问题描述：

将SceneCapture2DActor的SceneCaptureComponent2D的RenderTarget格式设为PF_A16B16G16R16格式, 将captureSource类型设为SceneColorSceneDepth，（SceneCaptureComponent2D->CaptureSource = ESceneCaptureSource::SCS_SceneColorSceneDepth），但生成的RenderTarget的a通道被截取到了1，无法获取到深度信息。
查看源码，用到的shader是MobileSceneCapture.usf文件。看不出来啥问题。
然后把SceneCaptureComponent2D的captureSource类型改为SCS_SceneDepth：

/** Specifies which component of the scene rendering should be output to the final render target. */
UENUM()
enum ESceneCaptureSource 
{ 
	SCS_SceneColorHDR UMETA(DisplayName="SceneColor (HDR) in RGB, Inv Opacity in A"),
	SCS_SceneColorHDRNoAlpha UMETA(DisplayName="SceneColor (HDR) in RGB, 0 in A"),
	SCS_FinalColorLDR UMETA(DisplayName="Final Color (LDR) in RGB"),
	SCS_SceneColorSceneDepth UMETA(DisplayName="SceneColor (HDR) in RGB, SceneDepth in A"),
	SCS_SceneDepth