canvas.uvue

<template>
  <view class="page" id="page-canvas">

    <canvas id="canvas" class="canvas-element"></canvas>
    <scroll-view class="scroll-view">
      <view>
        <text style="padding: 8px 10px;">获取 CanvasContext</text>
      </view>
      <button class="canvas-drawing-button" id="useAsync" @click="useAsync">异步方式获取 CanvasContext</button>
      <button class="canvas-drawing-button" id="useSync" @click="useSync">同步方式获取 CanvasContext</button>
      <view class="text-group">
        <text>获取 CanvasContext 结果：</text>
        <text id="testCanvasContext">{{testCanvasContext}}</text>
      </view>
      <view class="text-group">
        <text>测试 ToDataURL 结果：</text>
        <text id="testToDataURLResult">{{testToDataURLResult}}</text>
      </view>
      <!-- #ifdef WEB -->
      <button class="canvas-drawing-button" @click="canvasToBlob">canvasToBlob</button>
      <view>
        <text>testToBlobResult: {{testToBlobResult}}</text>
      </view>
      <!-- #endif -->
      <button class="canvas-drawing-button" id="toDataURL" @click="canvasToDataURL">canvasToDataURL</button>
      <view class="text-group" v-if="dataBase64.length>0">
        <text>canvasToDataURL:</text>
        <text>{{dataBase64.slice(0,22)}}...</text>
      </view>
      <view style="padding: 8px 10px;">CanvasContext API 演示</view>
      <view class="grid-view">
        <view class="grid-item" v-for="(name, index) in names" :key="index">
          <button class="canvas-drawing-button" @click="handleCanvasButton(name)">{{name}}</button>
        </view>
      </view>

    </scroll-view>
  </view>

</template>

<script>
  function hidpi(canvas : UniCanvasElement) {
    const context = canvas.getContext("2d")!;
    const dpr = uni.getDeviceInfo().devicePixelRatio ?? 1;
    canvas.width = canvas.offsetWidth * dpr;
    canvas.height = canvas.offsetHeight * dpr;
    context.scale(dpr, dpr);
  }

  const API_PATH = ["arc", "arcTo", "bezierCurveTo", "quadraticCurve", "moveTo", "lineTo", "rect", "clip", "pattern"]
  const API_DRAW = ["stroke", "strokeRect", "strokeText", "fill", "fillRect", "fillText", "drawImage", "drawImageLocal", "clearRect"]
  const API_STATE = ["beginPath", "closePath", "reset", "transform", "rotate", "resetTransform", "save", "restore", "scale", "translate"]
  const API_PROPERTIES = ["setLineCap", "setLineJoin", "setLineWidth", "setMiterLimit", "setFillStyle", "setStrokeStyle", "setGlobalAlpha", "setFontSize", "lineDash", "linearGradient", "radialGradient", "textAlign"]

  export default {
    data() {
      return {
        title: 'Context2D',
        canvas: null as UniCanvasElement | null,
        canvasContext: null as CanvasRenderingContext2D | null,
        canvasWidth: 0,
        canvasHeight: 0,
        dataBase64: '',
        // 仅测试
        testCanvasContext: false,
        testToBlobResult: false,
        testToDataURLResult: false,
        names: [...API_PATH, ...API_DRAW, ...API_STATE, ...API_PROPERTIES, "measureText"] as string[],
        image: null as Image | null,
        // 仅测试
        testCreateCanvasContextAsyncSuccess: false,
      }
    },
    onReady() {
      this.useAsync()
    },
    methods: {
      // #ifdef WEB
      canvasToBlob() {
        this.canvas!.toBlob((blob : Blob) => {
          this.testToBlobResult = (blob.size > 0 && blob.type == 'image/jpeg')
        }, 'image/jpeg', 0.95)
      },
      // #endif
      canvasToDataURL() {
        this.dataBase64 = this.canvas!.toDataURL()
      },
      useAsync() {

        // HBuilderX 4.25+
        // 异步调用方式, 跨平台写法
        uni.createCanvasContextAsync({
          id: 'canvas',
          component: this,
          success: (context : CanvasContext) => {
            const canvasContext = context.getContext('2d')!;
            const canvas = canvasContext.canvas;
            if (this.canvasContext == null) {


              this.canvasContext = canvasContext
              this.testCanvasContext = true

              hidpi(canvas);
              this.canvasWidth = canvas.width;
              this.canvasHeight = canvas.height;
              canvasContext.save()
            }

            this.measureText()
            this.testToDataURLResult = canvas.toDataURL().startsWith('data:image/png;base64')
            this.canvas = canvas;
          }
        })

