HarmonyOS Developer Canvas开发指导

丶龙八夷

发布于 2023-3-27 17:08

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Canvas对象

Canvas组件提供画布，用于自定义绘制图形。具体用法请参考CanvasRenderingContext2D对象。

创建Canvas组件

在pages/index目录下的hml文件中创建一个Canvas组件。

<!-- xxx.hml -->
<div class="container">
  <canvas></canvas>
</div>

/* xxx.css */
.container{
  width: 100%;
  height: 100%;
  flex-direction: column;
  justify-content: center;
  align-items: center;
  background-color: #F1F3F5;
}
canvas{
  background-color: #00ff73;
}

HarmonyOS Developer Canvas开发指导-鸿蒙开发者社区

说明

Canvas组件默认背景色与父组件的背景色一致。
Canvas默认宽高为width: 300px，height: 150px。

添加样式

Canvas组件设置宽（width）、高（height）、背景色（background-color）及边框样式（border）。

<!-- xxx.hml -->
<div class="container">
  <canvas></canvas>
</div>

/* xxx.css */
.container{
  flex-direction: column;
  justify-content: center;
  align-items: center;
  background-color: #F1F3F5;
  width: 100%;
  height: 100%;
}
canvas{
  width: 500px;
  height: 500px;  
  background-color: #fdfdfd;  
  border: 5px solid red;
}

HarmonyOS Developer Canvas开发指导-鸿蒙开发者社区

添加事件

Canvas添加长按事件，长按后可获取Canvas组件的dataUrl值（toDataURL方法返回的图片信息），打印在下方文本区域内。

<!-- xxx.hml -->
<div class="container">
  <canvas ref="canvas1" onlongpress="getUrl"></canvas>
  <text>dataURL</text>
  <text class="content">{{dataURL}}</text>
</div>

/* xxx.css */
.container{
  width:100%;
  height:100%;
  flex-direction: column;
  justify-content: center;
  align-items: center;
  background-color: #F1F3F5;
  }
  canvas{  
    width: 500px;  
    height: 500px;
    background-color: #fdfdfd;
    border: 5px solid red;
    margin-bottom: 50px;
}
.content{
  border: 5px solid blue;
  padding: 10px;
  width: 90%;
  height: 400px; 
  overflow: scroll;
}

// xxx.js
import promptAction from '@ohos.promptAction';
export default {
  data:{
    dataURL:null,
  },
  onShow(){
    let el = this.$refs.canvas1;
    let ctx = el.getContext("2d"); 
    ctx.strokeRect(100,100,300,300);
  },
  getUrl(){
    let el = this.$refs.canvas1
    let dataUrl = el.toDataURL()
    this.dataURL = dataUrl;
    promptAction.showToast({duration:2000,message:"long press,get dataURL"})
  }
}

HarmonyOS Developer Canvas开发指导-鸿蒙开发者社区

说明

画布不支持在onInit和onReady中进行创建。

CanvasRenderingContext2D对象

使用CanvasRenderingContext2D在Canvas画布组件上进行绘制，绘制对象可以是图形、文本、线段、图片等。具体请参考CanvasRenderingContext2D对象。

画线段

使用moveTo和lineTo画出一条线段，当使用closePath方法时会结束当前路径形成一个封闭图形。设置quadraticCurveTo（二次贝赛尔曲线）或bezierCurveTo（三次贝赛尔曲线）的值组成图形。

<!-- xxx.hml -->
<div class="container">
  <canvas ref="canvas1"></canvas>
  <select @change="change">
    <option value="value1"> line </option>
    <option value="value2"> quadratic </option>
    <option value="value3"> bezier </option>
    <option value="value4"> arc/ellipse </option>
    <option value="value5"> lineJoin/miterLimit </option>
  </select>
</div>

/* xxx.css */
.container{
  width: 100%;
  height: 100%;
  flex-direction: column;
  justify-content: center;
  align-items: center;
  background-color: #F1F3F5;
}
canvas{
  width: 600px;
  height: 500px;
  background-color: #fdfdfd;
  border: 5px solid red;
}
select{
  margin-top: 50px;
  width: 250px;
  height: 100px;
  background-color: white;
}

