js-offscreencanvasrenderingcontext2d.md

# OffscreenCanvasRenderingContext2D

>  **NOTE**
>
>  The APIs of this module are supported since API version 7. Updates will be marked with a superscript to indicate their earliest API version.


Use **OffscreenCanvasRenderingContext2D** to draw rectangles, images, and texts on an **OffscreenCanvas**.


## Attributes

In addition to the attributes that are supported by **CanvasRenderingContext2D**, the following attributes are supported.

| Name    | Type    | Description                                      |
| ------ | ------ | ---------------------------------------- |
| filter | string | Image filter.<br>Available options are as follows:<br>- **blur**: applies the Gaussian blur for the image.<br>- **brightness**: applies a linear multiplication to the image to make it look brighter or darker.<br>- **contrast**: adjusts the image contrast.<br>- **drop-shadow**: sets a shadow effect for the image.<br>- **grayscale**: converts the image to a grayscale image.<br>- **hue-rotate**: applies hue rotation to the image.<br>- **invert**: inverts the input image.<br>- **opacity**: sets the opacity of the image.<br>- **saturate**: sets the saturation of the image.<br>- **sepia**: converts the image to dark brown. |

**Example**
```html
<!-- xxx.hml -->
<div style="width: 180px; height: 60px;">
  <canvas ref="canvasId" style="width: 500px; height: 500px; background-color: #ffff00;"></canvas>
</div>
```

```js
// 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);
  }
}
```

## Methods

In addition to the methods that are supported by **CanvasRenderingContext2D**, the following methods are supported.


### isPointInPath

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

Checks whether a specified point is in the path area.

**Parameters**
| Name | Type  | Mandatory  | Description                           |
| ---- | ------ | ---- | ----------------------------- |
| path | Path2D | No   | Path used for checking. If this parameter is not set, the current path is used.|
| x    | number | Yes   | X-coordinate of the point used for checking.                   |
| y    | number | Yes   | Y-coordinate of the point used for checking.                   |

**Return value**
| Type     | Description           |
| ------- | ------------- |
| boolean | Whether a specified point is in the path area.|

**Example**
```html
<!-- xxx.hml -->
<div style="width: 180px; height: 60px;">
  <text>In path:{{textValue}}</text>
  <canvas ref="canvas" style="width: 500px; height: 500px; background-color: #ffff00;"></canvas>
</div>
```

```js
// 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);
  }
}
```

![en-us_image_0000001224354967](figures/en-us_image_0000001224354967.png)

### isPointInStroke

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

Checks whether a specified point is on the edge line of a path.

**Parameters**
| Name | Type  | Mandatory  | Description                           |
| ---- | ------ | ---- | ----------------------------- |
| path | Path2D | No   | Path used for checking. If this parameter is not set, the current path is used.|
| x    | number | Yes   | X-coordinate of the point used for checking.                   |
| y    | number | Yes   | Y-coordinate of the point used for checking.                   |

**Return value**
| Type     | Description           |
| ------- | ------------- |
| boolean | Whether a specified point is in the path area.|

**Example**
```html
<!-- xxx.hml -->
<div style="width: 180px; height: 60px;">
  <text>In path:{{textValue}}</text>
  <canvas ref="canvas" style="width: 500px; height: 500px; background-color: #ffff00;"></canvas>
</div>
```

```js
// 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);
  }
}
```

![en-us_image_0000001178875308](figures/en-us_image_0000001178875308.png)

### resetTransform

resetTransform(): void

**Example**
```html
<!-- xxx.hml -->
<div style="width: 180px; height: 60px;">
  <text>In path:{{textValue}}</text>
  <canvas ref="canvas" style="width: 500px; height: 500px; background-color: #ffff00;"></canvas>
</div>
```

```js
// 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);
  } 
}
```

![en-us_image_0000001179035242](figures/en-us_image_0000001179035242.png)