JavaScript canvas2d object property: globalCompositeOperation
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The globalCompositeOperation property of
the JavaScript
DOM object returned
by the getContext("2d")
method applied to the HTML <canvas>
element sets / returns how new images are drawn onto existing images.
It can take the following
values:
|
Value
|
Meaning
|
|
copy
|
Source image only
(destination image is ignored)
|
|
destination-atop
|
As per source-atop but
with source and destination flipped
|
|
destination-in
|
As per source-in but
with source and destination flipped
|
|
destination-out
|
As per source-out but
with source and destination flipped
|
|
destination-over
|
As per source-over but
with source and destination flipped
|
|
lighter
|
Source image +
destination image
|
|
source-atop
|
Source image on top of
destination image (part of source image outside destination image is ignored)
|
|
source-in
|
Source image into
destination image (only part of source image inside destination image is
shown, destination image is transparent)
|
|
source-out
|
Source image out of
destination image (only part of source image outside destination image is
shown, destination image is transparent)
|
|
source-over
|
(default). Source image
over destination image
|
|
xor
|
Source and destination
images combined using XOR operation
|
EXAMPLE:
HTML USED IN THIS EXAMPLE:
<!DOCTYPE html>
<html> <!-- Copyright (c) Nematrian Limited 2018 -->
<head></head>
<body>
<span id="element"></span>
<script>
var x2 = document.createElement("CANVAS");
x2.setAttribute("width", "200");
x2.setAttribute("height", "100");
x2.setAttribute("style", "border: 1px solid black");
var c2 = x2.getContext("2d");
c2.fillStyle = "blue";
c2.fillRect(10, 10, 50, 60);
c2.fillStyle = "orange";
c2.fillRect(30, 30, 50, 60);
c2.fillStyle = "blue";
c2.fillRect(110, 10, 50, 60);
c2.fillStyle = "orange";
c2.globalCompositeOperation="lighter";
c2.fillRect(130, 30, 50, 60);
document.getElementById("element").appendChild(x2);
</script>
</body>
</html>
|
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