pseudo code to confirm how to apply emulation 3rd button code derived from xf86-input-mouse/dist/src/mouse.c to xorg-server/dist/hw/netbsd/x68k (and other DDX) server mouse drivers.

mouse.c

/*
 *
 * Copyright 1990,91 by Thomas Roell, Dinkelscherben, Germany.
 * Copyright 1993 by David Dawes <dawes@xfree86.org>
 * Copyright 2002 by SuSE Linux AG, Author: Egbert Eich
 * Copyright 1994-2002 by The XFree86 Project, Inc.
 * Copyright 2002 by Paul Elliott
 *
 * Permission to use, copy, modify, distribute, and sell this software and its
 * documentation for any purpose is hereby granted without fee, provided that
 * the above copyright notice appear in all copies and that both that
 * copyright notice and this permission notice appear in supporting
 * documentation, and that the names of copyright holders not be
 * used in advertising or publicity pertaining to distribution of the
 * software without specific, written prior permission.  The copyright holders
 * make no representations about the suitability of this
 * software for any purpose.  It is provided "as is" without express or
 * implied warranty.
 *
 * THE COPYRIGHT HOLDERS DISCLAIM ALL WARRANTIES WITH REGARD TO THIS
 * SOFTWARE, INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND
 * FITNESS, IN NO EVENT SHALL THE COPYRIGHT HOLDERS BE LIABLE FOR ANY
 * SPECIAL, INDIRECT OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER
 * RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF
 * CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
 * CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 *
 */

#include "x68k.h"
#include "mi.h"
#include "input.h"
#include "inpututils.h"

#include "exevents.h"
#include "events.h"
#include "eventstr.h"
#include <X11/Xatom.h>
#include "xserver-properties.h"

#ifdef __NetBSD__
#include <time.h>
#include <dev/wscons/wsconsio.h>
#include <sys/ioctl.h>
#endif

static CARD32 buttonTimer(DeviceInfoPtr device);

static void Emulate3ButtonsSetEnabled(DeviceInfoPtr device, Bool enable);
static Bool Emulate3ButtonsSoft(DeviceInfoPtr device);

static void MouseBlockHandler(void *data, void *waitTime);
static void MouseWakeupHandler(void *data, int i);

static void MouseDoPostEvent(DeviceInfoPtr device, int buttons, int dx, int dy);

/**********************************************************************
 *
 *  Emulate3Button support code
 *
 **********************************************************************/


