does onDraw in a surfaceview container causes video to be invalidated?

Question

I have a video view. This view is contained inside a custom FrameLayout called VideoStructure, where I can put also a channel logo or things alike. Under normal conditions, the video is hardware accelerated, so the view is (i suppose) really a transparent "black hole", while the video is decoded & rendered by the relevant hardware.

My question is, if I override draw() in the Video View's container (the VideoStructure extends FrameLayout in the image) to draw some stuff (ie. the circle in the image) OVER the video -I'm overriding draw(), not onDraw()- will this break the hardware acceleration? Can I expect a big performance hit for doing this?

Answer 1

It should have no effect on performance.

SurfaceViews have two parts, the "view" part, and the "surface" part. The "view" part is a transparent hole that fits in with the other views, the "surface" part is a completely independent layer that is composited with the view layer by the system. The video is being sent to the "surface" part.

If you override SurfaceView's "view" renderer, you'll get a hardware-accelerated Canvas for a View that is normally completely transparent (so if you erase it, you better use an alpha of zero and the correct transfer mode).

If you attempt to render on the "surface" part, by getting a Canvas from lockCanvas(), you will either fail (because the video effectively has it locked), or succeed and prevent video from being written to it.

The system compositor is going to have to blend the "view" and "surface" layers no matter what appears in the "view" layer, so making a few more pixels opaque isn't going to have a measurable impact.

Update: see the graphics architecture doc for more details on Surfaces and composition.