Add drag lock support

First, why is this here and not in libinput: drag lock should be implemented
in the compositor (not in libinput) so it can provide feedback when it
activates and grouped in with other accessibility features. That will work for
Wayland but in X the compositor cannot filter button events - only the server
and the drivers can.

This patch adds mostly the same functionality that evdev provides with two
options on how it works:
* a single button number configures the given button to lock the next button
  pressed in a logically down state until a press+ release of that same button
  again
* a set of button number pairs configures each button with the to-be-locked
  logical button, i.e. a pair of "1 3" will hold 3 logically down after a
  button 1 press

The property and the xorg.conf options take the same configuration as the
evdev driver (though the property has a different prefix, libinput instead of
Evdev).

The behavior difference to evdev is in how releases are handled, evdev sends
the release on the second button press event, this implementation sends the
release on the second release event.

https://bugs.freedesktop.org/show_bug.cgi?id=85577

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>

1 files changed, 282 insertions, 0 deletions

diff --git a/src/draglock.c b/src/draglock.c
new file mode 100644
index 0000000..b0bcac3
--- /dev/null
+++ b/src/draglock.c
@@ -0,0 +1,282 @@
+/*
+ * Copyright © 2015 Red Hat, Inc.
+ *
+ * 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 name of Red Hat
+ * not be used in advertising or publicity pertaining to distribution
+ * of the software without specific, written prior permission.  Red
+ * Hat makes no representations about the suitability of this software
+ * for any purpose.  It is provided "as is" without express or implied
+ * warranty.
+ *
+ * THE AUTHORS DISCLAIM ALL WARRANTIES WITH REGARD TO THIS SOFTWARE,
+ * INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS, IN
+ * NO EVENT SHALL THE AUTHORS 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.
+ */
+
+#ifdef HAVE_CONFIG_H
+#include "config.h"
+#endif
+
+#include "draglock.h"
+
+#include <string.h>
+#include <stdlib.h>
+
+#define ARRAY_SIZE(a) (sizeof(a)/sizeof((a)[0]))
+
+static int
+draglock_parse_config(struct draglock *dl, const char *config)
+{
+    int button = 0, target = 0;
+    const char *str = NULL;
+    char *end_str = NULL;
+    int pairs[DRAGLOCK_MAX_BUTTONS] = {0};
+
+    if (!config)
+	    return 0;
+
+    /* empty string disables drag lock */
+    if (*config == '\0') {
+	    dl->mode = DRAGLOCK_DISABLED;
+	    return 0;
+    }
+
+    /* check for a single-number string first, config is "<int>" */
+    button = strtol(config, &end_str, 10);
+    if (*end_str == '\0') {
+	    if (button < 0 || button >= DRAGLOCK_MAX_BUTTONS)
+		    return 1;
+	    /* we allow for button 0 so stacked xorg.conf.d snippets can
+	     * disable the config again */
+	    if (button == 0) {
+		    dl->mode = DRAGLOCK_DISABLED;
+		    return 0;
+	    }
+
+	    return draglock_set_meta(dl, button);
+    }
+
+    dl->mode = DRAGLOCK_DISABLED;
+
+    /* check for a set of button pairs, config is
+     * "<int> <int> <int> <int>..." */
+    str = config;
+    while (*str != '\0') {
+	    button = strtol(str, &end_str, 10);
+	    if (*end_str == '\0')
+		    return 1;
+
+	    str = end_str;
+	    target = strtol(str, &end_str, 10);
+	    if (end_str == str)
+		    return 1;
+	    if (button <= 0 || button >= DRAGLOCK_MAX_BUTTONS || target >= DRAGLOCK_MAX_BUTTONS)
+		    return 1;
+
+	    pairs[button] = target;
+	    str = end_str;
+    }
+
+    return draglock_set_pairs(dl, pairs, ARRAY_SIZE(pairs));
+}
+
+int
+draglock_init_from_string(struct draglock *dl, const char *config)