/*
 * Lets create a simple finite-state machine for 3 button emulation:
 *
 * We track buttons 1 and 3 (left and right).  There are 11 states:
 *   0 ground           - initial state
 *   1 delayed left     - left pressed, waiting for right
 *   2 delayed right    - right pressed, waiting for left
 *   3 pressed middle   - right and left pressed, emulated middle sent
 *   4 pressed left     - left pressed and sent
 *   5 pressed right    - right pressed and sent
 *   6 released left    - left released after emulated middle
 *   7 released right   - right released after emulated middle
 *   8 repressed left   - left pressed after released left
 *   9 repressed right  - right pressed after released right
 *  10 pressed both     - both pressed, not emulating middle
 *
 * At each state, we need handlers for the following events
 *   0: no buttons down
 *   1: left button down
 *   2: right button down
 *   3: both buttons down
 *   4: emulate3Timeout passed without a button change
 * Note that button events are not deltas, they are the set of buttons being
 * pressed now.  It's possible (ie, mouse hardware does it) to go from (eg)
 * left down to right down without anything in between, so all cases must be
 * handled.
 *
 * a handler consists of three values:
 *   0: action1
 *   1: action2
 *   2: new emulation state
 *
 * action > 0: ButtonPress
 * action = 0: nothing
 * action < 0: ButtonRelease
 *
 * The comment preceeding each section is the current emulation state.
 * The comments to the right are of the form
 *      <button state> (<events>) -> <new emulation state>
 * which should be read as
 *      If the buttons are in <button state>, generate <events> then go to
 *      <new emulation state>.
 */
static const signed char stateTab[11][5][3] = {
/* 0 ground */
  {
    {  0,  0,  0 },   /* nothing -> ground (no change) */
    {  0,  0,  1 },   /* left -> delayed left */
    {  0,  0,  2 },   /* right -> delayed right */
    {  2,  0,  3 },   /* left & right (middle press) -> pressed middle */
    {  0,  0, -1 }    /* timeout N/A */
  },
/* 1 delayed left */
  {
    {  1, -1,  0 },   /* nothing (left event) -> ground */
    {  0,  0,  1 },   /* left -> delayed left (no change) */
    {  1, -1,  2 },   /* right (left event) -> delayed right */
    {  2,  0,  3 },   /* left & right (middle press) -> pressed middle */
    {  1,  0,  4 },   /* timeout (left press) -> pressed left */
  },
/* 2 delayed right */
  {
    {  3, -3,  0 },   /* nothing (right event) -> ground */
    {  3, -3,  1 },   /* left (right event) -> delayed left (no change) */
    {  0,  0,  2 },   /* right -> delayed right (no change) */
    {  2,  0,  3 },   /* left & right (middle press) -> pressed middle */
    {  3,  0,  5 },   /* timeout (right press) -> pressed right */
  },
/* 3 pressed middle */
  {
    { -2,  0,  0 },   /* nothing (middle release) -> ground */
    {  0,  0,  7 },   /* left -> released right */
    {  0,  0,  6 },   /* right -> released left */
    {  0,  0,  3 },   /* left & right -> pressed middle (no change) */
    {  0,  0, -1 },   /* timeout N/A */
  },
/* 4 pressed left */
  {
    { -1,  0,  0 },   /* nothing (left release) -> ground */
    {  0,  0,  4 },   /* left -> pressed left (no change) */
    { -1,  0,  2 },   /* right (left release) -> delayed right */
    {  3,  0, 10 },   /* left & right (right press) -> pressed both */
    {  0,  0, -1 },   /* timeout N/A */
  },
/* 5 pressed right */
  {
    { -3,  0,  0 },   /* nothing (right release) -> ground */
    { -3,  0,  1 },   /* left (right release) -> delayed left */
    {  0,  0,  5 },   /* right -> pressed right (no change) */
    {  1,  0, 10 },   /* left & right (left press) -> pressed both */
    {  0,  0, -1 },   /* timeout N/A */
  },
/* 6 released left */
  {
    { -2,  0,  0 },   /* nothing (middle release) -> ground */
    { -2,  0,  1 },   /* left (middle release) -> delayed left */
    {  0,  0,  6 },   /* right -> released left (no change) */
    {  1,  0,  8 },   /* left & right (left press) -> repressed left */
    {  0,  0, -1 },   /* timeout N/A */
  },
/* 7 released right */
  {
    { -2,  0,  0 },   /* nothing (middle release) -> ground */
    {  0,  0,  7 },   /* left -> released right (no change) */
    { -2,  0,  2 },   /* right (middle release) -> delayed right */
    {  3,  0,  9 },   /* left & right (right press) -> repressed right */
    {  0,  0, -1 },   /* timeout N/A */
  },
/* 8 repressed left */
  {
    { -2, -1,  0 },   /* nothing (middle release, left release) -> ground */
    { -2,  0,  4 },   /* left (middle release) -> pressed left */
    { -1,  0,  6 },   /* right (left release) -> released left */
    {  0,  0,  8 },   /* left & right -> repressed left (no change) */
    {  0,  0, -1 },   /* timeout N/A */
  },
/* 9 repressed right */
  {
    { -2, -3,  0 },   /* nothing (middle release, right release) -> ground */
    { -3,  0,  7 },   /* left (right release) -> released right */
    { -2,  0,  5 },   /* right (middle release) -> pressed right */
    {  0,  0,  9 },   /* left & right -> repressed right (no change) */
    {  0,  0, -1 },   /* timeout N/A */
  },
/* 10 pressed both */
  {
    { -1, -3,  0 },   /* nothing (left release, right release) -> ground */
    { -3,  0,  4 },   /* left (right release) -> pressed left */
    { -1,  0,  5 },   /* right (left release) -> pressed right */
    {  0,  0, 10 },   /* left & right -> pressed both (no change) */
    {  0,  0, -1 },   /* timeout N/A */
  },
};

static CARD32
buttonTimer(DeviceInfoPtr device)
{
    X68kMousePrivPtr pPriv;
    sigset_t sigmask;
    int id;
    int type, button, flag;
    ValuatorMask mask;

    pPriv = device->public.devicePrivate;

    (void)sigemptyset(&sigmask);
    (void)sigaddset(&sigmask, SIGIO);
    (void)sigprocmask(SIG_BLOCK, &sigmask, NULL);

    pPriv->emulate3Pending = FALSE;
    if ((id = stateTab[pPriv->emulateState][4][0]) != 0) {
        button = abs(id);
        type = (id >= 0) ? ButtonPress : ButtonRelease;
        flag = POINTER_RELATIVE;
        valuator_mask_zero(&mask);
        QueuePointerEvents(device, type, button, flag, &mask);
        pPriv->emulateState = stateTab[pPriv->emulateState][4][2];
    } else {
        LogMessageVerbSigSafe(X_WARNING, -1,
            "Got unexpected buttonTimer in state %d\n", pPriv->emulateState);
    }

    (void)sigprocmask(SIG_UNBLOCK, &sigmask, NULL);
    return 0;
}

static void
Emulate3ButtonsSetEnabled(DeviceInfoPtr device, Bool enable)
{
    X68kMousePrivPtr pPriv = device->public.devicePrivate;

    if (pPriv->emulate3Buttons == enable)
        return;

    pPriv->emulate3Buttons = enable;

    if (enable) {
        pPriv->emulateState = 0;
        pPriv->emulate3Pending = FALSE;
        pPriv->emulate3ButtonsSoft = FALSE; /* specifically requested now */

