_initShaderPass() {
        // create our frame buffer
        if(!this.target) {
            this._createFrameBuffer();
        }
        else {
            // set the render target
            this.setRenderTarget(this.target);
            this.target._shaderPass = this;
        }

        // create a texture from the render target texture
        const texture = new Texture(this.renderer, {
            sampler: "uRenderTexture",
            isFBOTexture: true,
            fromTexture: this.target.getTexture(),
        });

        texture.addParent(this);

        // onReady callback
        this.loader._setLoaderSize(0);

        this._canDraw = true;

        // be sure we'll update the scene even if drawing is disabled
        this.renderer.needRender();
    }
Here we init additionnal shader pass planes properties
     This mainly consists in creating our render texture and add a frame buffer object
*