borrwoed a lot code from https://github.com/foriequal0/devterm_keyboard in order to optimize the trackball

Code/devterm_keyboard/glider.ino

@@ -0,0 +1,60 @@
+#include <cmath>
+
+#include "glider.h"
+#include "math.h"
+
+Glider::Glider()
+: speed(0),
+  sustain(0),
+  release(0),
+  error(0)
+{}
+
+void Glider::setDirection(int8_t direction) {
+  if (this->direction != direction) {
+    stop();
+  }
+  this->direction = direction;
+}
+
+void Glider::update(float speed, uint16_t sustain) {
+  this->speed = speed;
+  this->sustain = sustain;
+  this->release = sustain;
+}
+
+void Glider::updateSpeed(float speed) {
+  this->speed = speed;
+}
+
+void Glider::stop() {
+  this->speed = 0;
+  this->sustain = 0;
+  this->release = 0;
+  this->error = 0;
+}
+
+Glider::GlideResult Glider::glide(millis_t delta) {
+  const auto alreadyStopped = speed == 0;
+
+  error += speed * delta;
+  int8_t distance = 0;
+  if (error > 0) {
+    distance = clamp<int8_t>(std::ceil(error));
+  }
+  error -= distance;
+
+  if (sustain > 0) {
+    const auto sustained = min(sustain, (uint16_t)delta);
+    sustain -= sustained;
+  } else if (release > 0) {
+    const auto released = min(release, (uint16_t)delta);
+    speed = speed * (release - released) / release;
+    release -= released;
+  } else {
+    speed = 0;
+  }
+
+  const int8_t result = direction * distance;
+  return GlideResult { result, !alreadyStopped && speed == 0 };
+}