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Сообщение от provigator
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не задается прозрачность
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Я попробовал у себя на сервере - пример рабочий.
<!DOCTYPE html>
<html>
<head>
<script type="text/javascript">
//Global variables
var picWidth = 200; // width of the canvas
var picHeight = 200; // height of the canvas
var picLength = picWidth * picHeight; // number of chunks
var myImage = new Image(); // Create a new blank image.
// Load the image and display it.
function displayImage() {
// Get the canvas element.
canvas = document.getElementById("myCanvas");
// Make sure you got it.
if (canvas.getContext) {
// Specify 2d canvas type.
ctx = canvas.getContext("2d");
// When the image is loaded, draw it.
myImage.onload = function() {
// Load the image into the context.
ctx.drawImage(myImage, 0, 0);
// Get and modify the image data.
getColorData();
// Put the modified image back on the canvas.
putColorData();
}
// Define the source of the image.
// This file must be on your machine in the same folder as this web page.
myImage.src = "img/test.png";
}
}
function getColorData() {
myImage = ctx.getImageData(0, 0, 200, 200);
// Loop through data.
for (var i = 0; i < picLength * 4; i += 4) {
// First bytes are red bytes.
// Second bytes are green bytes.
// Third bytes are blue bytes.
// Fourth bytes are alpha bytes
// Test of alpha channel at 50%.
myImage.data[i + 3] = 128;
}
}
function putColorData() {
ctx.putImageData(myImage, 0, 0);
}
function noPhoto() {
alert("Please put a .png file in this folder and name it kestral.png.");
}
</script>
</head>
<body onload="displayImage()">
<h1>
American Kestral
</h1>
<p>
The original image is on the left and the modified image is on the right.
</p>
<img id="myPhoto" src="img/test.png" onerror="noPhoto()">
<canvas id="myCanvas" width="200" height="200">
</canvas>
<p>
Public domain image courtesy of U.S. Fish and Wildlife Service.
</p>
</body>
</html>