      },
      useSync() {

        let canvas = uni.getElementById("canvas") as UniCanvasElement

        this.canvasContext = canvas.getContext("2d")
        this.testCanvasContext = true
        this.canvasContext!.save()
        // hidpi(canvas);
        this.canvasWidth = canvas.width;
        this.canvasHeight = canvas.height;
        this.arc()

        // #ifdef WEB
        canvas.toBlob((blob : Blob) => {
          this.testToBlobResult = (blob.size > 0 && blob.type == 'image/jpeg')
        }, 'image/jpeg', 0.95)
        // #endif
        this.testToDataURLResult = canvas.toDataURL().startsWith('data:image/png;base64')

        this.canvas = canvas;

      },

      clearCanvasRect() {
        this.canvasContext!.clearRect(0, 0, this.canvasWidth, this.canvasHeight)
      },
      handleCanvasButton(name : string) {
        switch (name) {
          case "arc":
            this.arc();
            break;
          case "arcTo":
            this.arcTo();
            break;
          case "beginPath":
            this.beginPath();
            break;
          case "bezierCurveTo":
            this.bezierCurveTo();
            break;
          case "clearRect":
            this.clearRect();
            break;
          case "clip":
            this.clip();
            break;
          case "closePath":
            this.closePath();
            break;
          case "pattern":
            this.pattern()
            break;
          case "linearGradient":
            this.createLinearGradient();
            break;
          case "radialGradient":
            this.createRadialGradient();
            break;
          case "fill":
            this.fill();
            break;
          case "fillRect":
            this.fillRect();
            break;
          case "fillText":
            this.fillText();
            break;
          case "lineTo":
            this.lineTo();
            break;
          case "moveTo":
            this.moveTo();
            break;
          case "quadraticCurve":
            this.quadraticCurveTo();
            break;
          case "rect":
            this.rect();
            break;
          case "reset":
            this.reset();
            break;
          case "resetTransform":
            this.resetTransform();
            break;
          case "restore":
            this.restore();
            break;
          case "rotate":
            this.rotate();
            break;
          case "save":
            this.save();
            break;
          case "scale":
            this.scale();
            break;
          case "stroke":
            this.stroke();
            break;
          case "strokeRect":
            this.strokeRect();
            break;
          case "strokeText":
            this.strokeText();
            break;
          case "transform":
            this.transform();
            break;
          case "translate":
            this.translate();
            break;
          case "drawImageLocal":
            this.drawImageLocal()
            break;
          case "drawImage":
            this.drawImage();
            break;
          case "measureText":
            this.measureText();
            break;
          case "setFillStyle":
            this.setFillStyle();
            break;
          case "setStrokeStyle":
            this.setStrokeStyle();
            break;
          case "setGlobalAlpha":
            this.setGlobalAlpha();
            break;
          case "setFontSize":
            this.setFontSize();
            break;
          case "setLineCap":
            this.setLineCap();
            break;
          case "setLineJoin":
            this.setLineJoin();
            break;
          case "lineDash":
            this.lineDash();
            break;
          case "setLineWidth":
            this.setLineWidth();
            break;
          case "setMiterLimit":
            this.setMiterLimit();
            break;
          case "textAlign":
            this.textAlign();
          default:
            break;
        }
      },
      arc() {
        const context = this.canvasContext!

        context.save()
        this.clearCanvasRect()
        context.beginPath()
        context.lineWidth = 2
        context.arc(75, 75, 50, 0, Math.PI * 2, true)
        context.moveTo(110, 75)
        context.arc(75, 75, 35, 0, Math.PI, false)
        context.moveTo(65, 65)
        context.arc(60, 65, 5, 0, Math.PI * 2, true)
        context.moveTo(95, 65)
        context.arc(90, 65, 5, 0, Math.PI * 2, true)
        context.stroke()

        context.restore()
      },
      arcTo() {
        const context = this.canvasContext!

        context.save()
        this.clearCanvasRect()
        context.beginPath()
        context.moveTo(150, 20)
        context.arcTo(150, 100, 50, 20, 30)
        context.stroke()

        context.fillStyle = "blue"
        // base point
        context.fillRect(150, 20, 10, 10)

        context.fillStyle = "red"
        // control point one
        context.fillRect(150, 100, 10, 10)
        // control point two
        context.fillRect(50, 20, 10, 10)
        //
        context.setLineDash([5, 5])
        context.moveTo(150, 20)
        context.lineTo(150, 100)
        context.lineTo(50, 20)
        context.stroke()
        context.beginPath()
        context.arc(120, 38, 30, 0, 2 * Math.PI, true)
        context.stroke()

        context.restore()
      },
      beginPath() {
        const context = this.canvasContext!

