如何使用SceneForm从ViewRenderable/Node生成对应bitmap？

可实现的三种方案（按匹配度从高到低排序） #

方案1：Filament离屏渲染（100%匹配AR场景显示效果）

该方案基于SceneForm底层的Filament渲染引擎实现，可完整保留ViewRenderable在AR场景中的透视变形、透明通道、光照、旋转缩放效果，和实际显示效果完全一致：

• 从ArSceneView实例中获取Filament核心实例：

  val engine = arSceneView.engine
  val renderer = arSceneView.renderer
  val currentCamera = arSceneView.scene.camera
  

• 创建对应分辨率的离屏渲染纹理，开启RGBA通道保留透明效果：

  val outputWidth = 1080 // 可自定义输出宽度
  val outputHeight = 1920 // 可自定义输出高度
  val offscreenTexture = Texture.Builder()
      .width(outputWidth)
      .height(outputHeight)
      .format(Texture.InternalFormat.RGBA8)
      .usage(Texture.Usage.COLOR_ATTACHMENT or Texture.Usage.COPY_SRC)
      .build(engine)
  val renderTarget = RenderTarget.Builder()
      .attachTexture(RenderTarget.AttachmentPoint.COLOR, offscreenTexture)
      .build(engine)
  

• 对齐渲染参数和当前AR相机参数，渲染ViewRenderable到离屏纹理：

  renderer.renderStandalone(
      renderTarget,
      listOf(yourViewRenderableNode), // 仅传入需要截图的节点
      currentCamera.viewMatrix,
      currentCamera.projectionMatrix,
      null,
      null
  )
  

• 读取纹理像素转成Bitmap：

  val buffer = ByteBuffer.allocateDirect(outputWidth * outputHeight * 4)
  engine.readTexture(
      offscreenTexture,
      0, 0, 0,
      outputWidth, outputHeight,
      0,
      Texture.Format.RGBA,
      Texture.Type.UBYTE,
      buffer
  )
  buffer.rewind()
  val resultBitmap = Bitmap.createBitmap(outputWidth, outputHeight, Bitmap.Config.ARGB_8888)
  resultBitmap.copyPixelsFromBuffer(buffer)
  

• 用完后销毁纹理和渲染目标避免内存泄漏：

  engine.destroy(renderTarget)
  engine.destroy(offscreenTexture)
  

方案2：全屏截图裁剪（实现成本最低）

如果目标ViewRenderable没有被其他3D节点遮挡，可通过全屏截图裁剪实现，代码量最小：

• 调用SceneForm封装的截图方法拿到全屏AR帧：

  arSceneView.captureSingleFrame { fullScreenBitmap ->
      // 计算目标节点的屏幕边界矩形
      val nodePosition = yourViewRenderableNode.worldPosition
      val screenPoint = arSceneView.worldToScreenPoint(nodePosition)
      val nodeWidth = (yourViewRenderable.sizer as ViewSizer).size.x
      val nodeHeight = (yourViewRenderable.sizer as ViewSizer).size.y
      // 换算边界坐标后裁剪
      val left = (screenPoint.x - nodeWidth/2).coerceAtLeast(0f).toInt()
      val top = (screenPoint.y - nodeHeight/2).coerceAtLeast(0f).toInt()
      val width = nodeWidth.toInt().coerceAtMost(fullScreenBitmap.width - left)
      val height = nodeHeight.toInt().coerceAtMost(fullScreenBitmap.height - top)
      val resultBitmap = Bitmap.createBitmap(fullScreenBitmap, left, top, width, height)
      fullScreenBitmap.recycle()
  }
  

方案3：原始View直接截图（无3D效果，仅适用于平面无变形场景）

如果你的ViewRenderable不需要保留AR场景中的3D透视、旋转效果，可直接截取传入ViewRenderable的原始View：

val targetView = yourViewRenderable.view
targetView.measure(
    View.MeasureSpec.makeMeasureSpec(targetView.layoutParams.width, View.MeasureSpec.EXACTLY),
    View.MeasureSpec.makeMeasureSpec(targetView.layoutParams.height, View.MeasureSpec.EXACTLY)
)
targetView.layout(0, 0, targetView.measuredWidth, targetView.measuredHeight)
val resultBitmap = Bitmap.createBitmap(targetView.measuredWidth, targetView.measuredHeight, Bitmap.Config.ARGB_8888)
val canvas = Canvas(resultBitmap)
targetView.draw(canvas)

内容的提问来源于stack exchange，提问作者Monster Brain