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>
      <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>

      <view class="text-group">
        <text>测试 createImage 结果：</text>
        <text id="testCreateImage">{{testCreateImage}}</text>
      </view>

      <view class="text-group">
        <text>测试 createPath2D 结果：</text>
        <text id="testCreatePath2D">{{testCreatePath2D}}</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>
      <button @click="onCreateImage">createImage</button>
      <button @click="onCreatePath2D">createPath2D</button>
      <view style="padding: 8px 10px;">CanvasContext API 演示</view>
      <navigator url="./canvas-context">
        <button>CanvasContext API</button>
      </navigator>

    </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);
  }

  export default {
    data() {
      return {
        title: 'Context2D',
        canvas: null as UniCanvasElement | null,
        canvasContext: null as CanvasContext | null,
        renderingContext: null as CanvasRenderingContext2D | null,
        canvasWidth: 0,
        canvasHeight: 0,
        dataBase64: '',
        // 仅测试
        testCanvasContext: false,
        testToBlobResult: false,
        testToDataURLResult: false,
        testCreateCanvasContextAsyncSuccess: false,
        testCreateImage: false,
        testCreatePath2D: false
      }
    },
    onReady() {
      // HBuilderX 4.25+
      // 异步调用方式, 跨平台写法
      uni.createCanvasContextAsync({
        id: 'canvas',
        component: this,
        success: (context : CanvasContext) => {
          this.canvasContext = context;
          this.renderingContext = context.getContext('2d')!;
          this.canvas = this.renderingContext!.canvas;

          hidpi(this.canvas!);
          this.canvasWidth = this.canvas!.width;
          this.canvasHeight = this.canvas!.height;

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

      // 同步调用方式，仅支持 app/web
      // let canvas = uni.getElementById("canvas") as UniCanvasElement
      // this.renderingContext = canvas.getContext("2d")
      // hidpi(canvas);
      // this.canvas = canvas;
      // this.canvasWidth = canvas.width;
      // this.canvasHeight = canvas.height;
    },
    methods: {
      // #ifdef WEB
      canvasToBlob() {
        this.canvasContext!.toBlob((blob : Blob) => {
          this.testToBlobResult = (blob.size > 0 && blob.type == 'image/jpeg')
        }, 'image/jpeg', 0.95)
      },
      // #endif
      canvasToDataURL() {
        this.dataBase64 = this.canvasContext!.toDataURL()
      },
      onCreateImage() {
        this.renderingContext!.clearRect(0, 0, this.canvasWidth, this.canvasHeight)
        let image = this.canvasContext!.createImage();
        image.src = "../../static/logo.png"
        image.onload = () => {
          this.testCreateImage = true
          this.renderingContext?.drawImage(image, 0, 0, 100, 100);
        }
      },
      onCreatePath2D() {
        this.renderingContext!.clearRect(0, 0, this.canvasWidth, this.canvasHeight)
        const context = this.renderingContext!
        let path2D = this.canvasContext!.createPath2D()
        this.testCreatePath2D = true
        const amplitude = 64;
        const wavelength = 64;
        for (let i = 0; i < 5; i++) {
          const x1 = 0 + (i * wavelength);
          const y1 = 128;
          const x2 = x1 + wavelength / 4;
          const y2 = y1 - amplitude;
          const x3 = x1 + 3 * wavelength / 4;
          const y3 = y1 + amplitude;
          const x4 = x1 + wavelength;
          const y4 = y1;
          context.moveTo(x1, y1);
          path2D.bezierCurveTo(x2, y2, x3, y3, x4, y4);
        }
        context.stroke(path2D);
      }
    }
  }
</script>

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

  .scroll-view {
    flex: 1;
  }

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

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

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