[0]setSubPixels画布擦除不掉

 this.btn.label = Math.random().toString();

        // console.log(Math.random());

        let tex:Laya.Texture = Laya.Loader.getRes(this.bUrl);

        

        let x:number = this._testStatus == true ? 0:50;//Math.random()>0.5 ? 50 : 0;       

        this._testStatus = !this._testStatus;



        // let canvasInfo = this.getCanvasWidthHeight();



        let ctx = new Laya.Context();

        // let w = canvasInfo.w//tex.width;

        // let h = canvasInfo.h//tex.height;



        let w = tex.width;

        let h = tex.height;



        ctx.size(w,h);

        ctx.asBitmap = true;

        // ctx.clearRect(0,0,w,h);

        

        let  _targets= ctx['_targets'];

        _targets.start();

        ctx.clear();

        this.drawTex(ctx,this.bUrl,x,0);

        // this.drawTex(ctx,this.cUrl,x,0);

        ctx.flush();

        _targets.end();

        _targets.restore();

        let dt = _targets.getData(0, 0, w, h);//像素数据

        ctx.destroy();



        if(!this.aImg){

            let aImg:Laya.Image = new Laya.Image(this.aUrl);

            aImg.scaleX = aImg.scaleY = 2;

            Laya.stage.addChild(aImg);

            aImg.mouseEnabled = false;

            this.aImg = aImg;

        }



        //清除目标纹理的像素

        let _sourceTex:Laya.Texture = Laya.Loader.getRes(this.aUrl);

        let ret = new Uint8Array(_sourceTex.width * _sourceTex.height * 4);

        let tex2d:Laya.Texture2D = this.aImg.source["_bitmap"];

        tex2d.setPixels(ret);//填充像素数据



        //该操作在vulkan中会有杂点,directX opengl没有问题

        tex2d.setSubPixels(0,0,w,h,dt);// 这里有问题 注释掉 在微信小游戏vulkan驱动环境下 没有清屏(噪点和上次画布残留像素数据)





        // this.clearTexture();//清除目标纹理的像素



        // tex2d.getPixels();

        /*

        let p1 = this.aImg.source.getPixels(0,0,tex2d.width,tex2d.height);

        let tex1 = new Laya.Texture2D(tex2d.width,tex2d.height);

        tex1.setPixels(p1);

        let tex22:Laya.Texture = new Laya.Texture();

        tex22.bitmap = tex1;

        this.aImg.source = tex22;



        console.log("time:"+Laya.timer.currTimer);

        

        Laya.timer.once(1000,this,()=>{

            console.log("time:"+Laya.timer.currTimer);

            // tex2d

            tex1.setSubPixels(0,0,w,h,dt);// 这里有问题

        })

*/