// xxx.js
export default {
  data:{
    el: null,
    ctx: null,
  },
  onShow(){
    this.el = this.$refs.canvas1;
    this.ctx = this.el.getContext("2d",{antialias: true});
    // 清除画布上的内容
    this.ctx.clearRect(0, 0, 600, 500);
    // 创建一个新的绘制路径
    this.ctx.beginPath();
    // 线端点以方形结束
    this.ctx.lineCap = 'butt';
    // 描边的宽度
    this.ctx.lineWidth = 15;
    // 创建一个新的绘制路径
    this.ctx.beginPath();
    // 路径从当前点移动到指定点
    this.ctx.moveTo(200, 100);
    // 从当前点到指定点进行路径连接
    this.ctx.lineTo(400, 100);
    // 边框绘制
    this.ctx.stroke();
    this.ctx.beginPath();
    // 线端点以圆形结束
    this.ctx.lineCap = 'round';
    this.ctx.moveTo(200, 200);
    this.ctx.lineTo(400, 200);
    this.ctx.stroke();
    // 线端点以方形结束
    this.ctx.beginPath();
    this.ctx.lineCap = 'square';
    this.ctx.moveTo(200, 300);
    this.ctx.lineTo(400, 300);
    this.ctx.stroke();
  },
  change(e){
    if(e.newValue == 'value1'){
      this.el = this.$refs.canvas1;
      this.ctx = this.el.getContext("2d",{antialias: true});
      this.ctx.clearRect(0, 0, 600, 500);
      // 上
      this.ctx.beginPath();
      this.ctx.lineCap = 'butt';
      this.ctx.moveTo(200, 100);
      this.ctx.lineTo(400, 100);
      this.ctx.stroke();
      // 中
      this.ctx.beginPath();
      this.ctx.lineCap = 'round';
      this.ctx.moveTo(200, 200);
      this.ctx.lineTo(400, 200);
      this.ctx.stroke();
      // 下
      this.ctx.beginPath();
      this.ctx.lineCap = 'square';
      this.ctx.moveTo(200, 300);
      this.ctx.lineTo(400, 300);
      this.ctx.stroke();
    }else if(e.newValue == 'value2'){
      this.ctx.clearRect(0, 0, 600, 500);
      // 上
      this.ctx.beginPath();
      this.ctx.moveTo(100, 150);
      // 二次贝赛尔曲线的路径
      this.ctx.quadraticCurveTo(300, 50, 500, 150);
      this.ctx.stroke();
      // 左
      this.ctx.beginPath();
      this.ctx.moveTo(200, 150);
      this.ctx.quadraticCurveTo(250, 250, 250, 400);
      this.ctx.stroke();
      // 右
      this.ctx.beginPath();
      this.ctx.moveTo(400, 150);
      this.ctx.quadraticCurveTo(350, 250, 350, 400);
      this.ctx.stroke();
    }else if(e.newValue == 'value3'){
      this.ctx.clearRect(0, 0, 600, 500);
      // 下
      this.ctx.beginPath();
      this.ctx.moveTo(100, 200);
      // 三次贝赛尔曲线的路径
      this.ctx.bezierCurveTo(150, 100, 200, 100,250, 200);
      this.ctx.stroke();
      // 左
      this.ctx.beginPath();
      this.ctx.moveTo(350, 200);
      this.ctx.bezierCurveTo(400, 100, 450, 100,500, 200);
      this.ctx.stroke();
      // 右
      this.ctx.beginPath();
      this.ctx.moveTo(200, 350);
      this.ctx.bezierCurveTo(250, 500, 350, 500, 400, 350);
      this.ctx.stroke();
    }else if(e.newValue == 'value4'){
      this.ctx.clearRect(0, 0, 600, 500);
      this.ctx.beginPath();
      this.ctx.moveTo(100, 200);
      // 弧线
      this.ctx.arcTo(150, 300, 350, 300, 150);
      this.ctx.stroke();
      this.ctx.beginPath();
      // 椭圆
      this.ctx.ellipse(400, 250, 50, 100, Math.PI * 0.25, Math.PI * 0.5 , Math.PI , 1);
      this.ctx.stroke();
    }else if(e.newValue == 'value5'){
      this.ctx.clearRect(0, 0, 600, 500);
      // 左上
      this.ctx.beginPath();
      // 在线段相连处绘制一个扇形
      this.ctx.lineJoin = 'round';
      this.ctx.moveTo(100, 100);
      this.ctx.lineTo(200, 200);
      this.ctx.lineTo(100, 250);
      this.ctx.stroke();
      // 左下
      this.ctx.beginPath();
      // 在线段相连处使用三角形为底填充
      this.ctx.lineJoin = 'bevel';
      this.ctx.moveTo(100, 300);
      this.ctx.lineTo(200, 400);
      this.ctx.lineTo(100, 450);
      this.ctx.stroke();
      // 右上
      this.ctx.beginPath();
      //线条相交处内角和外角的距离
      this.ctx.lineJoin = 'miter';
      this.ctx.miterLimit = 3;
      this.ctx.moveTo(400, 100);
      this.ctx.lineTo(450, 200);
      this.ctx.lineTo(400, 250);
      // 结束当前路径形成一个封闭路径
      this.ctx.closePath();
      this.ctx.stroke();
      // 右下
      this.ctx.beginPath();
      this.ctx.lineJoin = 'miter';
      this.ctx.miterLimit = 10;
      this.ctx.moveTo(400, 300);
      this.ctx.lineTo(450, 400);
      this.ctx.lineTo(400, 450);
      this.ctx.closePath();
      this.ctx.stroke();
    }
  },
}

