On Tue, 22 Jun 2021 13:02:59 +0900 Esaki Tomohito etom@igel.co.jp 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