From 5858aa055277dbd376c33bb3bbeb6aa74137a17f Mon Sep 17 00:00:00 2001
From: Mikko Rasa <tdb@tdb.fi>
Date: Thu, 19 Nov 2015 23:12:38 +0200
Subject: [PATCH] Refactor GestureDetector and add some comments to it

---
 source/input/gesturedetector.cpp | 137 +++++++++++++++++--------------
 source/input/gesturedetector.h   |   9 +-
 2 files changed, 83 insertions(+), 63 deletions(-)

diff --git a/source/input/gesturedetector.cpp b/source/input/gesturedetector.cpp
index c43e65a..112121e 100644
--- a/source/input/gesturedetector.cpp
+++ b/source/input/gesturedetector.cpp
@@ -54,59 +54,62 @@ string GestureDetector::get_axis_name(unsigned axis) const
 
 void GestureDetector::touch_down(unsigned btn)
 {
-	if(btn<3)
-	{
-		TouchPoint &p = points[btn];
-		p.down = true;
-		p.down_x = p.x;
-		p.down_y = p.y;
-	}
+	if(btn>=MAX_POINTS)
+		return;
+
+	TouchPoint &p = points[btn];
+	p.down = true;
+	p.down_x = p.x;
+	p.down_y = p.y;
+	p.x = 0;
+	p.y = 0;
+	p.threshold_exceeded = false;
 }
 
 void GestureDetector::touch_up(unsigned btn)
 {
-	if(btn<3)
-	{
-		TouchPoint &p = points[btn];
-		p.down = false;
+	if(btn>=MAX_POINTS)
+		return;
 
-		if(active_points&(1<<btn))
-		{
-			set_button_state(current_gesture, false, true);
-			set_axis_value(2, 0, false);
-			current_gesture = GESTURE_NONE;
-			active_points = 0;
-			invalid_gesture = true;
-		}
+	TouchPoint &p = points[btn];
+	p.x += p.down_x;
+	p.y += p.down_y;
+	p.down = false;
 
-		if(invalid_gesture)
-		{
-			invalid_gesture = false;
-			for(unsigned i=0; i<3; ++i)
-				if(points[i].down)
-					invalid_gesture = true;
-		}
+	if(active_points&(1<<btn))
+		end_gesture();
+
+	if(current_gesture==GESTURE_NONE)
+	{
+		// New gesture can't start until all points have been released.
+		invalid_gesture = false;
+		for(unsigned i=0; (i<MAX_POINTS && !invalid_gesture); ++i)
+			invalid_gesture = points[i].down;
 	}
 }
 
 void GestureDetector::touch_move(unsigned axis, float value, float)
 {
-	if(axis<6)
+	if(axis>=MAX_POINTS*2)
+		return;
+
+	unsigned i = axis>>1;
+	TouchPoint &p = points[i];
+	// Track relative position when pressed, absolute when not.
+	if(axis&1)
+		p.y = (p.down ? value-p.down_y : value);
+	else
+		p.x = (p.down ? value-p.down_x : value);
+
+	if(p.down)
 	{
-		unsigned i = axis>>1;
-		TouchPoint &p = points[i];
-		if(axis&1)
-			p.y = value;
-		else
-			p.x = value;
+		if(p.x*p.x/threshold_x_sq+p.y*p.y/threshold_y_sq>=1)
+			p.threshold_exceeded = true;
 
-		if(p.down)
-		{
-			if(current_gesture==GESTURE_NONE && !invalid_gesture)
-				start_gesture();
-			else if(active_points&(1<<i))
-				update_progress();
-		}
+		if(current_gesture==GESTURE_NONE && !invalid_gesture)
+			start_gesture();
+		else if(active_points&(1<<i))
+			update_progress();
 	}
 }
 
@@ -116,47 +119,47 @@ void GestureDetector::start_gesture()
 	if(!p.down)
 		return;
 
-	float dx = p.x-p.down_x;
-	float dy = p.y-p.down_y;
-	if(dx*dx/threshold_x_sq+dy*dy/threshold_y_sq<1)
+	/* At least one point needs to have moved more than the threshold to start
+	the gesture. */
+	bool threshold_exceeded = false;
+	for(unsigned i=0; (i<MAX_POINTS && !threshold_exceeded); ++i)
+		threshold_exceeded = (points[i].down && points[i].threshold_exceeded);
+	if(!threshold_exceeded)
 		return;
 
