fix: preserve accumulated drag-scroll distance, queued or coalesced

keyboards/bastardkb/charybdis/charybdis.c

@@ -186,25 +186,55 @@ static void pointing_device_task_charybdis(report_mouse_t* mouse_report) {
     static int16_t scroll_buffer_y = 0;
     if (g_charybdis_config.is_dragscroll_enabled) {
 #    ifdef CHARYBDIS_DRAGSCROLL_REVERSE_X
-        scroll_buffer_x -= mouse_report->x;
+        const int16_t m_x = -mouse_report->x;
 #    else
-        scroll_buffer_x += mouse_report->x;
+        const int16_t m_x = mouse_report->x;
 #    endif // CHARYBDIS_DRAGSCROLL_REVERSE_X
+        if (((m_x > 0) && (scroll_buffer_x < 0)) || ((m_x < 0) && (scroll_buffer_x > 0))) {
+            // Immediately cancel accunulated distance if mouse-direction reversed.
+            scroll_buffer_x = m_x;
+        } else {
+            scroll_buffer_x += m_x;
+        }
+        const int16_t abs_x = abs(scroll_buffer_x);
+        if (abs_x >= CHARYBDIS_DRAGSCROLL_BUFFER_SIZE) {
+            const int16_t sign_x = scroll_buffer_x > 0 ? 1 : -1;
+#    ifdef CHARYBDIS_DRAGSCROLL_SEND_COALESCED
+            mouse_report->h = sign_x * (abs_x / CHARYBDIS_DRAGSCROLL_BUFFER_SIZE);
+            scroll_buffer_x = sign_x * (abs_x % CHARYBDIS_DRAGSCROLL_BUFFER_SIZE);
+#    else
+            mouse_report->h = sign_x;
+            scroll_buffer_x -= sign_x * CHARYBDIS_DRAGSCROLL_BUFFER_SIZE;
+#    endif // CHARYBDIS_DRAGSCROLL_SEND_COALESCED
+        }
+
 #    ifdef CHARYBDIS_DRAGSCROLL_REVERSE_Y
-        scroll_buffer_y -= mouse_report->y;
+        const int16_t m_y = -mouse_report->y;
 #    else
-        scroll_buffer_y += mouse_report->y;
+        const int16_t m_y = mouse_report->y;
 #    endif // CHARYBDIS_DRAGSCROLL_REVERSE_Y
-        mouse_report->x = 0;
-        mouse_report->y = 0;
-        if (abs(scroll_buffer_x) > CHARYBDIS_DRAGSCROLL_BUFFER_SIZE) {
-            mouse_report->h = scroll_buffer_x > 0 ? 1 : -1;
-            scroll_buffer_x = 0;
+        if (((m_y > 0) && (scroll_buffer_y < 0)) || ((m_y < 0) && (scroll_buffer_y > 0))) {
+            // Immediately cancel accunulated distance if mouse-direction reversed.
+            scroll_buffer_y = m_y;
+        } else {
+            scroll_buffer_y += m_y;
         }
-        if (abs(scroll_buffer_y) > CHARYBDIS_DRAGSCROLL_BUFFER_SIZE) {
-            mouse_report->v = scroll_buffer_y > 0 ? 1 : -1;
-            scroll_buffer_y = 0;
+        const int16_t abs_y = abs(scroll_buffer_y);
+        if (abs_y >= CHARYBDIS_DRAGSCROLL_BUFFER_SIZE) {
+            const int16_t sign_y = scroll_buffer_y > 0 ? 1 : -1;
+#    ifdef CHARYBDIS_DRAGSCROLL_SEND_COALESCED
+            mouse_report->v = sign_y * (abs_y / CHARYBDIS_DRAGSCROLL_BUFFER_SIZE);
+            scroll_buffer_y = sign_y * (abs_y % CHARYBDIS_DRAGSCROLL_BUFFER_SIZE);
+#    else
+            mouse_report->v = sign_y;
+            scroll_buffer_y -= sign_y * CHARYBDIS_DRAGSCROLL_BUFFER_SIZE;
+#    endif // CHARYBDIS_DRAGSCROLL_SEND_COALESCED
         }
+
+        mouse_report->x = mouse_report->y = 0;
+    } else { // not a drag-scroll event
+        // Clean up, or next draa-scroll actevation would start abruptly.
+        scroll_buffer_x = scroll_buffer_y = 0;
     }
 }
 

keyboards/bastardkb/charybdis/readme.md

@@ -86,9 +86,16 @@ To invert the vertical scrolling direction (_ie._ mimic macOS "natural" scroll d
 ```c
 #define CHARYBDIS_DRAGSCROLL_REVERSE_Y
 ```
-
 This only affects the vertical scroll direction.
 
+
+By default, accumulated drag-scroll ±1 events from fast moves are queued and send through even after "wheel" has stopped moving.  To send scroll-wheel events with values greater than ±1,
+define `CHARYBDIS_DRAGSCROLL_SEND_COALESCED`:
+
+```c
+#define CHARYBDIS_DRAGSCROLL_SEND_COALESCED
+```
+
 ### Sniping mode
 
 Sniping mode slows down the pointer for more precise gestures. It is useful when combined with a higher default DPI.