<template>
  <view class="page">
    <page-head :title="title"></page-head>
    <button @click="startRequestAnimationFrame">requestAnimationFrame</button>
    <button @click="stopRequestAnimationFrame">cancelAnimationFrame</button>
    <text class="frame-count">FPS: {{FPSString}}</text>
    <text class="frame-count">FrameCount: {{testFrameCount}}</text>
    <text class="tips">提示: 在当前测试例子中，每增加一次调用 requestAnimationFrame 帧率翻倍，cancelAnimationFrame 后恢复</text>
  </view>
</template>

<script>
  export default {
    data() {
      return {
        title: 'AnimationFrame',
        taskId: 0,
        FPSString: '- / -ms',
        lastTime: 0,
        frameCount: 0,
        testFrameCount: 0
      }
    },
    onUnload() {
      if (this.taskId > 0) {
        this.stopRequestAnimationFrame()
      }
    },
    methods: {
      startRequestAnimationFrame() {
        this.taskId = requestAnimationFrame((timestamp : number) => {
          this.updateFPS(timestamp)
          this.testFrameCount++
          this.startRequestAnimationFrame()
        })
      },
      stopRequestAnimationFrame() {
        cancelAnimationFrame(this.taskId)
        this.lastTime = 0
        this.frameCount = 0
        this.FPSString = '- / -ms'
      },
      updateFPS(timestamp : number) {
        this.frameCount++
        if (timestamp - this.lastTime >= 1000) {
          const timeOfFrame = (1000 / this.frameCount)
          this.FPSString = `${this.frameCount} / ${timeOfFrame.toFixed(3)}ms`
          this.frameCount = 0
          this.lastTime = timestamp
        }
      }
    }
  }
</script>

<style>
  .page {
    padding: 15px;
  }

  .frame-count {
    margin-top: 15px;
  }

  .tips {
    font-size: 12px;
    margin-top: 30px;
    opacity: 0.7;
  }
</style>
