On Tue, 22 Jun 2021 13:02:59 +0900 Esaki Tomohito <etom@xxxxxxxxxx> wrote: > Hi, Thomas > Thank you for reply. > > On 2021/06/21 16:10, Thomas Zimmermann wrote: > > Hi > > > > Am 21.06.21 um 08:27 schrieb Tomohito Esaki: > >> Virtual DRM splits the overlay planes of a display controller into > >> multiple > >> virtual devices to allow each plane to be accessed by each process. > >> > >> This makes it possible to overlay images output from multiple > >> processes on a > >> display. For example, one process displays the camera image without > >> compositor > >> while another process overlays the UI. > > > > I briefly looked over your patches. I didn't understand how this is > > different to the functionality of a compositor? Shouldn't this be solved > > in userspace? > > I think when latency is important (e.g., AR, VR, for displaying camera > images in IVI systems), there may be use cases where the compositor > cannot be used. Hi, > Normally, when the image is passed through the compositor, it is > displayed after 2 VSYNC at most, because the compositor combines the > image with VSYNC synchronization. This is not a universal fact. You can write a Wayland compositor that consistently reaches app-to-screen latency of less than one monitor refresh cycle, while also using KMS planes. I believe Weston succeeds in this already if you write the Wayland application accordingly. Thanks, pq
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