Use new OMX_DISPLAY_ALPHA_FLAGS_DISCARD_LOWER_LAYERS flag to avoid having to blank screen

Note: Requires updated firmware

Author: popcornmix

OMXVideo.cpp

@@ -217,6 +217,10 @@ bool COMXVideo::PortSettingsChanged()
   configDisplay.num = m_config.display;
   configDisplay.layer = m_config.layer;
   configDisplay.transform = m_transform;
+
+  if (!(m_config.dst_rect.x2 > m_config.dst_rect.x1 && m_config.dst_rect.y2 > m_config.dst_rect.y1))
+    configDisplay.alpha |= OMX_DISPLAY_ALPHA_FLAGS_DISCARD_LOWER_LAYERS;
+
   omx_err = m_omx_render.SetConfig(OMX_IndexConfigDisplayRegion, &configDisplay);
   if(omx_err != OMX_ErrorNone)
   {
@@ -912,6 +916,9 @@ void COMXVideo::SetAlpha(int alpha)
   configDisplay.set = OMX_DISPLAY_SET_ALPHA;
   configDisplay.alpha = alpha;
 
+  if (!(m_config.dst_rect.x2 > m_config.dst_rect.x1 && m_config.dst_rect.y2 > m_config.dst_rect.y1))
+    configDisplay.alpha |= OMX_DISPLAY_ALPHA_FLAGS_DISCARD_LOWER_LAYERS;
+
   omx_err = m_omx_render.SetConfig(OMX_IndexConfigDisplayRegion, &configDisplay);
   if(omx_err != OMX_ErrorNone)
   {