两种解决方案之一:CORS header 和设置导致 Canvas 受污染，或者它们没有 image.onload 函数. CORS 对我来说应该不是问题，因为图像位于同一台服务器上，而且我有一个 image.onload 函数。我正在使用的修改后的代码如下。
这一行尤其可能导致问题:
var canvas = ge1doot.canvas("canvas");
虽然我不知道。我不确定它到底在做什么，而且通过我数小时的阅读也无法完全弄明白。以我有限的理解，它可能与 document.getElementById 做同样的事情？而且，当我在 css 中更改它们的颜色时， Canvas 和背景显示得很好，只是图像本身没有显示。
HTML:
<!DOCTYPE html>
<html lang"en">
<head>
<meta charset="utf-8">
<link rel="stylesheet" type="text/css" href="parallax.css" />
<script type="text/javascript" src="https://ajax.googleapis.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<title>...</title>
</head>
<body>
<script type="text/javascript" script src="parallax.js"></script>
<canvas id="canvas"></canvas>
<div id="frame"></div>
</body>
</html>
CSS:
html {
overflow: hidden;
touch-action: none;
content-zooming: none;
}
body {
position: absolute;
margin: 0;
padding: 0;
width: 100%;
height: 100%;
background: #fff;
}
#canvas {
position: absolute;
left: 50%;
top: 50%;
width: 600px;
height: 400px;
margin-left: -300px;
margin-top: -200px;
background: #fff;
}
#frame {
position: absolute;
left: 50%;
top: 50%;
width: 700px;
height: 500px;
margin-left: -350px;
margin-top: -250px;
border-radius: 10px;
box-shadow: 0px 0px 100px 0px #fda;
}
JavaScript:
! function () {
"use strict";
function chromaKey(source, id) {
// create new image
var imgSource = new Image();
//imgSource.crossOrigin = "Anonymous"; Not sure if this should be commented out or not, but I think it should.
imgSource.src = source;
imgSource.onload = function () {
// render image in canvas
var jpg = document.createElement('canvas');
var w = jpg.width = this.width;
var h = jpg.height = this.height;
var ctx = jpg.getContext('2d');
ctx.drawImage(this, 0, 0, w, h);
// chroma Key
var img = ctx.getImageData(0, 0, w, h),
data = img.data;
for (var i =0, n = data.length; i < n; i += 4) {
var r = data [i + 0];
var g = data [i + 1];
var b = data [i + 2];
// make white transparent (rgb > 240, 240, 240)
//if (r > 240 && g > 240 && b > 240) {
// data[i + 3] = 0;
//}
}
// create new transparent image
var transparent = document.createElement('canvas');
transparent.width = w;
transparent.height = h;
var ctx = transparent.getContext('2d');
ctx.putImageData(img, 0, 0);
images[id] = transparent;
}
}
// draw parallax image
function parallax (id, x, y) {
var image = images[id];
if (image) {
ctx.drawImage(image, x, y);
}
}
// main loop
function run() {
// request next frame
requestAnimationFrame(run);
// clear screen
ctx.clearRect(0, 0, canvas.width, canvas.height);
// ease pointer
pointer.cx += (pointer.x - pointer.cx) / 10;
pointer.cy += (pointer.y - pointer.cy) / 10;
var rx = -((canvas.width / 2) - Math.max(15, Math.min(pointer.cx, canvas.width - 15))) / 7;
var ry = -((canvas.height / 2) - Math.max(0, Math.min(pointer.cy, canvas.height - 5))) / 4.75;
// parallax
parallax(0, -20 + (rx / 2), -80 + (ry * 2));
parallax(1, -40 + (rx / 2), 20 + (ry / 2));
parallax(2, -20 + (rx / 3), 90 + (ry / 3));
parallax(3, -20 - (rx / 2), 130 - (ry / 2));
parallax(4, 0 - (rx / 1), 160 - (ry / 1));
parallax(5, 240 - (rx * 2), 220 - (ry * 2));
}
// canvas
var canvas = ge1doot.canvas("canvas"); //I think this might have something to do with it? Not sure.
var ctx = canvas.ctx;
// pointer
var pointer = canvas.pointer;
pointer.cx = pointer.x = canvas.width / 2;
pointer.cy = 0;
pointer.y = canvas.height;
// images
var images = [];
// make jpg images transparent images
chromaKey("pengyu.jpg", 0);
chromaKey("pengyu.jpg", 1);
chromaKey("pengyu.jpg", 2);
chromaKey("pengyu.jpg", 3);
chromaKey("pengyu.jpg", 4);
chromaKey("pengyu.jpg", 5);
// zyva!
run();
}();
最佳答案
关于这段引起问题的代码，您是对的。
var canvas = ge1doot.canvas("canvas");
如果你打开code pen你会看到有一个javascript文件正在被code pen导入
https://s3-us-west-2.amazonaws.com/s.cdpn.io/222599/canvas-pointer.js?v=20150516
确保你导入它们
<script type="text/javascript" src="https://s3-us-west-2.amazonaws.com/s.cdpn.io/222599/canvas-pointer.js?v=20150516"></script>
关于javascript - 实现 ge1doot 的视差代码笔，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/49422987/