微信小游戏中three.js实现离屏画布-创新互联

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在微信小游戏中，把three.js的3D内容在离屏画布处理，然后复制到在屏画布，方法是：

let c_toolbarHeight=140;
 
let sysInfo=wx.getSystemInfoSync();
require('./js/libs/weapp-adapter.js');
var canvas_webGL=window.canvas;
canvas_webGL.width = sysInfo.screenWidth * sysInfo.pixelRatio;
canvas_webGL.height = (sysInfo.screenHeight-c_toolbarHeight) * sysInfo.pixelRatio;
var ctx_webGL=canvas_webGL.getContext('webgl');
 
let options={context: ctx_webGL}
let renderer = new THREE.WebGLRenderer(options);
renderer.setSize(sysInfo.screenWidth, sysInfo.screenHeight-c_toolbarHeight);
renderer.setPixelRatio(sysInfo.pixelRatio);
 
function render(){
  //清除canvas_bkg的3D区域
  wx.tmGlobal.eraseZone(0,
    c_toolbarHeight,
    sysInfo.screenWidth,
    sysInfo.screenHeight);
  renderer.render(scene, camera);
  wx.tmGlobal.ctx_bkg.drawImage(canvas_webGL,
    0,c_toolbarHeight*sysInfo.pixelRatio);
  //画一条横的红线
  wx.tmGlobal.ctx_bkg.strokeStyle = '#FF8C00';
  wx.tmGlobal.ctx_bkg.lineWidth = 2;
  wx.tmGlobal.ctx_bkg.beginPath();
  wx.tmGlobal.ctx_bkg.moveTo(0,
    (c_toolbarHeight)*sysInfo.pixelRatio);
  wx.tmGlobal.ctx_bkg.lineTo(
    sysInfo.screenWidth*sysInfo.pixelRatio,
    (c_toolbarHeight)*sysInfo.pixelRatio);
  //画游戏结束临界线
  wx.tmGlobal.ctx_bkg.moveTo(0,
    (c_toolbarHeight+c_yugaoHeight)*sysInfo.pixelRatio);
  wx.tmGlobal.ctx_bkg.lineTo(
    sysInfo.screenWidth*sysInfo.pixelRatio,
    (c_toolbarHeight+c_yugaoHeight)*sysInfo.pixelRatio);
  wx.tmGlobal.ctx_bkg.stroke();
  //把canvas_bkg画到在屏画布
  wx.tmGlobal.ctx_main.clearRect(0,0,
    wx.tmGlobal.canvas_main.width,wx.tmGlobal.canvas_main.height);
    wx.tmGlobal.ctx_main.drawImage(wx.tmGlobal.canvas_bkg,0,0);
}