HarmonyOS Developer Canvas开发指导-鸿蒙开发者社区

画边框

全局定义画布（el）及画笔（ctx），初始化创建一个边框宽度为5的长方形。对边框的宽度（lineWidth）、颜色（strokeStyle）、虚化程度（setLineDash）进行改变，选用select组件添加change事件，下拉选择时触发change事件后画出改变后的图形。

<!-- xxx.hml -->
<div class="container">
  <canvas ref="canvas1"></canvas>
  <select @change="change">
    <option value="value1">strokeRect</option>
    <option value="value2">arc</option>
    <option value="value3">lineDashRect</option>
    <option value="value4">fillRect</option>
  </select>
</div>

/* xxx.css */
.container{
  width: 100%;
  height: 100%;
  flex-direction: column;
  justify-content: center;
  align-items: center;
  background-color: #F1F3F5;
}
canvas{
  width: 600px;
  height: 500px;
  background-color: #fdfdfd;
  border: 5px solid red;
}
select{
  margin-top: 50px;
  width: 250px;
  height: 100px;
  background-color: white;
}

// xxx.js
export default {
  data:{
    el: null,
    ctx: null,
  },
  onShow(){
    this.el = this.$refs.canvas1;
    this.ctx = this.el.getContext("2d",{antialias: true});
    this.ctx.lineWidth = 5;
    this.ctx.strokeRect(200, 150, 200, 200);
  },
  change(e){
    if(e.newValue == 'value1'){
      // 清除画布上的内容
      this.ctx.clearRect(0,0,600,500);
      // 边框宽度
      this.ctx.lineWidth = 5;
      // 边框颜色
      this.ctx.strokeStyle = '#110000';
      // 边框的虚化程度
      this.ctx.setLineDash([0,0]);
      // 画具有边框的矩形
      this.ctx.strokeRect(200, 150, 200, 200);
    }else if (e.newValue == 'value2'){
      this.ctx.clearRect(0,0,600,500);
      this.ctx.lineWidth = 30;
      this.ctx.strokeStyle = '#0000ff';
      this.ctx.setLineDash([0,0]);
      // 画圆
      this.ctx.arc(300, 250, 150,0,6.28);
      //进行边框绘制
      this.ctx.stroke();
    }else if (e.newValue == 'value3'){
      this.ctx.clearRect(0,0,600,500);
      this.ctx.lineWidth = 5;
      this.ctx.setLineDash([5,5]);
      this.ctx.strokeRect(200, 150, 200, 200);
    }else if (e.newValue == 'value4'){
      this.ctx.clearRect(0,0,600,500);
      // 画一个有填充颜色的矩形
      this.ctx.fillStyle = '#0000ff';
      this.ctx.fillRect(200, 150, 200, 200);
    }
  },
}

HarmonyOS Developer Canvas开发指导-鸿蒙开发者社区

填充渐变色

添加createLinearGradient和createRadialGradient属性创建渐变容器，接着用addColorStop方法添加多个色块组成渐变色，再设置fillStyle为gradient将渐变色填充到矩形中，最后设置阴影的模糊级别（shadowBlur）、阴影颜色（shadowColor）及阴影偏移量（shadowOffset）。

<!-- xxx.hml -->
<div class="container">
  <canvas ref="canvas1"></canvas>
  <select @change="change">
    <option value="value1">LinearGradient</option>
    <option value="value2">RadialGradient</option>
    <option value="value3">shadowBlur</option>
    <option value="value4">shadowOffset</option>
  </select>
</div>

/* xxx.css */
.container{
  width: 100%;
  height: 100%;
  flex-direction: column;
  justify-content: center;
  align-items: center;
  background-color: #F1F3F5;
}
canvas{
  width: 600px;
  height: 500px;
  background-color: #fdfdfd;
  border: 5px solid red;
}
select{
  margin-top: 50px;
  width: 250px;
  height: 100px;
  background-color: white;
}