        context.save()
        this.clearCanvasRect()
        // First path
        context.beginPath()
        context.strokeStyle = "blue"
        context.moveTo(20, 20)
        context.lineTo(200, 20)
        context.stroke()

        // Second path
        context.beginPath()
        context.strokeStyle = "green"
        context.moveTo(20, 20)
        context.lineTo(120, 120)
        context.stroke()

        context.restore()
      },
      textAlign() {
        const context = this.canvasContext!

        context.save()
        this.clearCanvasRect()
        context.beginPath()
        context.moveTo(150, 0)
        context.lineTo(150, 150)
        context.stroke()

        context.font = "30px serif"

        context.textAlign = "left"
        context.fillText("left-aligned", 150, 40)

        context.textAlign = "center"
        context.fillText("center-aligned", 150, 85)

        context.textAlign = "right"
        context.fillText("right-aligned", 150, 130)

        context.restore()
      },
      bezierCurveTo() {
        const context = this.canvasContext!

        context.save()
        this.clearCanvasRect()
        context.beginPath()
        context.moveTo(50, 20)
        context.bezierCurveTo(230, 30, 150, 60, 50, 100)
        context.stroke()

        context.fillStyle = "blue"
        // start point
        context.fillRect(50, 20, 10, 10)
        // end point
        context.fillRect(50, 100, 10, 10)

        context.fillStyle = "red"
        // control point one
        context.fillRect(230, 30, 10, 10)
        // control point two
        context.fillRect(150, 70, 10, 10)

        context.restore()
      },
      clearRect() {
        const context = this.canvasContext!

        context.save()
        this.clearCanvasRect()
        // 绘制黄色背景
        context.beginPath()
        context.fillStyle = "#ff6"
        context.fillRect(0, 0, 300, 150)

        // 绘制蓝色三角形
        context.beginPath()
        context.fillStyle = "blue"
        context.moveTo(20, 20)
        context.lineTo(180, 20)
        context.lineTo(130, 130)
        context.closePath()
        context.fill()

        // 清除一部分画布
        context.clearRect(10, 10, 120, 100)

        context.restore()
      },
      clip() {
        const context = this.canvasContext!

        context.save()
        this.clearCanvasRect()
        // Create circular clipping region
        context.beginPath();
        context.arc(100, 75, 50, 0, Math.PI * 2, true)
        context.clip()

        // Draw stuff that gets clipped
        context.fillStyle = "blue"
        context.fillRect(0, 0, 300, 150)
        context.fillStyle = "orange"
        context.fillRect(0, 0, 100, 100)

        context.restore()
      },
      closePath() {
        const context = this.canvasContext!

        context.save()
        this.clearCanvasRect()
        context.beginPath()
        context.lineWidth = 10
        context.moveTo(20, 20)
        context.lineTo(20, 100)
        context.lineTo(70, 100)
        context.closePath()
        context.stroke()

        context.restore()
      },
      pattern() {
        const context = this.canvasContext!

        const image = new Image(100, 100)
        image.src = '../../../static/api.png';
        image.onload = () => {
          context.save()
          this.clearCanvasRect()
          const pattern = context.createPattern(image, "repeat")
          context.fillStyle = pattern
          context.fillRect(0, 0, 100, 100)
          context.restore()
        };
      },
      createLinearGradient() {
        const context = this.canvasContext!

        context.save()
        this.clearCanvasRect()
        // Create a linear gradient
        // The start gradient point is at x=20, y=0
        // The end gradient point is at x=220, y=0
        const gradient = context.createLinearGradient(20, 0, 220, 0)

        // Add three color stops
        gradient.addColorStop(0, "green")
        gradient.addColorStop(0.5, "cyan")
        gradient.addColorStop(1, "green")

        // Set the fill style and draw a rectangle
        context.fillStyle = gradient
        context.fillRect(20, 20, 200, 100)

        context.restore()
      },
      createRadialGradient() {
        const context = this.canvasContext!

