Implement kinetic mouse movement algorithm (#6739)

* Implement kinetic mouse movement algorithm

* Adjust mouse wheel speed

* Remove unused math.h include

* Wrap mouse_timer definition in ifdef

* Replace double space by single space

* Clarify documentation of kinetic mouse speed

Co-Authored-By: lf <software@lfcode.ca>

* Clarify documentation of kinetic mouse speed

Co-Authored-By: lf <software@lfcode.ca>

* Remove superfluous definition of speed

* fix(variable): remove unused variable

Co-authored-by: lf <software@lfcode.ca>

2 files changed, 117 insertions, 2 deletions

diff --git a/tmk_core/common/mousekey.c b/tmk_core/common/mousekey.c
index ef18bcf1a8..697e0692c0 100644
--- a/tmk_core/common/mousekey.c
+++ b/tmk_core/common/mousekey.c
@@ -36,6 +36,9 @@ static void           mousekey_debug(void);
 static uint8_t        mousekey_accel        = 0;
 static uint8_t        mousekey_repeat       = 0;
 static uint8_t        mousekey_wheel_repeat = 0;
+#ifdef MK_KINETIC_SPEED
+static uint16_t       mouse_timer     = 0;
+#endif
 
 #ifndef MK_3_SPEED
 
@@ -43,7 +46,7 @@ static uint16_t last_timer_c = 0;
 static uint16_t last_timer_w = 0;
 
 /*
- * Mouse keys  acceleration algorithm
+ * Mouse keys acceleration algorithm
  *  http://en.wikipedia.org/wiki/Mouse_keys
  *
  *  speed = delta * max_speed * (repeat / time_to_max)**((1000+curve)/1000)
@@ -105,6 +108,69 @@ static uint8_t wheel_unit(void) {
 }
 
 #    else /* #ifndef MK_COMBINED */
+#        ifndef MK_KINETIC_SPEED
+
+/*
+ * Kinetic movement  acceleration algorithm
+ *
+ *  current speed = I + A * T/50 + A * 0.5 * T^2 | maximum B
+ *
+ * T: time since the mouse movement started
+ * E: mouse events per second (set through MOUSEKEY_INTERVAL, UHK sends 250, the
+ *    pro micro on my Signum 3.0 sends only 125!)
+ * I: initial speed at time 0
+ * A: acceleration
+ * B: base mouse travel speed
+ */
+const uint16_t mk_accelerated_speed = MOUSEKEY_ACCELERATED_SPEED;
+const uint16_t mk_base_speed = MOUSEKEY_BASE_SPEED;
+const uint16_t mk_decelerated_speed = MOUSEKEY_DECELERATED_SPEED;
+const uint16_t mk_initial_speed = MOUSEKEY_INITIAL_SPEED;
+
+static uint8_t move_unit(void) {
+    float speed = mk_initial_speed;
+
+    if (mousekey_accel & ((1<<0) | (1<<2))) {
+        speed = mousekey_accel & (1<<2) ? mk_accelerated_speed : mk_decelerated_speed;
+    } else if (mousekey_repeat && mouse_timer) {
+        const float time_elapsed = timer_elapsed(mouse_timer) / 50;
+        speed = mk_initial_speed +
+            MOUSEKEY_MOVE_DELTA * time_elapsed +
+            MOUSEKEY_MOVE_DELTA * 0.5 * time_elapsed * time_elapsed;
+
+        speed = speed > mk_base_speed ? mk_base_speed : speed;
+    }
+
+    /* convert speed to USB mouse speed 1 to 127 */
+    speed = (uint8_t)(speed / (1000.0f / mk_interval));
+    speed = speed < 1 ? 1 : speed;
+
+    return speed > MOUSEKEY_MOVE_MAX ? MOUSEKEY_MOVE_MAX : speed;
+}
+
+float mk_wheel_interval = 1000.0f / MOUSEKEY_WHEEL_INITIAL_MOVEMENTS;
+
+static uint8_t wheel_unit(void) {
+    float speed = MOUSEKEY_WHEEL_INITIAL_MOVEMENTS;
+
+    if (mousekey_accel & ((1<<0) | (1<<2))) {
+        speed = mousekey_accel & (1<<2) ? MOUSEKEY_WHEEL_ACCELERATED_MOVEMENTS : MOUSEKEY_WHEEL_DECELERATED_MOVEMENTS;
+    } else if (mousekey_repeat && mouse_timer) {
+        if (mk_wheel_interval != MOUSEKEY_WHEEL_BASE_MOVEMENTS) {
+            const float time_elapsed = timer_elapsed(mouse_timer) / 50;
+            speed = MOUSEKEY_WHEEL_INITIAL_MOVEMENTS +
+                1 * time_elapsed +
+                1 * 0.5 * time_elapsed * time_elapsed;
+        }
+        speed = speed > MOUSEKEY_WHEEL_BASE_MOVEMENTS ? MOUSEKEY_WHEEL_BASE_MOVEMENTS : speed;
+    }
+
+    mk_wheel_interval = 1000.0f / speed;
+
+    return 1;
+}
+
+#        else /* #ifndef MK_KINETIC_SPEED */
 
 static uint8_t move_unit(void) {
     uint16_t unit;
@@ -142,6 +208,7 @@ static uint8_t wheel_unit(void) {
     return (unit > MOUSEKEY_WHEEL_MAX ? MOUSEKEY_WHEEL_MAX : (unit == 0 ? 1 : unit));
 }
 