// xxx.js
export default {
  data:{
    el: null,
    ctx: null,
  },
  onShow(){
    this.el = this.$refs.canvas1;
    this.ctx = this.el.getContext("2d",{antialias: true});
    // 创建一个线性渐变色
    let gradient = this.ctx.createLinearGradient(100,100, 400,300);
    // 添加渐变颜色
    gradient.addColorStop(0.0, 'red');
    gradient.addColorStop(0.7, 'white');
    gradient.addColorStop(1.0, 'green');
    // 填充颜色为渐变色
    this.ctx.fillStyle = gradient;
    this.ctx.fillRect(100, 100, 400, 300);
  },
  change(e){
    if(e.newValue == 'value1'){
      // 清除画布上的内容
      this.ctx.clearRect(0,0,600,500);
      let gradient = this.ctx.createLinearGradient(100,100, 400,300);
      gradient.addColorStop(0.0, 'red');
      gradient.addColorStop(0.7, 'white');
      gradient.addColorStop(1.0, 'green');
      this.ctx.fillStyle = gradient;
      // 设置绘制阴影时的模糊级别
      this.ctx.shadowBlur = 0;
      // 绘制阴影时和原有对象的垂直偏移值
      this.ctx.shadowOffsetY = 0;
      // 绘制阴影时和原有对象的水平偏移值
      this.ctx.shadowOffsetX = 0;
      this.ctx.fillRect(100, 100, 400, 300);
    }else if(e.newValue == 'value2'){
      this.ctx.clearRect(0,0,600,500);
      // 创建一个径向渐变色
      let gradient = this.ctx.createRadialGradient(300,250,20,300,250,100);
      gradient.addColorStop(0.0, 'red');
      gradient.addColorStop(0.7, 'white');
      gradient.addColorStop(1.0, 'green');
      this.ctx.shadowBlur = 0;
      this.ctx.shadowOffsetY = 0;
      this.ctx.shadowOffsetX = 0;
      this.ctx.fillStyle = gradient;
      this.ctx.fillRect(100, 100, 400, 300);
    }else if(e.newValue == 'value3'){
      this.ctx.clearRect(0,0,600,500);
      let gradient = this.ctx.createLinearGradient(100,100, 400,400);             
      gradient.addColorStop(0.0, 'red');    
      gradient.addColorStop(0.5, 'white');    
      gradient.addColorStop(1, '#17ea35');
      // 设置绘制阴影时的模糊级别
      this.ctx.shadowBlur = 30;
      // 绘制阴影时的阴影颜色
      this.ctx.shadowColor = 'rgb(229, 16, 16)';
      this.ctx.fillStyle = gradient;
      this.ctx.fillRect(100, 100, 400, 300);
    }else if(e.newValue == 'value4'){
      this.ctx.clearRect(0,0,600,500);
      this.ctx.clearRect(0,0,600,500);
      let gradient = this.ctx.createRadialGradient(300,250,20,300,250,200);      
      gradient.addColorStop(0.0, 'red');     
      gradient.addColorStop(0.5, 'white');     
      gradient.addColorStop(1, '#17ea35');
      // 设置绘制阴影时的模糊级别
      this.ctx.shadowBlur = 30;     
      this.ctx.shadowOffsetY = 30;
      // 绘制阴影时的阴影颜色
      this.ctx.shadowColor = 'rgb(23, 1, 1)';
      this.ctx.fillStyle = gradient;
      this.ctx.fillRect(100, 100, 400, 300);
    }
  },
}

HarmonyOS Developer Canvas开发指导-鸿蒙开发者社区

填充文字

先创建文本，再用fillText方法把文字写在画布上。通过globalAlpha属性改变基线透明度，使基线不会挡住文字，再设置textAlign和textBaseline属性确定文字基于基线的位置。

<!-- xxx.hml -->
<div class="container">
  <canvas ref="canvas1"></canvas>
  <select @change="change">
    <option value="value1">text</option>
    <option value="value2">textBaseline</option>
    <option value="value3">textAlign</option>
  </select>
</div>

/* xxx.css */
.container{
  width: 100%;
  height: 100%;
  flex-direction: column;
  justify-content: center;
  align-items: center;
  background-color: #F1F3F5;
}
canvas{
  width: 600px;
  height: 500px;
  background-color: #fdfdfd;
  border: 5px solid red;
}
select{
  margin-top: 50px;
  width: 250px;
  height: 100px;
  background-color: white;
}

// xxx.js
export default {
  data:{
    el: null,
    ctx: null,
  },
  onShow(){
    this.el = this.$refs.canvas1;
    this.ctx = this.el.getContext("2d",{antialias: true});
    // 创建文本
    let text = "Hello World";
    // 设置字体
    this.ctx.font = '30px';
    this.ctx.fillText("with:"+this.ctx.measureText(text).width, 200, 300);
    // 填充字体文本
    this.ctx.fillText(text, 200, 250);
  },
  change(e){
    if(e.newValue == 'value1'){
      // 清除画布上的内容
      this.ctx.clearRect(0,0,600,500);
      // 开始新的路径
      this.ctx.beginPath();
      // 初始化textAlign值
      this.ctx.textAlign = 'left';
      // 初始化textBaseline
      this.ctx.textBaseline = 'alphabetic';
      // 设置字体
      this.ctx.font = '30px';
      let text = "Hello World";
      // 获取字体width
      this.ctx.fillText("with:"+this.ctx.measureText(text).width, 200, 300);
      // 填充字体文本
      this.ctx.fillText(text, 200, 250);
    }else if(e.newValue == 'value2'){
      this.ctx.clearRect(0,0,600,500);
      this.ctx.beginPath();
      // 设置透明度
      this.ctx.globalAlpha = 0.1;
      // 设置线宽度
      this.ctx.lineWidth = 10;
      // 设置线段颜色
      this.ctx.strokeStyle = '#0000ff';
      // 从当前点移动到指定点
      this.ctx.moveTo(0, 240);
      // 当前点到指定点进行路径连接
      this.ctx.lineTo(600, 240);
      this.ctx.stroke();
      this.ctx.font = '35px';
      this.ctx.globalAlpha = 1;
      // 初始化textAlign值
      this.ctx.textAlign = 'left';
      // 设置textBaseline
      this.ctx.textBaseline = 'top';
      this.ctx.fillText('Top', 50, 240);
      this.ctx.textBaseline = 'bottom';
      this.ctx.fillText('Bottom', 200, 240);
      this.ctx.textBaseline = 'middle';
      this.ctx.fillText('Middle', 400, 240);
    }else if(e.newValue == 'value3'){
      // 清除画布上的内容
      this.ctx.clearRect(0,0,600,500);
      this.ctx.beginPath();
      this.ctx.globalAlpha = 0.1;
      this.ctx.lineWidth = 10;
      this.ctx.strokeStyle = '#0000ff';
      this.ctx.moveTo(300, 0);
      this.ctx.lineTo(300, 500);
      this.ctx.stroke();
      this.ctx.font = '35px';
      this.ctx.globalAlpha = 1;
      // 初始化 textBaseline
      this.ctx.textBaseline = 'alphabetic';
      // 设置textAlign
      this.ctx.textAlign = 'left';
      this.ctx.fillText('textAlign=left',300, 100);
      this.ctx.textAlign = 'center';
      this.ctx.fillText('textAlign=center',300, 250);
      this.ctx.textAlign = 'right';
      this.ctx.fillText('textAlign=right',300, 400);
    }
  }
}

