OffscreenCanvasRenderingContext2D对象


OffscreenCanvasRenderingContext2D对象

说明: 从API version 7开始支持。后续版本如有新增内容,则采用上角标单独标记该内容的起始版本。

使用OffscreenCanvasRenderingContext2D在offscreen canvas上进行绘制,绘制对象可以是矩形、文本、图片等

属性

除支持与CanvasRenderingContext2D对象相同的属性外,还支持如下属性:

属性 类型 描述
filter string 设置图像的滤镜。
支持的滤镜效果如下:
- blur:给图像设置高斯模糊
- brightness:给图片应用一种线性乘法,使其看起来更亮或更暗
- contrast:调整图像的对比度
- drop-shadow:给图像设置一个阴影效果
- grayscale:将图像转换为灰度图像
- hue-rotate:给图像应用色相旋转
- invert:反转输入图像
- opacity:转化图像的透明程度
- saturate:转换图像饱和度
- sepia:将图像转换为深褐色

示例:

<!-- xxx.hml -->
<div style="width: 500px; height: 500px;">
  <canvas ref="canvasId" style="width: 500px; height: 500px; background-color: #ffff00;"></canvas>
</div>
1
2
3
4
// xxx.js
export default {
  onShow(){
    var ctx = this.$refs.canvasId.getContext('2d');
    var offscreen = new OffscreenCanvas(360, 500);
    var offCanvas2 = offscreen.getContext("2d");
    var img = new Image();
    img.src = 'common/images/flower.jpg';
    offCanvas2.drawImage(img, 0, 0, 100, 100);
    offCanvas2.filter = 'blur(5px)';
    offCanvas2.drawImage(img, 100, 0, 100, 100);

    offCanvas2.filter = 'grayscale(50%)';
    offCanvas2.drawImage(img, 200, 0, 100, 100);

    offCanvas2.filter = 'hue-rotate(90deg)';
    offCanvas2.drawImage(img, 0, 100, 100, 100);

    offCanvas2.filter = 'invert(100%)';
    offCanvas2.drawImage(img, 100, 100, 100, 100);

    offCanvas2.filter = 'drop-shadow(8px 8px 10px green)';
    offCanvas2.drawImage(img, 200, 100, 100, 100);

    offCanvas2.filter = 'brightness(0.4)';
    offCanvas2.drawImage(img, 0, 200, 100, 100);

    offCanvas2.filter = 'opacity(25%)';
    offCanvas2.drawImage(img, 100, 200, 100, 100);

    offCanvas2.filter = 'saturate(30%)';
    offCanvas2.drawImage(img, 200, 200, 100, 100);

    offCanvas2.filter = 'sepia(60%)';
    offCanvas2.drawImage(img, 0, 300, 100, 100);

    offCanvas2.filter = 'contrast(200%)';
    offCanvas2.drawImage(img, 100, 300, 100, 100);
    var bitmap = offscreen.transferToImageBitmap();
    ctx.transferFromImageBitmap(bitmap);
  }
}
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42

方法

除支持与CanvasRenderingContext2D对象相同的方法外,还支持如下方法:

isPointInPath

isPointInPath(path?: Path2D, x: number, y: number): boolean

判断指定点是否在路径的区域内。

参数:

参数名 参数类型 必填 描述
path Path2D 可选对象,指定用来判断的路径。若没有设置,则使用当前路径。
x number 待判断点的x轴坐标。
y number 待判断点的y轴坐标。

返回值:

类型 说明
boolean 指定点是否在路径的区域内。

示例:

<!-- xxx.hml -->
<div style="width: 500px; height: 500px;">
  <text>In path:{{textValue}}</text>
  <canvas ref="canvas" style="width: 500px; height: 500px; background-color: #ffff00;"></canvas>
</div>
1
2
3
4
5
// xxx.js
export default {
  data: {
    textValue: 0
  },
  onShow(){
    var canvas = this.$refs.canvas.getContext('2d');
    var offscreen = new OffscreenCanvas(500,500);
    var offscreenCanvasCtx = offscreen.getContext("2d");

    offscreenCanvasCtx.rect(10, 10, 100, 100);
    offscreenCanvasCtx.fill();
    this.textValue = offscreenCanvasCtx.isPointInPath(30, 70);

    var bitmap = offscreen.transferToImageBitmap();
    canvas.transferFromImageBitmap(bitmap);
  }
}
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18

zh-cn_image_0000001224354967

isPointInStroke

isPointInStroke(path?: Path2D, x: number, y: number): boolean

判断指定点是否在路径的边缘线上。

参数:

参数名 参数类型 必填 描述
path Path2D 可选对象,指定用来判断的路径。若没有设置,则使用当前路径。
x number 待判断点的x轴坐标。
y number 待判断点的y轴坐标。

返回值:

类型 说明
boolean 指定点是否在路径的区域内。

示例:

<!-- xxx.hml -->
<div style="width: 500px; height: 500px;">
  <text>In path:{{textValue}}</text>
  <canvas ref="canvas" style="width: 500px; height: 500px; background-color: #ffff00;"></canvas>
</div>
1
2
3
4
5
// xxx.js
export default {
  data: {
    textValue: 0
  },
  onShow(){
    var canvas = this.$refs.canvas.getContext('2d');
    var offscreen = new OffscreenCanvas(500,500);
    var offscreenCanvasCtx = offscreen.getContext("2d");

    offscreenCanvasCtx.rect(10, 10, 100, 100);
    offscreenCanvasCtx.stroke();
    this.textValue = offscreenCanvasCtx.isPointInStroke(50, 10);

    var bitmap = offscreen.transferToImageBitmap();
    canvas.transferFromImageBitmap(bitmap);
  }
}
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18

zh-cn_image_0000001178875308

resetTransform

resetTransform(): void

示例:

<!-- xxx.hml -->
<div style="width: 500px; height: 500px;">
  <text>In path:{{textValue}}</text>
  <canvas ref="canvas" style="width: 500px; height: 500px; background-color: #ffff00;"></canvas>
</div>
1
2
3
4
5
// xxx.js
export default {
  data:{
   textValue:0
  },
  onShow(){
   var canvas = this.$refs.canvas.getContext('2d');
   var offscreen = new OffscreenCanvas(500,500);
   var offscreenCanvasCtx = offscreen.getContext("2d");

   offscreenCanvasCtx.transform(1, 0, 1.7, 1, 0, 0);
   offscreenCanvasCtx.fillStyle = 'gray';
   offscreenCanvasCtx.fillRect(40, 40, 50, 20);
   offscreenCanvasCtx.fillRect(40, 90, 50, 20);

   // Non-skewed rectangles
   offscreenCanvasCtx.resetTransform();
   offscreenCanvasCtx.fillStyle = 'red';
   offscreenCanvasCtx.fillRect(40, 40, 50, 20);
   offscreenCanvasCtx.fillRect(40, 90, 50, 20);

   var bitmap = offscreen.transferToImageBitmap();
   canvas.transferFromImageBitmap(bitmap);
  } 
}
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25

zh-cn_image_0000001179035242