Add lasso stabilization.

Ported from master branch, commit b4541b4

etc/ipts.conf

@@ -47,5 +47,8 @@
 # Distance = 1600
 
 [Stability]
-## How far an input can move between two frames to be considered stable.
+## How much an input can change in size between two frames to be considered stable.
 # Threshold = 0.1
+
+## How much an input must move between two frames to be considered stable
+# PositionThreshold = 8

src/daemon/config.cpp

@@ -7,6 +7,7 @@
 
 #include <algorithm>
 #include <cctype>
+#include <cmath>
 #include <configure.h>
 #include <filesystem>
 #include <ini.h>
@@ -96,6 +97,12 @@ static int parse_conf(void *user, const char *c_section, const char *c_name, con
 	if (section == "Stability" && name == "Threshold")
 		config->stability_threshold = std::stof(value);
 
+	if (section == "Stability" && name == "PositionThreshold") {
+		config->position_stability_threshold = std::stof(value);
+		config->position_stability_threshold_square =
+			std::pow(config->position_stability_threshold, 2);
+	}
+
 	return 1;
 }
 

src/daemon/config.hpp

@@ -32,6 +32,8 @@ class Config {
 	f32 cone_distance = 1600;
 
 	f32 stability_threshold = 0.1;
+	f32 position_stability_threshold = 8;
+	f64 position_stability_threshold_square = 8 * 8;
 
 	i16 vendor;
 	i16 product;

src/daemon/touch-manager.cpp

@@ -177,6 +177,25 @@ void TouchManager::track()
 					  dev2 < this->conf.stability_threshold) ||
 					 !this->conf.touch_stability;
 
+		f64 dx = this->inputs[i].x - this->last[j].x;
+		f64 dy = this->inputs[i].y - this->last[j].y;
+		f64 sqdist = dx * dx + dy * dy;
+
+		// Is the position stable?
+		if (sqdist < this->conf.position_stability_threshold_square) {
+			this->inputs[i].x = this->last[j].x;
+			this->inputs[i].y = this->last[j].y;
+		} else {
+			f64 dist = std::sqrt(sqdist);
+			f64 x = this->inputs[i].x -
+				this->conf.position_stability_threshold * (dx / dist);
+			f64 y = this->inputs[i].y -
+				this->conf.position_stability_threshold * (dy / dist);
+
+			this->inputs[i].x = gsl::narrow_cast<i32>(x);
+			this->inputs[i].y = gsl::narrow_cast<i32>(y);
+		}
+
 		// Set the distance of all pairs that contain one of i and j
 		// to something even higher than the distance chosen above.
 		// This prevents i and j from getting selected again.