HarmonyOS Developer Canvas开发指导-鸿蒙开发者社区

说明

ltr布局模式下start和left一致，rtl布局模式下start和right一致·。

添加图片

创建图片对象后使用drawImage属性画出图片，给图片设置一些动画样式如scale（缩放）、translate（平移）或rotate（旋转）。

<!-- xxx.hml -->
<div class="container">
  <div class="content">
    <canvas ref="canvas0"></canvas>
    <text onclick="change">change</text>
    <canvas ref="canvas1"></canvas>
    <text onclick="rotate">rotate</text>
    <canvas ref="canvas2"></canvas>
    <text onclick="scale">scale</text>
    <canvas ref="canvas3"></canvas>
    <text onclick="translate" style="width: 300px;">translate</text>
    <canvas ref="canvas4"></canvas>
    <text onclick="transform" style="width: 300px;">transform</text>
    <canvas ref="canvas5"></canvas>
    <text onclick="setTransform" style="width: 300px;">setTransform</text>
    <canvas ref="canvas6"></canvas>
  </div>
</div>

/* xxx.css */
.container{
  width: 100%;
  flex-direction: column;
  background-color: #F1F3F5;
  align-items: center;
}
canvas{
  width: 600px;
  height: 300px;
  margin-bottom: 100px;
  background-color: #fdfdfd;
  border: 5px solid red;
}
.content{
  width: 80%;
  margin-top: 50px;
  margin-bottom: 50px;
  display: flex;
  flex-wrap: wrap;
  justify-content: space-around;
}
text{
  font-size: 35px;
  width: 200px;
  height: 80px;
  color: white;
  border-radius: 20px;
  text-align: center;
  background-color: #6060e7;
  margin-bottom: 30px;
}

// xxx.js
import promptAction from '@ohos.promptAction';
export default {
  data:{
    compositeOperation: 'source-over'
  },
  onShow(){
    let ctx = this.$refs.canvas0.getContext("2d");
    // 创建图片对象
    let img = new Image();
    // 设置图片路径
    img.src = 'common/images/2.png';
    // 设置图片宽度
    img.width= 150;
    // 设置图片高度
    img.height=150;
    // 图片平铺容器
    var pat = ctx.createPattern(img, 'repeat');ctx.fillStyle = pat;
    ctx.fillRect(0, 0, 600, 300);
  },
  change(){
    // 创建画布后得到画笔
    let ctx = this.$refs.canvas1.getContext("2d");
    ctx.clearRect(0,0,600,1000);
    if(this.compositeOperation == "source-over"){
      this.compositeOperation = "destination-over";
    }else{
      this.compositeOperation = "source-over";
    }
    ctx.globalCompositeOperation = this.compositeOperation;
    let img = new Image();
    img.src = 'common/images/2.png';
    // 图片成功获取触发方法
    img.onload = function() {
      ctx.drawImage(img, 150, 20, 200, 200);
    };
    let img1 = new Image();
    img1.src = 'common/images/3.png';
    img1.onload = function() {
      // 画上图片
      ctx.drawImage(img1, 250, 80, 200, 200);
    };
    // 图片获取失败触发方法
    img1.onerror = function() {
      promptAction.showToast({message:"error",duration:2000})
    };
  },
  rotate(){
    let ctx = this.$refs.canvas2.getContext("2d");
    ctx.clearRect(0,0,600,300);
    // 旋转
    ctx.rotate(10 * Math.PI / 180);
    let img = new Image();
    img.src = 'common/images/2.png';
    img.onload = function() {
      ctx.drawImage(img, 300, 0, 100, 100);
    };
  },
  scale(){
    let ctx = this.$refs.canvas3.getContext("2d");
    ctx.clearRect(0,0,600,200);
    // 缩放
    ctx.scale(1.3,1.2);
    let img = new Image();
    img.src = 'common/images/2.png';
    img.onload = function() {
      ctx.drawImage(img, 0, 0, 50, 50);
    };
  },
  translate(){
    let ctx = this.$refs.canvas4.getContext("2d");
    ctx.clearRect(0,0,600,300);
    ctx.translate(10,0);
    let img = new Image();
    img.src = 'common/images/2.png';
    img.onload = function() {
      ctx.drawImage(img, 0, 50, 300, 200);
    };
  },
  transform(){
    let ctx = this.$refs.canvas5.getContext("2d");
    ctx.clearRect(0,0,600,300);
    ctx.transform(1.1, 0.1, 0.1, 1, 10, 0);
    let img = new Image();
    img.src = 'common/images/2.png';
    img.onload = function() {
      ctx.drawImage(img, 0, 50, 100, 100);
     };
  },
  setTransform(){
    let ctx = this.$refs.canvas6.getContext("2d");
    ctx.clearRect(0,0,600,300);
    ctx.setTransform(1.1, 0.1, 0.1, 1, 10, 0);
    let img = new Image();
    img.src = 'common/images/2.png';
    img.onload = function() {
      ctx.drawImage(img, 0, 50, 100, 100);
    };
  },
}

