On Thu, May 21, 2020 at 07:42:33PM +0900, 강정현 wrote: > Dear all, > > I have an one question about Linux MT Protocol B type. > > Asume that press touch screen using first finger. > > And release fisrt finger and press second finger toghether. > > > > In that case, which procotol is correct? > > ┌───────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐ > │ ABS_MT_SLOT 0 > │ > │ > │ > │ ABS_MT_TRACKING_ID 1 > │ > │ > │ > │ ABS_MT_POSITION_X 10 > │ > │ > │ > │ ABS_MT_POSITION_Y 5 > │ > │ > │ > │ ABS_MT_SYNC <-- first finger press > │ > └───────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
There's no such thing as ABS_MT_SYNC, use SYN_REPORT here. > first case > > ┌───────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐ > │ ABS_MT_TRACKING_ID -1 > │ > │ > │ > │ ABS_MT_TRACKING_ID 2 > │ > │ > │ > │ ABS_MT_POSITION_X 15 > │ > │ > │ > │ ABS_MT_POSITION_Y 10 > │ > │ > │ > │ ABS_MT_SYNC <-- first finger release and first finger press is generated > │ > └───────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘ Nope, that's wrong. You could skip the tracking ID -1 event and switch directly to ID 2. This is technically allowed by the protocol but a lot of userspace (anything Xorg and libinput) will struggle with it for historical reasons. Where you are re-using the same slot, you should always stop a touch and start the next touch in a separate frame. Direct switching also introduces some ambiguity because it merely means "kernel lost tracking of touch point", so userspace now has to decide whether it's the same touch or a new touch. > > second case > > ┌────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐ > │ ABS_MT_TRACKING_ID -1 > │ > │ > │ > │ ABS_MT_SLOT 1 > │ > │ > │ > │ ABS_MT_TRACKING_ID 2 > │ > │ > │ > │ ABS_MT_POSITION_X 15 > │ > │ > │ > │ ABS_MT_POSITION_Y 10 > │ > │ > │ > │ ABS_MT_SYNC <-- first finger release and second finger press is generated > │ > └────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘ this is the correct sequence (except for the ABS_MT_SYNC bit :). Cheers, Peter _______________________________________________ wayland-devel mailing list wayland-devel@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/wayland-devel
