CanvasRenderingContext2D: scale() method
The
CanvasRenderingContext2D.scale()
method of the Canvas 2D API adds a scaling transformation to the canvas units
horizontally and/or vertically.
By default, one unit on the canvas is exactly one pixel. A scaling transformation modifies this behavior. For instance, a scaling factor of 0.5 results in a unit size of 0.5 pixels; shapes are thus drawn at half the normal size. Similarly, a scaling factor of 2.0 increases the unit size so that one unit becomes two pixels; shapes are thus drawn at twice the normal size.
Syntax
js
scale(x, y)
Parameters
x
-
Scaling factor in the horizontal direction. A negative value flips pixels across the vertical axis. A value of
1
results in no horizontal scaling. y
-
Scaling factor in the vertical direction. A negative value flips pixels across the horizontal axis. A value of
1
results in no vertical scaling.
Return value
None (undefined
).
Examples
Scaling a shape
This example draws a scaled rectangle. A non-scaled rectangle is then drawn for comparison.
HTML
html
<canvas id="canvas"></canvas>
JavaScript
The rectangle has a specified width of 8 and a height of 20. The transformation matrix scales it by 9x horizontally and by 3x vertically. Thus, its final size is a width of 72 and a height of 60.
Notice that its position on the canvas also changes. Since its specified corner is (10, 10), its rendered corner becomes (90, 30).
js
const canvas = document.getElementById("canvas");
const ctx = canvas.getContext("2d");
// Scaled rectangle
ctx.scale(9, 3);
ctx.fillStyle = "red";
ctx.fillRect(10, 10, 8, 20);
// Reset current transformation matrix to the identity matrix
ctx.setTransform(1, 0, 0, 1, 0, 0);
// Non-scaled rectangle
ctx.fillStyle = "gray";
ctx.fillRect(10, 10, 8, 20);
Result
The scaled rectangle is red, and the non-scaled rectangle is gray.
Flipping things horizontally or vertically
You can use scale(-1, 1)
to flip the context horizontally and
scale(1, -1)
to flip it vertically. In this example, the words "Hello
world!" are flipped horizontally.
Note that the call to fillText()
specifies a negative x coordinate. This is to adjust for the negative scaling factor:
-280 * -1
becomes 280
, and text is drawn leftwards from that
point.
HTML
html
<canvas id="canvas"></canvas>
JavaScript
js
const canvas = document.getElementById("canvas");
const ctx = canvas.getContext("2d");
ctx.scale(-1, 1);
ctx.font = "48px serif";
ctx.fillText("Hello world!", -280, 90);
ctx.setTransform(1, 0, 0, 1, 0, 0);
Result
Specifications
Specification |
---|
HTML Standard # dom-context-2d-scale-dev |
Browser compatibility
BCD tables only load in the browser
See also
- The interface defining this method:
CanvasRenderingContext2D