HarmonyOS Developer Canvas开发指导-鸿蒙开发者社区

说明

setTransfrom方法使用的参数和transform()方法相同，但setTransform()方法会重置现有的变换矩阵并创建新的变换矩阵。
变换后的坐标计算方式（x和y为变换前坐标，x'和y'为变换后坐标）：
x' = scaleX * x + skewY * y + translateX
y' = skewX * x + scaleY * y + translateY

添加方法

save方法可对画笔样式进行存储，restore可对存储的画笔进行恢复。如下面的示例，先设置画笔为红色，在保存画笔后对画布进行清除并改变画笔为蓝色，当我们直接使用画笔时会画出一个蓝色矩形，对存储的画笔进行恢复后就可画出红色矩形。

<!-- xxx.hml -->
<div class="container">
  <div class="content">
    <canvas ref="canvas"></canvas>
  </div>
  <div class="content">
    <text onclick="save">save</text>
    <text onclick="clear">clear</text>
    <text onclick="restore">restore</text>
  </div>
</div>

/* xxx.css */
.container{
  width: 100%;
  height: 100%;
  flex-direction: column;
  background-color: #F1F3F5;
  align-items: center;
}
canvas{
  margin-top: 300px;
  width: 600px;
  height: 500px;
  background-color: #fdfdfd;
  border: 5px solid red;
}
.content{
  width: 80%;
  margin-top: 50px;
  margin-bottom: 50px;
  display: flex;
  flex-wrap: wrap;
  justify-content: space-around;
}
text{
  width: 150px;
  height: 80px;
  color: white;
  border-radius: 20px;
  text-align: center;
  background-color: #6060e7;
  margin-bottom: 30px;
}

// xxx.js
import promptAction from '@ohos.promptAction';
export default {
  data:{
    ctx: '',
  },
  onShow(){
    this.ctx = this.$refs.canvas.getContext("2d");
    this.ctx.fillStyle = "red"
    this.ctx.fillRect(200, 150, 200, 200);
  },
  save(){
    // 画笔储存
    this.ctx.save();
    promptAction.showToast({message:"save succeed"});
  },
  clear(){ 
    this.ctx.clearRect(0,0,600,500);
    // 该变画笔颜色
    this.ctx.fillStyle = "#2133d2";
  },
  restore(){
    this.ctx.beginPath();
    // 画笔恢复
    this.ctx.restore();    
    this.ctx.fillRect(200, 150, 200, 200);
  },
}

HarmonyOS Developer Canvas开发指导-鸿蒙开发者社区

Path2D对象

路径对象，支持通过对象的接口进行路径的描述，并通过Canvas的stroke接口进行绘制。具体请参考Path2D对象。

画线段

创建Path2D，使用多条线段组合图形。

<!-- xxx.hml --> 
<div class="container">
  <canvas ref="canvas"></canvas>
</div>

/* xxx.css */
.container {
    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: 5px solid red;
}

