微信小游戏中three.js离屏画布華華的博客-

国庆8天长假，重庆之行因故未成，偶得闲，用three.js结合cannon.js写个3D小游戏耍耍。

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); }

在vivo和iphone手机都表现正常，但是，华为手机显示不出来：

https://developers.weixin.qq.com/community/develop/doc/00026c3c1c8eb010de384a82d51000?jumpto=

其它用户也提了好久了，腾讯或华为都没有解决，试来试去，终于找到了另一种写法：

renderer = new THREE.WebGLRenderer(); let target = new THREE.WebGLRenderTarget(     sysInfo.screenWidth*sysInfo.pixelRatio,      (sysInfo.screenHeight-c_toolbarHeight)*sysInfo.pixelRatio); renderer.setRenderTarget(target); gl=renderer.getContext(); ​ var canvas_huawei=wx.createCanvas(); canvas_huawei.width=sysInfo.screenWidth*sysInfo.pixelRatio; canvas_huawei.height=(sysInfo.screenHeight-c_toolbarHeight)*sysInfo.pixelRatio; var ctx_huawei=canvas_huawei.getContext('2d'); ​ var canvas_huawei2=wx.createCanvas(); canvas_huawei2.width=sysInfo.screenWidth*sysInfo.pixelRatio; canvas_huawei2.height=(sysInfo.screenHeight-c_toolbarHeight)*sysInfo.pixelRatio; var ctx_huawei2=canvas_huawei2.getContext('2d'); ​ var imageData = ctx_huawei.createImageData(     sysInfo.screenWidth*sysInfo.pixelRatio,     (sysInfo.screenHeight-c_toolbarHeight)*sysInfo.pixelRatio); var pixels = new Uint8Array(imageData.data.length); ​ function render(){     //擦除背景画布的webGL区域（因为webGL是用的透明绘制）     wx.tmGlobal.eraseZone(0,         c_toolbarHeight,         sysInfo.screenWidth,         sysInfo.screenHeight);     renderer.render(scene, camera);     gl.readPixels(             0,             0,             gl.drawingBufferWidth,             gl.drawingBufferHeight,             gl.RGBA,gl.UNSIGNED_BYTE,pixels);     imageData.data.set(pixels);     ctx_huawei.putImageData(imageData,0,0);     //清除           ctx_huawei2.clearRect(0,0,canvas_huawei2.width,canvas_huawei2.height);     //上下镜像翻转     ctx_huawei2.translate(0,canvas_huawei2.height);     ctx_huawei2.scale(1, -1);     ctx_huawei2.drawImage(canvas_huawei,0,0);     //恢复     ctx_huawei2.translate(0,canvas_huawei2.height);     ctx_huawei2.scale(1, -1);     wx.tmGlobal.ctx_bkg.drawImage(canvas_huawei2,             0,c_toolbarHeight*sysInfo.pixelRatio);     ...... }