<html> <head> <style></style></head> <body class='hmmessage'><div dir='ltr'> <div>> Date: Wed, 25 Nov 2015 16:18:52 +0000 > Subject: Re: Process for implementing a double buffer on Wayland > From: daniel@fooishbar.org > To: mikeyj001@hotmail.com > CC: wayland-devel@lists.freedesktop.org > > Hi Mike, > > On 25 November 2015 at 16:06, Mike Johnson <mikeyj001@hotmail.com> wrote: > > I've created 2 buffers of the same size (800x600 pixels). So I want the > > input buffer to get filled off-screen, while the output buffer will show the > > content on-screen. > > > > First of all what sort of content could be used to illustrate this > > technique, and secondly, what mechanisms are available to: > > > > a) Notify that the input buffer is full > > b) Copy the content to the output buffer so that it shows on-screen > > It's quite simple. wl_surface_attach(surf, buf) + > wl_surface_commit(surf) will display 'buf' for that surface. At that > point, the compositor owns that buffer, so you should stop drawing on > it. When the compositor has finished with a buffer, it will send you a > wl_buffer.release event. You can sync your paint clock to the > compositor's repaint loop with wl_surface_frame. > > So, the normal workflow is: > - create surface S, buffer A, buffer B > - draw first frame into buffer A > - call wl_surface_frame(S) + wl_surface_attach(S, A) + > wl_surface_commit(S) + wl_display_flush() > - go to sleep > - receive completion for wl_surface_frame callback > - draw second frame into buffer B > - call wl_surface_frame(S) + wl_surface_attach(S, B) + > wl_surface_commit(S) + wl_display_flush() > - compositor now owns both buffers, so don't touch any > - receive wl_buffer.release event for buffer A - now unused > - receive completion for wl_surface_frame callback > - draw third frame into buffer A > - ... > > Hope that helps. You can see the weston-simple-shm client for a pretty > straightforward example. > > Cheers, > Daniel Hi Daniel, Many thanks for the detailed and quick response. You've shown me a couple of functions I hadn't thought of using. I'll give it a go. Kind regards Mike </div> </div></body> </html>