// xxx.js
export default {
    onShow() {
        let ctx = this.$refs.canvas.getContext('2d', {
            antialias: true
        });
        let path = ctx.createPath2D();
        // 房顶
        path.moveTo(10, 300);
        path.lineTo(210, 100);
        path.lineTo(410, 300);
        // 屋子
        path.moveTo(10, 300);
        path.lineTo(410, 300);
        path.lineTo(410, 600);
        path.lineTo(10, 600);
        path.closePath();
        // 窗子
        path.moveTo(50, 450);
        path.bezierCurveTo(70, 350, 130, 350, 150, 450);
        path.closePath();
        // 门
        path.moveTo(250, 450);
        path.rect(250, 450, 100, 600);
        path.closePath();
        // 烟囱
        path.moveTo(365, 250);
        path.ellipse(310, 215, 30, 130, 0, Math.PI * 0.04, Math.PI * 1.1, 1);
        // 树
        path.moveTo(485, 450);
        path.quadraticCurveTo(510, 500, 485, 600);
        path.moveTo(550, 450);
        path.quadraticCurveTo(525, 500, 550, 600);
        path.moveTo(600, 535);
        path.arc(520, 450, 85, 0, 6);
        ctx.stroke(path);
    }
}

HarmonyOS Developer Canvas开发指导-鸿蒙开发者社区

画图形

先使用createPath2D创建出路径对象，只对path1路径进行描边，所以画布上就只会出现path1的路径图形。点击text组件触发addPath方法会把path2路径对象当参数传入path1中，再对path1对象进行描边（stroke）操作后画布出现path1和path2两个图形。点击change文本改变setTransform属性值为setTransform(2, 0.1, 0.1, 2, 0,0)，图形变大并向左倾斜。

<!-- xxx.hml -->
<div class="container">
    <canvas ref="canvas"></canvas>
    <div class="content">
        <text onclick="addPath">{{ isAdd }}</text>
        <text onclick="setTransform">{{ textName }}</text>
    </div>
</div>

/* xxx.css */
.container {
    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: 5px solid red;
}

.content {
    width: 80%;
    margin-top: 50px;
    margin-bottom: 50px;
    display: flex;
    flex-wrap: wrap;
    justify-content: space-around;
}

text {
    width: 150px;
    height: 80px;
    color: white;
    border-radius: 20px;
    text-align: center;
    background-color: #6060e7;
    margin-bottom: 30px;
}

// xxx.js
export default {
    data: {
        ctx: null,
        path1: null,
        path2: null,
        path3: null,
        isAdd: "addPath2",
        isChange: true,
        textName: 'change'
    },
    onShow() {
        this.ctx = this.$refs.canvas.getContext('2d', {
            antialias: true
        });
        this.path1 = this.ctx.createPath2D();
        // 正方形
        this.path1.moveTo(200, 200);
        this.path1.lineTo(400, 200);
        this.path1.lineTo(400, 400);
        this.path1.lineTo(200, 400);
        this.path1.closePath();
        this.path2 = this.ctx.createPath2D();
        // 圆形
        this.path2.arc(300, 300, 75, 0, 6.28);
        this.ctx.stroke(this.path1);
    },
    addPath() {
        if (this.isAdd == "addPath2") {
            // 删除指定指定区域的绘制内容
            this.ctx.clearRect(0, 0, 600, 600);
            this.ctx.beginPath();
            // 将另一个的路径添加到当前路径对象中
            this.path2.addPath(this.path1);
            this.ctx.stroke(this.path2);
            this.isAdd = "clearPath2";
        } else {
            this.ctx.clearRect(0, 0, 600, 600);
            this.ctx.stroke(this.path1);
            this.isAdd = "addPath2";
        }
    },
    setTransform() {
        if (this.isChange) {
            this.ctx.clearRect(0, 0, 600, 600);
            this.path3 = this.ctx.createPath2D();
            this.path3.arc(150, 150, 100, 0, 6.28);
            // 重置现有的变换矩阵并创建新的变换矩阵
            this.path3.setTransform(2, 0.1, 0.1, 2, 0, 0);
            this.ctx.stroke(this.path3);
            this.isChange = !this.isChange;
            this.textName = "back"
        } else {
            this.ctx.clearRect(0, 0, 600, 600);
            this.path3.setTransform(0.5, -0.1, -0.1, 0.5, 0, 0);
            this.ctx.stroke(this.path3);
            this.isChange = !this.isChange;
            this.textName = "change";
        }
    }
}

HarmonyOS Developer Canvas开发指导-鸿蒙开发者社区

OffscreenCanvasRenderingContext2D对象

使用OffscreenCanvas在离屏Canvas画布组件上进行绘制，绘制对象可以是矩形、文本、图片等。离屏，即GPU在当前缓冲区以外新开辟的一个缓冲区。具体请参考OffscreenCanvasRenderingContext2D对象。

以下示例创建了一个OffscreenCanvas画布，再在画布上创建一个getContext2d对象，并设置filter属性改变图片样式。

<!-- xxx.hml -->
<div class="container">
  <canvas ref="canvas1"></canvas>
  <select @change="change()">
    <option value="blur(5px)">blur</option>
    <option value="grayscale(50%)">grayscale</option>
    <option value="hue-rotate(45deg)">hue-rotate</option>
    <option value="invert(100%)">invert</option>
    <option value="drop-shadow(8px 8px 10px green)">drop-shadow</option>
    <option value="brightness(0.4)">brightness</option>
    <option value="opacity(0.25)">opacity</option>
    <option value="saturate(30%)">saturate</option>
    <option value="sepia(60%)">sepia</option>
    <option value="contrast(200%)">contrast</option>
  </select>
</div>

