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diff --git a/src/draglock.h b/src/draglock.h
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+/*
+ * 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
+
+#ifndef DRAGLOCK_H
+#define DRAGLOCK_H 1
+
+#include <stdbool.h>
+#include <stdlib.h>
+
+/* 32 buttons are enough for everybody™
+ * Note that this is the limit of physical buttons as well as the highest
+ * allowed target button.
+ */
+#define DRAGLOCK_MAX_BUTTONS 32
+
+enum draglock_mode
+{
+	DRAGLOCK_DISABLED,
+	DRAGLOCK_META,
+	DRAGLOCK_PAIRS
+};
+
+enum draglock_button_state
+{
+	DRAGLOCK_BUTTON_STATE_NONE,
+	DRAGLOCK_BUTTON_STATE_DOWN_1,
+	DRAGLOCK_BUTTON_STATE_UP_1,
+	DRAGLOCK_BUTTON_STATE_DOWN_2,
+};
+
+struct draglock
+{
+	enum draglock_mode mode;
+	int meta_button;			/* meta key to lock any button */
+	bool meta_state;			/* meta_button state */
+	unsigned int lock_pair[DRAGLOCK_MAX_BUTTONS + 1];/* specify a meta/lock pair */
+	enum draglock_button_state lock_state[DRAGLOCK_MAX_BUTTONS + 1];	/* state of any locked buttons */
+};
+
+/**
+ * Initialize the draglock struct based on the config string. The string is
+ * either a single number to configure DRAGLOCK_META mode or a list of
+ * number pairs, with pair[0] as button and pair[1] as target lock number to
+ * configure DRAGLOCK_PAIRS mode.
+ *
+ * If config is NULL, the empty string, "0" or an even-numbered list of 0,
+ * the drag lock mode is DRAGLOCK_DISABLED.
+ *
+ * @return 0 on success or nonzero on error
+ */
+int
+draglock_init_from_string(struct draglock *dl, const char *config);
+
+/**
+ * Get the current drag lock mode.
+ *
+ * If the mode is DRAGLOCK_META, a meta button click will cause the next
+ * subsequent button click to be held logically down until the release of
+ * the second button click of that same button. Events from the meta button
+ * are always discarded.
+ *
+ * If the mode is DRAGLOCK_PAIRS, any button may be configured with a
+ * 'target' button number. A click of that button causes the target button
+ * to be held logically down until the release of the second button click.
+ */
+enum draglock_mode
+draglock_get_mode(const struct draglock *dl);
+
+/**
+ * @return the meta button number or 0 if the current mode is not
+ * DRAGLOCK_META.
+ */
+int
+draglock_get_meta(const struct draglock *dl);
+
+/**
+ * Get the drag lock button mapping pairs. The array is filled with the
+ * button number as index and the mapped target button number as value, i.e.
+ * array[3] == 8 means button 3 will draglock button 8.
+ *
+ * A value of 0 indicates draglock is disabled for that button.
+ *
+ * @note Button numbers start at 1, array[0] is always 0.
+ *
+ * @param[in|out] array Caller-allocated array to hold the button mappings.
+ * @param[in] nelem Maximum number of elements in array
+ *
+ * @return The number of valid elements in array or 0 if the current mode is
+ * not DRAGLOCK_PAIRS
+ */
+size_t
+draglock_get_pairs(const struct draglock *dl, int *array, size_t nelem);
+
+/**
+ * Set the drag lock config to the DRAGLOCK_META mode, with the given
+ * button as meta button.
+ *
+ * If the button is 0 the mode becomes DRAGLOCK_DISABLED.
+ *
+ * @return 0 on success, nonzero otherwise
+ */
+int
+draglock_set_meta(struct draglock *dl, int meta_button);
+
+/**
+ * Set the drag lock config to the DRAGLOCK_PAIRS mode. The array
+ * must be filled with the button number as index and the mapped target
+ * button number as value, i.e.
+ * array[3] == 8 means button 3 will draglock button 8.
+ *
+ * A value of 0 indicates draglock is disabled for that button. If all
+ * buttons are 0, the mode becomes DRAGLOCK_DISABLED.
+ *
+ * @note Button numbers start at 1, array[0] is always 0.
+ *
+ * @return 0 on successor nonzero otherwise
+ */
+int
+draglock_set_pairs(struct draglock *dl, const int *array, size_t nelem);
+
+/**
+ * Process the given button event through the drag lock state machine.
+ * If the event is to be discarded by the caller, button is set to 0.
+ * Otherwise, button is set to the button event to process and is_press is
+ * set to the button state to process.
+ *
+ * @param[in|out] button The button number to process
+ * @param[in|out] is_press nonzero for press, zero for release
+ *
+ * @return 0 on success or 1 on error
+ */
+int
+draglock_filter_button(struct draglock *dl, int *button, int *is_press);
+
+#endif /* DRAGLOCK_H */