 	invalid_gesture = false;
 	if(points[1].down)
 	{
 		TouchPoint &p2 = points[1];
-		float dx2 = p2.x-p2.down_x;
-		float dy2 = p2.y-p2.down_y;
 		float ddx = p.down_x-p2.down_x;
 		float ddy = p.down_y-p2.down_y;
-		/* TODO Should the second point be also required to exceeded the
-		threshold? */
-		if(dx*dx2+dy*dy2<0 && (dx*ddx+dy*ddy)*(dx2*ddx+dy2*ddy)<0)
-		{
+		if(p.x*p2.x+p.y*p2.y<0 && (p.x*ddx+p.y*ddy)*(p2.x*ddx+p2.y*ddy)<0)
+			/* If the points moved in different directions and also both away from
+			or towards the other, it's a pinch gesture. */
 			current_gesture = GESTURE_PINCH;
-			active_points = 3;
-		}
 		else
 			invalid_gesture = true;
 
 		if(current_gesture!=GESTURE_NONE)
 		{
+			active_points = 3;
 			set_axis_value(0, (p.down_x+p2.down_x)/2, true);
 			set_axis_value(1, (p.down_y+p2.down_y)/2, true);
 		}
 	}
 	else
 	{
-		active_points = 1;
-		if(abs(dx)>2*abs(dy))
-			current_gesture = (dx>0 ? GESTURE_SWIPE_RIGHT : GESTURE_SWIPE_LEFT);
-		else if(abs(dy)>2*abs(dx))
-			current_gesture = (dy>0 ? GESTURE_SWIPE_UP : GESTURE_SWIPE_DOWN);
+		// Allow a maximum deviation of about 26° to recognize a swipe gesture.
+		if(abs(p.x)>2*abs(p.y))
+			current_gesture = (p.x>0 ? GESTURE_SWIPE_RIGHT : GESTURE_SWIPE_LEFT);
+		else if(abs(p.y)>2*abs(p.x))
+			current_gesture = (p.y>0 ? GESTURE_SWIPE_UP : GESTURE_SWIPE_DOWN);
 		else
 			invalid_gesture = true;
 
 		if(current_gesture!=GESTURE_NONE)
 		{
+			active_points = 1;
 			set_axis_value(0, p.down_x, true);
 			set_axis_value(1, p.down_y, true);
 		}
@@ -173,24 +176,34 @@ void GestureDetector::update_progress()
 	TouchPoint &p = points[0];
 
 	if(current_gesture==GESTURE_SWIPE_DOWN)
-		set_axis_value(2, p.down_y-p.y, true);
+		set_axis_value(2, -p.y, true);
 	else if(current_gesture==GESTURE_SWIPE_UP)
-		set_axis_value(2, p.y-p.down_y, true);
+		set_axis_value(2, p.y, true);
 	else if(current_gesture==GESTURE_SWIPE_LEFT)
-		set_axis_value(2, p.down_x-p.x, true);
+		set_axis_value(2, -p.x, true);
 	else if(current_gesture==GESTURE_SWIPE_RIGHT)
-		set_axis_value(2, p.x-p.down_x, true);
+		set_axis_value(2, p.x, true);
 	else if(current_gesture==GESTURE_PINCH)
 	{
 		TouchPoint &p2 = points[1];
-		float dx = p.x-p2.x;
-		float dy = p.y-p2.y;
+		/* Pinch progress is the ratio between the current distance of the points
+		and their distance when they were pressed. */
 		float ddx = p.down_x-p2.down_x;
 		float ddy = p.down_y-p2.down_y;
+		float dx = ddx+p.x-p2.x;
+		float dy = ddy+p.y-p2.y;
 		set_axis_value(2, sqrt(dx*dx+dy*dy)/sqrt(ddx*ddx+ddy*ddy)-1, true);
 	}
 }
 
+void GestureDetector::end_gesture()
+{
+	set_button_state(current_gesture, false, true);
+	set_axis_value(2, 0, false);
+	current_gesture = GESTURE_NONE;
+	active_points = 0;
+}
+
 void GestureDetector::window_resized(unsigned w, unsigned h)
 {
 	threshold_x_sq = 2500.0/(w*w);
diff --git a/source/input/gesturedetector.h b/source/input/gesturedetector.h
index 2b5ea3c..b2d0d4f 100644
--- a/source/input/gesturedetector.h
+++ b/source/input/gesturedetector.h
@@ -27,6 +27,11 @@ absolute values greater than one.
 class GestureDetector: public Device
 {
 private:
+	enum
+	{
+		MAX_POINTS = 3
+	};
+
 	struct TouchPoint
 	{
 		bool down;
@@ -34,12 +39,13 @@ private:
 		float down_y;
 		float x;
 		float y;
+		bool threshold_exceeded;
 
 		TouchPoint();
 	};
 
 	Touchscreen &touchscreen;
-	TouchPoint points[3];
+	TouchPoint points[MAX_POINTS];
 	Gesture current_gesture;
 	unsigned active_points;
 	bool invalid_gesture;
@@ -58,6 +64,7 @@ private:
 	void touch_move(unsigned, float, float);
 	void start_gesture();
 	void update_progress();
+	void end_gesture();
 	void window_resized(unsigned, unsigned);
 };
 
-- 
2.43.0