        context.save()
        this.clearCanvasRect()
        // Create a radial gradient
        // The inner circle is at x=110, y=90, with radius=30
        // The outer circle is at x=100, y=100, with radius=70
        const gradient = context.createRadialGradient(110, 90, 30, 100, 100, 70)

        // Add three color stops
        gradient.addColorStop(0, "pink")
        gradient.addColorStop(0.9, "white")
        gradient.addColorStop(1, "green")

        // Set the fill style and draw a rectangle
        context.fillStyle = gradient
        context.fillRect(20, 20, 160, 160)

        context.restore()
      },
      fill() {
        const context = this.canvasContext!

        context.save()
        this.clearCanvasRect()
        context.beginPath()
        context.rect(20, 20, 150, 100)
        context.strokeStyle = '#00ff00'
        context.fill()

        context.restore()
      },
      fillRect() {
        const context = this.canvasContext!

        context.save()
        this.clearCanvasRect()
        context.fillStyle = "green"
        context.fillRect(20, 10, 150, 100)

        context.restore()
      },
      fillText() {
        const context = this.canvasContext!

        context.save()
        this.clearCanvasRect()
        context.strokeStyle = '#ff0000'

        context.beginPath()
        context.moveTo(0, 10)
        context.lineTo(300, 10)
        context.stroke()
        // context.save()
        // context.scale(1.5, 1.5)
        // context.translate(20, 20)
        // context.setFontSize(10)
        context.fillText('Hello World', 0, 30, 300)
        // context.setFontSize(20)
        context.fillText('Hello World', 100, 30, 300)

        // context.restore()

        context.beginPath()
        context.moveTo(0, 30)
        context.lineTo(300, 30)
        context.stroke()

        context.restore()
      },
      moveTo() {
        const context = this.canvasContext!

        context.save()
        this.clearCanvasRect()
        context.beginPath()
        context.moveTo(0, 0)
        context.lineTo(300, 150)
        context.stroke()

        context.restore()
      },
      lineTo() {
        const context = this.canvasContext!

        context.save()
        this.clearCanvasRect()
        context.beginPath()
        context.moveTo(20, 20)
        context.lineTo(20, 100)
        context.lineTo(70, 100)
        context.stroke()

        context.restore()
      },
      stroke() {
        const context = this.canvasContext!

        context.save()
        this.clearCanvasRect()
        context.beginPath()
        context.moveTo(20, 20)
        context.lineTo(20, 100)
        context.lineTo(70, 100)
        context.strokeStyle = '#00ff00'
        context.stroke()

        context.restore()
      },
      strokeRect() {
        const context = this.canvasContext!

        context.save()
        this.clearCanvasRect()
        context.strokeStyle = "green"
        context.strokeRect(20, 10, 160, 100)

        context.restore()
      },
      strokeText() {
        const context = this.canvasContext!

        context.save()
        this.clearCanvasRect()
        context.font = "10px serif"
        context.strokeText("Hello world", 50, 90)

        context.font = "30px serif"
        context.strokeStyle = "blue"
        context.strokeText("Hello world", 50, 100)

        context.restore()
      },
      rotate() {
        const context = this.canvasContext!

        context.save()
        this.clearCanvasRect()
        // Point of transform origin
        context.arc(0, 0, 5, 0, 2 * Math.PI, true)
        context.fillStyle = "blue"
        context.fill()

        // Non-rotated rectangle
        context.fillStyle = "gray"
        context.fillRect(100, 0, 80, 20)
        // Rotated rectangle
        context.rotate((45 * Math.PI) / 180)
        context.fillStyle = "red"
        context.fillRect(100, 0, 80, 20)

        // Reset transformation matrix to the identity matrix
        context.setTransform(1, 0, 0, 1, 0, 0)

        context.restore()
      },
      scale() {
        const context = this.canvasContext!

        context.save()
        this.clearCanvasRect()
        // Scaled rectangle
        context.scale(9, 3)
        context.fillStyle = "red"
        context.fillRect(10, 10, 8, 20)

        // Reset current transformation matrix to the identity matrix
        context.setTransform(1, 0, 0, 1, 0, 0)

        // Non-scaled rectangle
        context.fillStyle = "gray"
        context.fillRect(10, 10, 8, 20)

        context.restore()
      },
      reset() {
        const context = this.canvasContext!
        context.save()
        this.clearCanvasRect()

        // Set line width
        context.lineWidth = 10
        context.strokeStyle = '#00ff00'
        // Stroke rect outline
        context.strokeRect(50, 50, 150, 100)

