From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dmitry Torokhov Subject: Re: evdev interface question: ABS_X without ABS_Y? Date: Wed, 26 Oct 2011 22:44:12 -0700 Message-ID: <20111027054412.GC15725@core.coreip.homeip.net> References: <8A5EDD26-9BFD-4DAE-9C88-8E8D0908CE8B@patientway.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from mail-gx0-f174.google.com ([209.85.161.174]:43368 "EHLO mail-gx0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751118Ab1J0FoR (ORCPT ); Thu, 27 Oct 2011 01:44:17 -0400 Received: by ggnb1 with SMTP id b1so2311653ggn.19 for ; Wed, 26 Oct 2011 22:44:16 -0700 (PDT) Content-Disposition: inline In-Reply-To: <8A5EDD26-9BFD-4DAE-9C88-8E8D0908CE8B@patientway.com> Sender: linux-input-owner@vger.kernel.org List-Id: linux-input@vger.kernel.org To: Dwayne Litzenberger Cc: linux-input@vger.kernel.org Hi Dwayne, On Wed, Oct 26, 2011 at 05:10:23PM -0400, Dwayne Litzenberger wrote: > I have a quick question about the /dev/input/eventX interface with > userspace. > > Let's say I have a touchscreen, and I move my finger to (200,100). > I'll see something line this (simplified): > > EV_ABS ABS_X 200 > EV_ABS ABS_Y 100 > EV_SYN > > Next, let's say I see something like this: > > EV_ABS ABS_Y 90 > EV_SYN > > What is the meaning of that, from the perspective of userspace? > I see two possibilities. Either: > > 1. It's a move to (200,90), or > 2. It's a move to (0,90) > > Which is the correct interpretation? Door #1. > Is this documented anywhere? >>From Documentation/input/event-codes.txt: "The input protocol is a stateful protocol. Events are emitted only when values of event codes have changed. However, the state is maintained within the Linux input subsystem; drivers do not need to maintain the state and may attempt to emit unchanged values without harm. Userspace may obtain the current state of event code values using the EVIOCG* ioctls defined in linux/input.h." > > Apparently, the usbhid driver is generating events that imply #1, but > xserver-xorg-input-evdev interprets these according to #2. I'm trying > to figure out what needs to be patched. :) xserver-xorg-input-evdev. Thanks. -- Dmitry