The CanvasRenderingContext2D
.globalCompositeOperation
property of the Canvas 2D API sets the type of compositing operation to apply when drawing new shapes, where type is a string identifying which of the compositing or blending mode operations to use.
See also the chapter Compositing in the Canvas Tutorial.
Syntax
ctx.globalCompositeOperation = type;
Types
Examples
Using the globalCompositeOperation
property
This is just a simple code snippet using the globalCompositeOperation
property to draw two rectangles that exclude themselves where they overlap.
HTML
<canvas id="canvas"></canvas>
JavaScript
var canvas = document.getElementById("canvas");
var ctx = canvas.getContext("2d");
ctx.globalCompositeOperation = "xor";
ctx.fillStyle = "blue";
ctx.fillRect(10, 10, 100, 100);
ctx.fillStyle = "red";
ctx.fillRect(50, 50, 100, 100);
Edit the code below and see your changes update live in the canvas:
Playable code
<canvas id="canvas" width="400" height="200" class="playable-canvas"></canvas>
<div class="playable-buttons">
<input id="edit" type="button" value="Edit" />
<input id="reset" type="button" value="Reset" />
</div>
<textarea id="code" class="playable-code" style="height:120px;">
ctx.globalCompositeOperation = "xor";
ctx.fillStyle = "blue";
ctx.fillRect(10, 10, 100, 100);
ctx.fillStyle = "red";
ctx.fillRect(50, 50, 100, 100);</textarea>
var canvas = document.getElementById("canvas");
var ctx = canvas.getContext("2d");
var textarea = document.getElementById("code");
var reset = document.getElementById("reset");
var edit = document.getElementById("edit");
var code = textarea.value;
function drawCanvas() {
ctx.clearRect(0, 0, canvas.width, canvas.height);
eval(textarea.value);
}
reset.addEventListener("click", function() {
textarea.value = code;
drawCanvas();
});
edit.addEventListener("click", function() {
textarea.focus();
})
textarea.addEventListener("input", drawCanvas);
window.addEventListener("load", drawCanvas);
Specifications
Specification | Status | Comment |
---|---|---|
WHATWG HTML Living Standard The definition of 'CanvasRenderingContext2D.globalCompositeOperation' in that specification. |
Living Standard | |
Compositing and blending Level 1 | Candidate Recommendation |
Browser compatibility
Feature | Chrome | Firefox (Gecko) | Internet Explorer | Opera | Safari |
---|---|---|---|---|---|
Basic support | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) |
Blend modes | ? | 20 (20) | ? | ? | ? |
WebKit/Blink-specific notes
- In WebKit- and Blink-based Browsers, a non-standard and deprecated method
ctx.setCompositeOperation()
is implemented besides this property. - Support for "plus-darker" and "darker" were removed in Chrome 48. Developers looking a replacement should use "darken".
Gecko-specific notes
- An early Canvas specification draft specified the value "darker". However, Firefox removed support for "darker" in version 4 (bug 571532). See also this blog post that suggests to use the
difference
value to achieve a similar affect to "darker".
See also
- The interface defining it,
CanvasRenderingContext2D
CanvasRenderingContext2D.globalAlpha