+#        endif /* #ifndef MK_KINETIC_SPEED */
 #    endif /* #ifndef MK_COMBINED */
 
 void mousekey_task(void) {
@@ -193,6 +260,12 @@ void mousekey_task(void) {
 }
 
 void mousekey_on(uint8_t code) {
+#ifdef MK_KINETIC_SPEED
+    if (mouse_timer == 0) {
+        mouse_timer = timer_read();
+    }
+#endif /* #ifdef MK_KINETIC_SPEED */
+
     if (code == KC_MS_UP)
         mouse_report.y = move_unit() * -1;
     else if (code == KC_MS_DOWN)
@@ -260,7 +333,12 @@ void mousekey_off(uint8_t code) {
         mousekey_accel &= ~(1 << 1);
     else if (code == KC_MS_ACCEL2)
         mousekey_accel &= ~(1 << 2);
-    if (mouse_report.x == 0 && mouse_report.y == 0) mousekey_repeat = 0;
+    if (mouse_report.x == 0 && mouse_report.y == 0) {
+        mousekey_repeat = 0;
+#ifdef MK_KINETIC_SPEED
+        mouse_timer = 0;
+#endif /* #ifdef MK_KINETIC_SPEED */
+    }
     if (mouse_report.v == 0 && mouse_report.h == 0) mousekey_wheel_repeat = 0;
 }
 
diff --git a/tmk_core/common/mousekey.h b/tmk_core/common/mousekey.h
index 05e4538234..703854b826 100644
--- a/tmk_core/common/mousekey.h
+++ b/tmk_core/common/mousekey.h
@@ -38,16 +38,28 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #    endif
 
 #    ifndef MOUSEKEY_MOVE_DELTA
+#ifndef MK_KINETIC_SPEED
 #        define MOUSEKEY_MOVE_DELTA 5
+#else
+#        define MOUSEKEY_MOVE_DELTA 25
+#endif
 #    endif
 #    ifndef MOUSEKEY_WHEEL_DELTA
 #        define MOUSEKEY_WHEEL_DELTA 1
 #    endif
 #    ifndef MOUSEKEY_DELAY
+#ifndef MK_KINETIC_SPEED
 #        define MOUSEKEY_DELAY 300
+#else
+#        define MOUSEKEY_DELAY 8
+#endif
 #    endif
 #    ifndef MOUSEKEY_INTERVAL
+#ifndef MK_KINETIC_SPEED
 #        define MOUSEKEY_INTERVAL 50
+#else
+#        define MOUSEKEY_INTERVAL 8
+#endif
 #    endif
 #    ifndef MOUSEKEY_MAX_SPEED
 #        define MOUSEKEY_MAX_SPEED 10
@@ -68,6 +80,31 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #        define MOUSEKEY_WHEEL_TIME_TO_MAX 40
 #    endif
 
+#ifndef MOUSEKEY_INITIAL_SPEED
+#define MOUSEKEY_INITIAL_SPEED  100
+#endif
+#ifndef MOUSEKEY_BASE_SPEED
+#define MOUSEKEY_BASE_SPEED 1000
+#endif
+#ifndef MOUSEKEY_DECELERATED_SPEED
+#define MOUSEKEY_DECELERATED_SPEED 400
+#endif
+#ifndef MOUSEKEY_ACCELERATED_SPEED
+#define MOUSEKEY_ACCELERATED_SPEED 3000
+#endif
+#ifndef MOUSEKEY_WHEEL_INITIAL_MOVEMENTS
+#define MOUSEKEY_WHEEL_INITIAL_MOVEMENTS  16
+#endif
+#ifndef MOUSEKEY_WHEEL_BASE_MOVEMENTS
+#define MOUSEKEY_WHEEL_BASE_MOVEMENTS  32
+#endif
+#ifndef MOUSEKEY_WHEEL_ACCELERATED_MOVEMENTS
+#define MOUSEKEY_WHEEL_ACCELERATED_MOVEMENTS  48
+#endif
+#ifndef MOUSEKEY_WHEEL_DECELERATED_MOVEMENTS
+#define MOUSEKEY_WHEEL_DECELERATED_MOVEMENTS  8
+#endif
+
 #else /* #ifndef MK_3_SPEED */
 
 #    ifndef MK_C_OFFSET_UNMOD