Couldn’t the rounded corners of a video also be an overlay?
I’m sure I’m missing something here, but the article does not explain that point.
That means you have to power up the 3d part of the GPU to do that (because the renderer does it in shaders).
Where as if you add some 9 pixels of black above/below to account for the rounded corner, there is no clipping of the video and you can use hardware scanout planes.
That's important because keeping the 3d part of the GPU turned off is a huge power savings. And the scanout plane can already scale for you to the correct size.
No because the clipping is done in the client after the content is drawn. The client doesn't have the full screen contents. To make it work with an overlay, the clipping would have to be moved to the server. There could be another extension that lets you pass an alpha mask texture to the server to use as a clip mask. But this doesn't exist (yet?)