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：

示例：

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

// 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);
  }
}

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：

返回值：

示例：

<!-- xxx.hml -->
<div class="container" style="width: 500px; height: 500px;">
    <text class="textsize">In path:{{textValue}}</text>
    <canvas ref="canvas" style="width: 500px; height: 500px; background-color: #ffff00;"></canvas>
</div>

/* xxx.css */
.container {
    display: flex;
    flex-direction: column;
    background-color: #F1F3F5;
    align-items: center;
    justify-content: center;
    width: 100%;
    height: 100%;
}

canvas {
    width: 600px;
    height: 600px;
    background-color: #fdfdfd;
    border: none;
}

.textsize {
    font-size: 40px;
}

// 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);
  }
}

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：

返回值：

示例：

<!-- xxx.hml -->
<div class="container" style="width: 500px; height: 500px;">
    <text class="textsize">In stroke:{{textValue}}</text>
    <canvas ref="canvas" style="width: 500px; height: 500px; background-color: #ffff00;"></canvas>
</div>

/* xxx.css */
.container {
    display: flex;
    flex-direction: column;
    background-color: #F1F3F5;
    align-items: center;
    justify-content: center;
    width: 100%;
    height: 100%;
}

canvas {
    width: 600px;
    height: 600px;
    background-color: #fdfdfd;
    border: none;
}

.textsize {
    font-size: 40px;
}

// 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);
  }
}

resetTransform

resetTransform(): void

示例：

<!-- xxx.hml -->
<div class="container" style="width: 500px; height: 500px;">
    <text class="textsize">In path:{{textValue}}</text>
    <canvas ref="canvas" style="width: 500px; height: 500px; background-color: #ffff00;"></canvas>
</div>

/* xxx.css */
.container {
    display: flex;
    flex-direction: column;
    background-color: #F1F3F5;
    align-items: center;
    justify-content: center;
    width: 100%;
    height: 100%;
}

canvas {
    width: 600px;
    height: 600px;
    background-color: #fdfdfd;
    border: none;
}

.textsize {
    font-size: 40px;
}

// 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 = '#a9a9a9';
   offscreenCanvasCtx.fillRect(40, 40, 50, 20);
   offscreenCanvasCtx.fillRect(40, 90, 50, 20);

   // Non-skewed rectangles
   offscreenCanvasCtx.resetTransform();
   offscreenCanvasCtx.fillStyle = '#ff0000';
   offscreenCanvasCtx.fillRect(40, 40, 50, 20);
   offscreenCanvasCtx.fillRect(40, 90, 50, 20);

   var bitmap = offscreen.transferToImageBitmap();
   canvas.transferFromImageBitmap(bitmap);
  } 
}