        // Create filled text
        context.font = "50px serif";
        context.fillText("Rect!", 70, 110)


        context.lineWidth = 5

        // Stroke out circle
        context.beginPath();
        context.arc(300, 100, 50, 0, 2 * Math.PI)
        context.stroke();

        // Create filled text
        context.font = "25px sans-serif"
        context.fillText("Circle!", 265, 100)
        // context.reset()

        hidpi(uni.getElementById("canvas") as UniCanvasElement)
        context.restore()
      },
      translate() {
        const context = this.canvasContext!

        context.save()
        this.clearCanvasRect()
        // Moved square
        context.translate(110, 30)
        context.fillStyle = "red"
        context.fillRect(0, 0, 80, 80)

        // Reset current transformation matrix to the identity matrix
        context.setTransform(1, 0, 0, 1, 0, 0)

        // Unmoved square
        context.fillStyle = "gray"
        context.fillRect(0, 0, 80, 80)

        context.restore()
      },
      save() {
        const context = this.canvasContext!
        this.clearCanvasRect()
        context.save()
        context.beginPath()
        context.strokeStyle = '#00ff00'
        context.scale(2, 2)
        context.strokeStyle = '#ff0000'
        context.rect(0, 0, 100, 100)
        context.stroke()
        context.restore()

        context.save()
        context.rect(0, 0, 50, 50)
        context.stroke()

        context.restore()
      },
      restore() {
        const context = this.canvasContext!;
        this.clearCanvasRect();
        [3, 2, 1].forEach((item) => {
          context.save()
          context.beginPath()
          context.scale(item, item)
          context.rect(10, 10, 100, 100)
          context.stroke()
          context.restore()
        })
      },
      drawImageLocal() {
        const context = this.canvasContext!
        this.clearCanvasRect()
        const image = new Image(100, 100)
        image.src = '../../../static/uni.png'
        image.onload = () => {
          context.drawImage(image, 0, 0, 100, 100)
        }
      },
      drawImage() {
        const context = this.canvasContext!
        this.clearCanvasRect()
        const image = new Image(100, 100);
        image.src = 'https://web-ext-storage.dcloud.net.cn/uni-app-x/hello-uniappx-qrcode.png'
        image.onload = () => {
          context.drawImage(image, 0, 0, 100, 100)
        }
      },
      rect() {
        const context = this.canvasContext!

        context.save()
        this.clearCanvasRect()
        context.beginPath()
        context.rect(20, 20, 150, 100)
        context.stroke()

        context.restore()
      },
      quadraticCurveTo() {
        const context = this.canvasContext!

        context.save()
        this.clearCanvasRect()
        // Quadratic Bézier curve
        context.beginPath()
        context.moveTo(50, 20)
        context.quadraticCurveTo(230, 30, 50, 100)
        context.stroke()

        // Start and end points
        context.fillStyle = "blue"
        context.beginPath()
        context.arc(50, 20, 5, 0, 2 * Math.PI, true) // Start point
        context.arc(50, 100, 5, 0, 2 * Math.PI, true) // End point
        context.fill();

        // Control point
        context.fillStyle = "red"
        context.beginPath()
        context.arc(230, 30, 5, 0, 2 * Math.PI, true)
        context.fill()

        context.restore()
      },
      resetTransform() {
        const context = this.canvasContext!

        context.save()
        this.clearCanvasRect()
        // Draw a rotated rectangle
        context.rotate((45 * Math.PI) / 180)
        context.fillRect(60, 0, 100, 30)

        // Reset transformation matrix to the identity matrix
        context.resetTransform()
        context.fillStyle = "red"
        context.fillRect(60, 0, 100, 30)

        context.restore()
      },
      transform() {
        const context = this.canvasContext!

        context.save()
        this.clearCanvasRect()
        context.transform(1, 0.2, 0.8, 1, 0, 0)
        context.fillRect(0, 0, 100, 100)

        context.restore()
      },
      setFillStyle() {
        const context = this.canvasContext!

        context.save()
        this.clearCanvasRect();
        ['#fef957', 'rgb(242,159,63)', 'rgb(242,117,63)', '#e87e51'].forEach((item : string, index : number) => {
          context.fillStyle = item
          context.beginPath()
          context.rect(0 + 75 * index, 0, 50, 50)
          context.fill()
        })

        context.restore()
      },
      setStrokeStyle() {
        const context = this.canvasContext!

