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web api instance method

CanvasRenderingContext2D: scale() method

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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

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

<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).

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.

Interactive exampleOpen the canonical MDN source to run this embedded demo.

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

<canvas id="canvas"></canvas>

JavaScript

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

Interactive exampleOpen the canonical MDN source to run this embedded demo.

Specifications

SpecificationsStandards references are available on the canonical MDN page.

Browser compatibility

Browser compatibilityCompatibility data is available on the canonical MDN page.

See also