+{
+	dl->mode = DRAGLOCK_DISABLED;
+
+	dl->meta_button = 0;
+	dl->meta_state = false;
+	memset(dl->lock_pair, 0, sizeof(dl->lock_pair));
+	memset(dl->lock_state, 0, sizeof(dl->lock_state));
+
+	return draglock_parse_config(dl, config);
+}
+
+enum draglock_mode
+draglock_get_mode(const struct draglock *dl)
+{
+	return dl->mode;
+}
+
+int
+draglock_get_meta(const struct draglock *dl)
+{
+	if (dl->mode == DRAGLOCK_META)
+		return dl->meta_button;
+	return 0;
+}
+
+size_t
+draglock_get_pairs(const struct draglock *dl, int *array, size_t sz)
+{
+	unsigned int i;
+	size_t last = 0;
+
+	if (dl->mode != DRAGLOCK_PAIRS)
+		return 0;
+
+	/* size 1 array with the meta button */
+	if (dl->meta_button) {
+		*array = dl->meta_button;
+		return 1;
+	}
+
+	/* size N array with a[0] == 0, the rest ordered by button number */
+	memset(array, 0, sz * sizeof(array[0]));
+	for (i = 0; i < sz && i < ARRAY_SIZE(dl->lock_pair); i++) {
+		array[i] = dl->lock_pair[i];
+		if (array[i] != 0 && i > last)
+			last = i;
+	}
+	return last;
+}
+
+int
+draglock_set_meta(struct draglock *dl, int meta_button)
+{
+	if (meta_button < 0 || meta_button >= DRAGLOCK_MAX_BUTTONS)
+		return 1;
+
+	dl->meta_button = meta_button;
+	dl->mode = meta_button ? DRAGLOCK_META : DRAGLOCK_DISABLED;
+
+	return 0;
+}
+
+int
+draglock_set_pairs(struct draglock *dl, const int *array, size_t sz)
+{
+	unsigned int i;
+
+	if (sz == 0 || array[0] != 0)
+		return 1;
+
+	for (i = 0; i < sz; i++) {
+		if (array[i] < 0 || array[i] >= DRAGLOCK_MAX_BUTTONS)
+			return 1;
+	}
+
+	dl->mode = DRAGLOCK_DISABLED;
+	for (i = 0; i < sz; i++) {
+		dl->lock_pair[i] = array[i];
+		if (dl->lock_pair[i])
+			dl->mode = DRAGLOCK_PAIRS;
+	}
+
+	return 0;
+}
+
+static int
+draglock_filter_meta(struct draglock *dl, int *button, int *press)
+{
+	int b = *button,
+	    is_press = *press;
+
+	if (b == dl->meta_button) {
+		if (is_press)
+			dl->meta_state = true;
+		*button = 0;
+		return 0;
+	}
+
+	switch (dl->lock_state[b]) {
+	case DRAGLOCK_BUTTON_STATE_NONE:
+		if (dl->meta_state && is_press) {
+			dl->lock_state[b] = DRAGLOCK_BUTTON_STATE_DOWN_1;
+			dl->meta_state = false;
+		}
+		break;
+	case DRAGLOCK_BUTTON_STATE_DOWN_1:
+		if (!is_press) {
+			dl->lock_state[b] = DRAGLOCK_BUTTON_STATE_UP_1;
+			b = 0;
+		}
+		break;
+	case DRAGLOCK_BUTTON_STATE_UP_1:
+		if (is_press) {
+			dl->lock_state[b] = DRAGLOCK_BUTTON_STATE_DOWN_2;
+			b = 0;
+		}
+		break;
+	case DRAGLOCK_BUTTON_STATE_DOWN_2:
+		if (!is_press) {
+			dl->lock_state[b] = DRAGLOCK_BUTTON_STATE_NONE;
+		}
+		break;
+	}
+
+	*button = b;
+
+	return 0;
+}
+
+static int
+draglock_filter_pair(struct draglock *dl, int *button, int *press)
+{
+	int b = *button,
+	    is_press = *press;
+
+	if (dl->lock_pair[b] == 0)
+		return 0;
+
+	switch (dl->lock_state[b]) {
+	case DRAGLOCK_BUTTON_STATE_NONE:
+		if (is_press) {
+			dl->lock_state[b] = DRAGLOCK_BUTTON_STATE_DOWN_1;
+			b = dl->lock_pair[b];
+		}
+		break;
+	case DRAGLOCK_BUTTON_STATE_DOWN_1:
+		if (!is_press) {
+			dl->lock_state[b] = DRAGLOCK_BUTTON_STATE_UP_1;
+			b = 0;
+		}
+		break;
+	case DRAGLOCK_BUTTON_STATE_UP_1:
+		if (is_press) {
+			dl->lock_state[b] = DRAGLOCK_BUTTON_STATE_DOWN_2;
+			b = 0;
+		}
+		break;
+	case DRAGLOCK_BUTTON_STATE_DOWN_2:
+		if (!is_press) {
+			dl->lock_state[b] = DRAGLOCK_BUTTON_STATE_NONE;
+			b = dl->lock_pair[b];
+		}
+		break;
+	}
+
+	*button = b;
+
+	return 0;
+}
+
+int
+draglock_filter_button(struct draglock *dl, int *button, int *is_press)
+{
+	if (*button == 0)
+		return 0;
+
+	switch(dl->mode) {
+	case DRAGLOCK_DISABLED:
+		return 0;
+	case DRAGLOCK_META:
+		return draglock_filter_meta(dl, button, is_press);
+	case DRAGLOCK_PAIRS:
+		return draglock_filter_pair(dl, button, is_press);
+	default:
+		abort();
+		break;
+	}
+
+	return 0;
+}