在 React Konva 中播放 Canvas 上的视频

Question

基于 Konva 关于如何将视频渲染到 canvas 的文档，我想通过直接从 Konva.Image 实例访问视频参考来播放视频。下面是一个人为的示例，用于模拟我从组件外部动态播放视频的目标。即使 imageRef.current.image() returns 视频元素参考，下面的视频也没有按预期播放。关于如何访问视频参考有什么建议吗？

import React, { useEffect, useContext, useState } from 'react'
import { Image } from "react-konva";
import Konva from 'konva'

 export const MainVideo = ({ shape, dispatch  }) =>  {
  const imageRef = React.useRef(null);
  const video = document.createElement('video');
  video.setAttribute('src',shape.url);


  useEffect(() => {
    if(imageRef) {

  imageRef.current.image().play();
  const layer = imageRef.current.getLayer();

  const anim = new Konva.Animation(() => {
  }, layer);

        anim.start()

    }
  }, [imageRef])

    return (
     <Image 
     ref={imageRef}
     opacity={shape.o}
     id={shape.id} 
     image={video} 
     x={shape.x} 
     y={shape.y} 
     zIndex={0}
     height={360}
     width={640} />
    )
}

Answer 1

你可以这样做：

const Video = ({ src }) => {
  const imageRef = React.useRef(null);
  const [size, setSize] = React.useState({ width: 50, height: 50 });

  // we need to use "useMemo" here, so we don't create new video elment on any render
  const videoElement = React.useMemo(() => {
    const element = document.createElement("video");
    element.src = src;
    return element;
  }, [src]);

  // when video is loaded, we should read it size
  React.useEffect(() => {
    const onload = function() {
      setSize({
        width: videoElement.videoWidth,
        height: videoElement.videoHeight
      });
    };
    videoElement.addEventListener("loadedmetadata", onload);
    return () => {
      videoElement.removeEventListener("loadedmetadata", onload);
    };
  }, [videoElement]);

  // use Konva.Animation to redraw a layer
  React.useEffect(() => {
    videoElement.play();
    const layer = imageRef.current.getLayer();

    const anim = new Konva.Animation(() => {}, layer);
    anim.start();

    return () => anim.stop();
  }, [videoElement]);

  return (
    <Image
      ref={imageRef}
      image={videoElement}
      x={20}
      y={20}
      stroke="red"
      width={size.width}
      height={size.height}
      draggable
    />
  );
};

演示：https://codesandbox.io/s/react-konva-video-on-canvas-oygvf

在 React Konva 中播放 Canvas 上的视频

Play video on Canvas in React Konva

javascript

konvajs

react-konva