canvas-image animation catalog
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Preface
canvasImage animation effects mentioned in the development manual
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Code display
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Document</title>
<style>
body {
background-color: rgba(100, 145, 250, 0.3);
}
#canvas {
margin-left: 20px;
margin-right: 0px;
margin-bottom: 20px;
border: thin solid #aaffcc;
cursor: crosshair;
padding: 0;
}
#controls {
margin: 20px;
}
a {
font: 18px Times Roman;
text-decoration: none;
margin-right: 15px;
}
</style>
</head>
<body>
<div id="controls">
<input type="button" id="fadeButton" value="Fade Out">
</div>
<canvas id="canvas" width="800" height="520">
Canvas Not Supported!
</canvas>
<script src="main.js"></script>
</body>
</html>
// main.js
var image = new Image(),
canvas = document.getElementById('canvas'),
context = canvas.getContext('2d'),
fadeButton = document.getElementById('fadeButton'),
originalImageData = null,
interval = null;
// Functions.....................................................
function increaseTransparency(imagedata, steps) {
var alpha, currentAlpha, step, length = imagedata.data.length;
for (var i=3; i < length; i+=4) {
// For every alpha component
alpha = originalImageData.data[i];
if (alpha > 0 && imagedata.data[i] > 0) {
// not totally transparent yet
currentAlpha = imagedata.data[i];
step = Math.ceil(alpha/steps);
if (currentAlpha - step > 0) {
// not too close to the end
imagedata.data[i] -= step; // increase transparency
}
else {
imagedata.data[i] = 0; // end: totally transparent
}
}
}
}
function fadeOut(context, imagedata, x, y,
steps, millisecondsPerStep) {
var frame = 0,
length = imagedata.data.length;
interval = setInterval(function () {
// Once every millisecondsPerStep ms
frame++;
if (frame > steps) {
// animation is over
clearInterval(interval); // end animation
animationComplete(); // put picture back in 1s
}
else {
increaseTransparency(imagedata, steps);
context.putImageData(imagedata, x, y);
}
}, millisecondsPerStep);
};
// Animation.....................................................
function animationComplete() {
setTimeout(function() {
context.drawImage(image,0,0,canvas.width,canvas.height);
}, 1000);
}
// Initialization................................................
fadeButton.onclick = function() {
fadeOut(context,
context.getImageData(0, 0, canvas.width, canvas.height),
0, 0, 20, 1000/60);
};
image.src = './log-crossing.png';
image.onload = function() {
context.drawImage(image, 0, 0, canvas.width, canvas.height);
originalImageData = context.getImageData(0, 0, canvas.width, canvas.height);
};