CanvasRenderingContext2D.scale()

CanvasRenderingContext2D.scale() 是 Canvas 2D API 根据 x 水平方向和 y 垂直方向,为canvas 单位添加缩放变换的方法。

默认的, 在 canvas 中一个单位实际上就是一个像素。例如,如果我们将0.5作为缩放因子,最终的单位会变成0.5像素,并且形状的尺寸会变成原来的一半。相似的方式,我们将2.0作为缩放因子,将会增大单位尺寸变成两个像素。形状的尺寸将会变成原来的两倍。

语法

void ctx.scale(x, y);

参数

x
水平方向的缩放因子。A negative value flips pixels across the vertical axis. A value of 1 results in no horizontal scaling.
y
垂直方向的缩放因子。A negative value flips pixels across the horizontal axis. A value of 1 results in no vertical scaling.

示例

使用 scale 方法

这是一段使用 scale 方法的简单的代码片段。

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);

结果

The scaled rectangle is red, and the non-scaled rectangle is gray.

使用 scale 水平或竖直翻转

你可以使用 ctx.scale(-1, 1) 水平翻转上下文,使用 ctx.scale(1, -1) 垂直翻转上下文。在这个例子中,"Hello world!" 被水平翻转。

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

规范描述

Specification Status Comment
HTML Living Standard
CanvasRenderingContext2D.scale
Living Standard

浏览器兼容性

BCD tables only load in the browser

参见