        context.save()
        this.clearCanvasRect();
        ['#fef957', 'rgb(242,159,63)', 'rgb(242,117,63)', '#e87e51'].forEach((item : string, index : number) => {
          context.strokeStyle = item
          context.beginPath()
          context.rect(0 + 75 * index, 0, 50, 50)
          context.stroke()
        })

        context.restore()
      },
      setGlobalAlpha() {
        const context = this.canvasContext!

        context.save()
        this.clearCanvasRect()
        context.fillStyle = '#000000';
        [1, 0.5, 0.1].forEach((item : number, index : number) => {
          context.globalAlpha = item
          context.beginPath()
          context.rect(0 + 75 * index, 0, 50, 50)
          context.fill()
        })
        context.globalAlpha = 1

        context.restore()
      },
      setFontSize() {
        const context = this.canvasContext!

        context.save();
        [10, 20, 30, 40].forEach((item : number, index : number) => {
          context.font = item + 'px serif'
          context.fillText('Hello, world', 20, 20 + 40 * index)
        })

        context.restore()
      },
      setLineCap() {
        const context = this.canvasContext!

        context.save()
        this.clearCanvasRect()
        context.lineWidth = 10;
        ['butt', 'round', 'square'].forEach((item : string, index : number) => {
          context.beginPath()
          context.lineCap = item
          context.moveTo(20, 20 + 20 * index)
          context.lineTo(100, 20 + 20 * index)
          context.stroke()
        })

        context.restore()
      },
      setLineJoin() {
        const context = this.canvasContext!

        context.save()
        this.clearCanvasRect()
        context.lineWidth = 10;
        ['bevel', 'round', 'miter'].forEach((item : string, index : number) => {
          context.beginPath()
          context.lineJoin = item
          context.moveTo(20 + 80 * index, 20)
          context.lineTo(100 + 80 * index, 50)
          context.lineTo(20 + 80 * index, 100)
          context.stroke()
        })

        context.restore()
      },
      setLineWidth() {
        const context = this.canvasContext!

        context.save()
        this.clearCanvasRect();
        [2, 4, 6, 8, 10].forEach((item : number, index : number) => {
          context.beginPath()
          context.lineWidth = item
          context.moveTo(20, 20 + 20 * index)
          context.lineTo(100, 20 + 20 * index)
          context.stroke()
        })

        context.restore()
      },
      lineDash() {
        const context = this.canvasContext!

        context.save();
        this.clearCanvasRect()
        context.setLineDash([4, 16])

        // Dashed line with no offset
        context.beginPath()
        context.moveTo(0, 50)
        context.lineTo(300, 50)
        context.stroke()

        // Dashed line with offset of 4
        context.beginPath()
        context.strokeStyle = "red"
        context.lineDashOffset = 4
        context.moveTo(0, 100)
        context.lineTo(300, 100)
        context.stroke()

        context.restore()
      },
      setMiterLimit() {
        const context = this.canvasContext!

        context.save()
        this.clearCanvasRect()
        context.lineWidth = 4;
        [2, 4, 6, 8, 10].forEach((item : number, index : number) => {
          context.beginPath()
          context.miterLimit = item
          context.moveTo(20 + 80 * index, 20)
          context.lineTo(100 + 80 * index, 50)
          context.lineTo(20 + 80 * index, 100)
          context.stroke()
        })

        context.restore()
      },
      measureText() {
        const context = this.canvasContext!

        context.save()
        this.clearCanvasRect()
        const text = "uni-app x，是下一代 uni-app，是一个跨平台应用开发引擎"

        context.font = "20px 宋体"

        context.fillStyle = "red"
        context.fillText(text, 0, 60)
        const textMetrics = context.measureText(text)
        context.strokeText(text, 40, 100)
        context.fillText("measure text width:" + textMetrics.width, 40, 80)

        context.restore()
      }
    }
  }
</script>

<style>
  .page {
    flex: 1;
    height: 100%;
    overflow: hidden;
  }

  .scroll-view {
    flex: 1;
  }

  .canvas-element {
    width: 100%;
    height: 250px;
    background-color: #ffffff;
  }

  .grid-view {
    padding: 10px;
    flex-direction: row;
    flex-wrap: wrap;
  }

  .btn-to-image {
    margin: 10px;
  }

  .grid-item {
    width: 50%;
    padding: 5px;
  }

  .btn-to-image {
    margin: 10px;
  }

  .text-group {
    display: flex;
    flex-flow: row nowrap;
    justify-content: space-between;
    align-items: center;
    padding: 8px 10px;
  }
</style>