        RegisterBlockAndWakeupHandlers(MouseBlockHandler, MouseWakeupHandler,
                                       (void *)device);
    } else {
        if (pPriv->emulate3Pending)
            buttonTimer(device);

        RemoveBlockAndWakeupHandlers(MouseBlockHandler, MouseWakeupHandler,
                                     (void *)device);
    }
}

static Bool
Emulate3ButtonsSoft(DeviceInfoPtr device)
{
    X68kMousePrivPtr pPriv;

    pPriv = device->public.devicePrivate;

    if (!pPriv->emulate3ButtonsSoft)
        return TRUE;

#if defined(__NetBSD__) && defined(WSCONS_SUPPORT)
    /*
     * On NetBSD a wsmouse is a multiplexed device. Imagine a notebook
     * with two-button mousepad, and an external USB mouse plugged in
     * temporarily. After using button 3 on the external mouse and
     * unplugging it again, the mousepad will still need to emulate
     * 3 buttons.
     */
    return TRUE;
#else
    LogMessageVerbSigSafe(X_INFO, 4,
        "mouse: 3rd Button detected: disabling emulate3Button\n");

    Emulate3ButtonsSetEnabled(device, FALSE);

    return FALSE;
#endif
}

static void
MouseBlockHandler(void *data, void *waitTime)
{
    DeviceInfoPtr device = data;
    X68kMousePrivPtr pPriv = device->public.devicePrivate;
    int ms;

    if (pPriv->emulate3Pending) {
        ms = pPriv->emulate3Expires - GetTimeInMillis();
        if (ms <= 0)
            ms = 0;
        AdjustWaitForDelay(waitTime, ms);
    }
}

static void
MouseWakeupHandler(void *data, int i)
{
    DeviceInfoPtr device = data;
    X68kMousePrivPtr pPriv = device->public.devicePrivate;
    int ms;

    if (pPriv->emulate3Pending) {
        ms = pPriv->emulate3Expires - GetTimeInMillis();
        if (ms <= 0)
            buttonTimer(device);
    }
}

/*******************************************************************
 *
 * Post mouse events
 *
 *******************************************************************/

static void
MouseDoPostEvent(DeviceInfoPtr device, int buttons, int dx, int dy)
{
    X68kMousePrivPtr pPriv;
    int emulateButtons;
    int id, change;
    int ms;
    int type, button;
    ValuatorMask mask;

    pPriv = device->public.devicePrivate;

    change = buttons ^ pPriv->lastMappedButtons;
    pPriv->lastMappedButtons = buttons;

    if (pPriv->emulate3ButtonsSoft && pPriv->emulate3Pending && (dx || dy))
        buttonTimer(device);

    if (dx || dy) {
        type = MotionNotify;
        flag = POINTER_RELATIVE | POINTER_ACCELERATE;
        valuator[0] = dx;
        valuator[1] = dy;
        valuator_mask_set_range(&mask, 0, 2, valuators);
        QueuePointerEvents(device, type, 0, flag, &mask);
    }

    if (change) {

        if (pPriv->emulate3Buttons
            && (!(buttons & 0x02) || Emulate3ButtonsSoft(device))) {

            /* handle all but buttons 1 & 3 normally */

            change &= ~(0x01 | 0x04);

            /* emulate the third button by the other two */

            emulateButtons = (buttons & 0x01) | ((buttons & 0x04) >> 1);

            if ((id = stateTab[pPriv->emulateState][emulateButtons][0]) != 0) {
                button = abs(id);
                type = (id >= 0) ? ButtonPress : ButtonRelease;
                flag = POINTER_RELATIVE;
                valuator_mask_zero(&mask);
                QueuePointerEvents(device, type, button, flag, &mask);
            }
            if ((id = stateTab[pPriv->emulateState][emulateButtons][1]) != 0) {
                button = abs(id);
                type = (id >= 0) ? ButtonPress : ButtonRelease;
                flag = POINTER_RELATIVE;
                valuator_mask_zero(&mask);
                QueuePointerEvents(device, type, button, flag, &mask);
            }

            pPriv->emulateState =
                stateTab[pPriv->emulateState][emulateButtons][2];

            if (stateTab[pPriv->emulateState][4][0] != 0) {
                pPriv->emulate3Expires =
                    GetTimeInMillis() + pPriv->emulate3Timeout;
                pPriv->emulate3Pending = TRUE;
            } else {
                pPriv->emulate3Pending = FALSE;
            }
        }

        while (change) {
            id = ffs(change);
            change &= ~(1 << (id - 1));
            button = id;
            type = (buttons & (1 << (id - 1))) ? ButtonPress : ButtonRelease;
            flag = POINTER_RELATIVE;
            valuator_mask_zero(&mask);
            QueuePointerEvents(device, type, button, flag, &mask);
        }

    }
}