在上篇文章中渲染物体用到了 SwapChain，如下：

            if (mUiHelper.isReadyToRender()) {
                if (mRenderer.beginFrame(mSwapChain, frameTimeNanos)) {
                    mRenderer.render(mView);
                    mRenderer.endFrame();
                }
            }

   SwapChain 我们在前面文章中提到，是把它看做画布来理解的。那么它是在什么时候？又是

如何创建的呢？ 下面我们一起学习一下 SwapChain 的构建过程。我们先看一下 SwapChain文件

中做的解释：

/**
 * A <code>SwapChain</code> represents an Operating System's <b>native</b> renderable surface.
 *
 * <p>Typically it's a native window or a view. Because a <code>SwapChain</code> is initialized
 * from a native object, it is given to filament as an <code>Object</code>, which must be of the
 * proper type for each platform filament is running on.</p>
 *
 * <code>
 * SwapChain swapChain = engine.createSwapChain(nativeWindow);
 * </code>
 *
 * <p>The <code>nativeWindow</code> parameter above must be of type:</p>
 *
 * <center>
 * <table border="1">
 *     <tr><th> Platform </th><th> nativeWindow type </th></tr>
 *     <tr><td> Android </td><td>{@link android.view.Surface Surface}</td></tr>
 * </table>
 * </center>
 * <p>
 *
 * <h1>Examples</h1>
 *
 * <h2>Android</h2>
 *
 *
 * <p>A {@link android.view.Surface Surface} can be retrieved from a
 * {@link android.view.SurfaceView SurfaceView} or {@link android.view.SurfaceHolder SurfaceHolder}
 * easily using {@link android.view.SurfaceHolder#getSurface SurfaceHolder.getSurface()} and/or
 * {@link android.view.SurfaceView#getHolder SurfaceView.getHolder()}.</p>
 *
 * <p>To use a {@link android.view.TextureView Textureview} as a <code>SwapChain</code>, it is
 * necessary to first get its {@link android.graphics.SurfaceTexture SurfaceTextu