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);
结果
规范
Specification |
---|
HTML Standard # dom-context-2d-scale-dev |
浏览器兼容性
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