touchscreen: Add gesture recognition API

Add a basic gesture API which can detect taps, long presses,
and dragging gestures.

Change-Id: Id10bf8d46b9195330ce951f9f108c81e87a8dad4

apps/gesture.h

@@ -0,0 +1,123 @@
+/***************************************************************************
+ *             __________               __   ___.
+ *   Open      \______   \ ____   ____ |  | _\_ |__   _______  ___
+ *   Source     |       _//  _ \_/ ___\|  |/ /| __ \ /  _ \  \/  /
+ *   Jukebox    |    |   (  <_> )  \___|    < | \_\ (  <_> > <  <
+ *   Firmware   |____|_  /\____/ \___  >__|_ \|___  /\____/__/\_ \
+ *                     \/            \/     \/    \/            \/
+ * $Id$
+ *
+ * Copyright (C) 2022 Aidan MacDonald
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
+ * KIND, either express or implied.
+ *
+ ****************************************************************************/
+#ifndef _GESTURE_H_
+#define _GESTURE_H_
+
+#include <stddef.h>
+#include <stdbool.h>
+
+struct viewport;
+struct touchevent;
+
+/** Events which can be detected by the gesture API.
+ *
+ * The gesture state machine, informally, looks like this:
+ *
+ *     NONE --+--> TAP ------------------------------------+
+ *            |                                            |
+ *            +--> LONG_PRESS -----------------------------+
+ *            |             |                              |
+ *            |             +---> HOLD ---+                |
+ *            |             |             |                |
+ *            +-------------+---> DRAG ---+--> RELEASE ----+--> NONE
+ *
+ * State transitions occur from gesture_process() in response to touch events.
+ *
+ * - The NONE "event" is returned prior to any other gesture being detected.
+ *   Although the graph above depicts a transition back to NONE at the end of
+ *   an event chain, that transition in fact happens on the TOUCHEVENT_PRESS
+ *   after the end of the last event.
+ *
+ * - TAP events are reported after getting a TOUCHEVENT_RELEASE event if no
+ *   other gestures were detected between the press and release.
+ *
+ * - LONG_PRESS events are reported on a TOUCHEVENT_CONTACT event if the long
+ *   press timeout has expired and the touch point hasn't moved too far from
+ *   its initial position.
+ *
+ * - HOLD events are reported on TOUCHEVENT_CONTACT events after a LONG_PRESS,
+ *   provided the touch point hasn't moved too far from its initial position.
+ *
+ * - DRAG events are reported on TOUCHEVENT_CONTACT events after the touch
+ *   point first moves a certain distance from its initial position. The first
+ *   time this happens, it is reported as DRAGSTART.
+ *
+ * - RELEASE events are reported on the TOUCHEVENT_RELEASE event following a
+ *   HOLD or DRAG gesture.
+ */
+enum gesture_id
+{
+    GESTURE_NONE = 0,       /** No gesture */
+    GESTURE_TAP,            /** Quick press & release */
+    GESTURE_LONG_PRESS,     /** Start of a long press */
+    GESTURE_HOLD,           /** Continuation of a long press */
+    GESTURE_DRAGSTART,      /** Start of a DRAG event */
+    GESTURE_DRAG,           /** Press and drag on the screen */
+    GESTURE_RELEASE,        /** End of a HOLD or DRAG event */
+};
+
+enum gesture_flags
+{
+    GESTURE_F_VALID = 0x01,
+    GESTURE_F_PRESSED = 0x02,
+};
+
+struct gesture
+{
+    unsigned int flags;
+    int id;
+    short x, y;
+    short ox, oy;
+    long start_tick;
+    long last_tick;
+};
+
+struct gesture_event
+{
+    int id;
+    short x, y;
+    short ox, oy;
+    long start_tick;
+    long last_tick;
+};
+
+void gesture_reset(struct gesture *g);
+void gesture_process(struct gesture *g, const struct touchevent *ev);
+bool gesture_get_event_in_vp(struct gesture *g, struct gesture_event *gevt,
+                             const struct viewport *vp);
+
+static inline bool gesture_get_event(struct gesture *g,
+                                     struct gesture_event *gevt)
+{
+    return gesture_get_event_in_vp(g, gevt, NULL);
+}
+
+static inline bool gesture_is_valid(struct gesture *g)
+{
+    return !!(g->flags & GESTURE_F_VALID);
+}
+
+static inline bool gesture_is_pressed(struct gesture *g)
+{
+    return !!(g->flags & GESTURE_F_PRESSED);
+}
+
+#endif /* _GESTURE_H_ */