/* xxx.css */
.container{
  width: 100%;
  height: 100%;
  flex-direction: column;
  justify-content: center;
  align-items: center;
  background-color: #F1F3F5;
}
canvas{
  width: 600px;
  height: 500px;
  background-color: #fdfdfd;
  border: 5px solid red;
}
select{
  margin-top: 50px;
  width: 250px;
  height: 100px;
  background-color: white;
}

// xxx.js
import promptAction from '@ohos.promptAction';
export default {
  data:{
    el: null,
    ctx: null,
    offscreen: null,
    offCanvas: null,
    img: null,
  },
  onShow(){
    this.ctx = this.$refs.canvas1.getContext("2d");
    this.offscreen = new OffscreenCanvas(600, 500);
    this.offCanvas = this.offscreen.getContext("2d");
    this.img = new Image();
    this.img.src = 'common/images/2.png';
    // 图片成功获取触发方法
    let _this = this;
    this.img.onload = function() {
      _this.offCanvas.drawImage(_this.img, 100, 100, 400, 300);
    };
    this.img.onerror = function() {
      promptAction.showToast({message:"error",duration:2000})
    };
    var bitmap = this.offscreen.transferToImageBitmap();    this.ctx.transferFromImageBitmap(bitmap);
  },
  change(e){
    this.offCanvas.filter = e.newValue;this.offCanvas.drawImage(this.img, 100, 100, 400, 300);
    var bitmap = this.offscreen.transferToImageBitmap();
    this.ctx.transferFromImageBitmap(bitmap);
  },
}

HarmonyOS Developer Canvas开发指导-鸿蒙开发者社区

判断位置

使用isPointInPath判断坐标点是否在路径的区域内，使用isPointInStroke判断坐标点是否在路径的边缘线上，并在页面上显示返回结果。

<!-- xxx.hml -->
<div class="container">
  <div class="content">
    <text>坐标：{{X}}, {{Y}}</text>
    <text>In path:{{textValue}}</text>
    <text>In stroke:{{textValue1}}</text>
  </div>
  <canvas ref="canvas"></canvas>
  <button onclick="change">Add(50)</button>
</div>

/* xxx.css */
.container{
  width: 100%;
  height: 100%;
  flex-direction: column;
  justify-content: center;
  align-items: center;
  background-color: #F1F3F5;
}
canvas{
  width: 600px;
  height: 500px;
  background-color: #fdfdfd;
  border: 5px solid red;
}
.content{
  flex-direction: column;
  justify-content: center;
  align-items: center; 
}
text{
  font-size: 30px;
  width: 300px;
  height: 80px;
  text-align: center;
}
button{
  width: 180px;
  height: 75px;
  margin-top: 50px;
}

// xxx.js
export default {
  data: {
    textValue: 0,
    textValue1: 0,
    X:0,
    Y:250,
  },
  onShow(){
    let canvas = this.$refs.canvas.getContext('2d');
    let offscreen = new OffscreenCanvas(500,500);
    let offscreenCanvasCtx = offscreen.getContext("2d");
    let offscreenCanvasCtx1 = offscreen.getContext("2d");
    offscreenCanvasCtx1.arc(this.X, this.Y, 2, 0, 6.28);
    offscreenCanvasCtx.lineWidth=20;
    offscreenCanvasCtx.rect(200,150, 200, 200);
    offscreenCanvasCtx.stroke();
    this.textValue1 = offscreenCanvasCtx.isPointInStroke(this.X, this.Y)?'true':'false';
    this.textValue = offscreenCanvasCtx.isPointInPath(this.X, this.Y)?'true':'false';
    let bitmap = offscreen.transferToImageBitmap();
    canvas.transferFromImageBitmap(bitmap);
  },
  change(){
    if(this.X < 500){
      this.X = this.X+50;
    }else{
      this.X = 0;
    }
    let canvas = this.$refs.canvas.getContext('2d');
    let offscreen = new OffscreenCanvas(500,500);
    let offscreenCanvasCtx = offscreen.getContext("2d");
    let offscreenCanvasCtx1 = offscreen.getContext("2d");
    offscreenCanvasCtx1.arc(this.X, this.Y, 1, 0, 6.28)
    offscreenCanvasCtx.lineWidth=20
    offscreenCanvasCtx.rect(200,150, 200, 200);
    offscreenCanvasCtx.stroke();
    this.textValue1 = offscreenCanvasCtx.isPointInStroke(this.X, this.Y)?'true':'false';
    this.textValue = offscreenCanvasCtx.isPointInPath(this.X, this.Y)?'true':'false';
    let bitmap = offscreen.transferToImageBitmap();
    canvas.transferFromImageBitmap(bitmap);
  }
}

HarmonyOS Developer Canvas开发指导-鸿蒙开发者社区