OffscreenCanvasRenderingContext2D对象

说明： 从API Version 7 开始支持。

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
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/example.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：

名称

参数

描述

isPointInPath

path?: Path2D, x: number, y: number

判断指定点是否在路径的区域内。

path：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：待判断点的x轴坐标

y：待判断点的y轴坐标

isPointInStroke

path?: Path2D, x: number, y: number

判断指定点是否在路径的边缘线上。

path：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：待判断点的x轴坐标

y：待判断点的y轴坐标

resetTransform

无

将当前变换重置为单位矩阵。

  • isPointInPath示例

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

    // 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示例

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

    // 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示例

    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);