From 80a9bdb999ced0b9bb740e4de870ed15a0c2337f Mon Sep 17 00:00:00 2001
From: Evan Goode <mail@evangoo.de>
Date: Sun, 19 Oct 2025 11:09:02 -0400
Subject: [PATCH] Smoothly handle VALUE120 scroll events

---
 glfw/wl_init.c | 14 ++++++++------
 kitty/mouse.c  | 19 +++++++++++++++----
 2 files changed, 23 insertions(+), 10 deletions(-)

diff --git a/glfw/wl_init.c b/glfw/wl_init.c
index d62aaafcf..eaa52d8de 100644
--- a/glfw/wl_init.c
+++ b/glfw/wl_init.c
@@ -202,21 +202,23 @@ pointer_handle_frame(void *data UNUSED, struct wl_pointer *pointer UNUSED) {
     _GLFWwindow* window = _glfw.wl.pointerFocus;
     if (!window) return;
     float x = 0, y = 0;
-    int highres = 0;
+    const int HIGHRES = 1;
+    const int VALUE120 = 1 << 4;
+    int flags = 0;
 
     if (info.discrete.y_axis_type != AXIS_EVENT_UNKNOWN) {
         y = info.discrete.y;
-        if (info.discrete.y_axis_type == AXIS_EVENT_VALUE120) y /= 120.f;
+        if (info.discrete.y_axis_type == AXIS_EVENT_VALUE120) flags |= VALUE120;
     } else if (info.continuous.y_axis_type != AXIS_EVENT_UNKNOWN) {
-        highres = 1;
+        flags |= HIGHRES;
         y = info.continuous.y;
     }
 
     if (info.discrete.x_axis_type != AXIS_EVENT_UNKNOWN) {
         x = info.discrete.x;
-        if (info.discrete.x_axis_type == AXIS_EVENT_VALUE120) x /= 120.f;
+        if (info.discrete.x_axis_type == AXIS_EVENT_VALUE120) flags |= VALUE120;
     } else if (info.continuous.x_axis_type != AXIS_EVENT_UNKNOWN) {
-        highres = 1;
+        flags |= HIGHRES;
         x = info.continuous.x;
     }
     /* clear pointer_curr_axis_info for next frame */
@@ -225,7 +227,7 @@ pointer_handle_frame(void *data UNUSED, struct wl_pointer *pointer UNUSED) {
     if (x != 0.0f || y != 0.0f) {
         float scale = (float)_glfwWaylandWindowScale(window);
         y *= scale; x *= scale;
-        _glfwInputScroll(window, -x, y, highres, _glfw.wl.xkb.states.modifiers);
+        _glfwInputScroll(window, -x, y, flags, _glfw.wl.xkb.states.modifiers);
     }
 }
 
diff --git a/kitty/mouse.c b/kitty/mouse.c
index 18193e6b4..92537857c 100644
--- a/kitty/mouse.c
+++ b/kitty/mouse.c
@@ -1162,7 +1162,7 @@ mouse_event(const int button, int modifiers, int action) {
 }
 
 static int
-scale_scroll(MouseTrackingMode mouse_tracking_mode, double offset, bool is_high_resolution, double *pending_scroll_pixels, int cell_size) {
+scale_scroll(MouseTrackingMode mouse_tracking_mode, double offset, bool is_high_resolution, bool is_value120, double *pending_scroll_pixels, int cell_size) {
 // scale the scroll by the multiplier unless the mouse is grabbed. If the mouse is grabbed only change direction.
 #define SCALE_SCROLL(which) { double scale = OPT(which); if (mouse_tracking_mode) scale /= fabs(scale); offset *= scale; }
     int s = 0;
@@ -1175,6 +1175,16 @@ scale_scroll(MouseTrackingMode mouse_tracking_mode, double offset, bool is_high_
         }
         s = (int)round(pixels) / cell_size;
         *pending_scroll_pixels = pixels - s * cell_size;
+    } else if (is_value120) {
+        SCALE_SCROLL(wheel_scroll_multiplier);
+        const double offset_lines = offset / 120.;
+        const double pixels = *pending_scroll_pixels + offset_lines * cell_size;
+        if (fabs(pixels) < cell_size) {
+            *pending_scroll_pixels = pixels;
+            return 0;
+        }
+        s = (int)round(pixels) / cell_size;
+        *pending_scroll_pixels = pixels - s * cell_size;
     } else {
         SCALE_SCROLL(wheel_scroll_multiplier);
         s = (int) round(offset);
@@ -1253,10 +1263,11 @@ scroll_event(double xoffset, double yoffset, int flags, int modifiers) {
             break;
     }
     int s;
-    bool is_high_resolution = flags & 1;
+    const bool is_high_resolution = flags & 1;
+    const bool is_value120 = flags & (1 << 4);
 
     if (yoffset != 0.0) {
-        s = scale_scroll(screen->modes.mouse_tracking_mode, yoffset, is_high_resolution, &screen->pending_scroll_pixels_y, global_state.callback_os_window->fonts_data->fcm.cell_height);
+        s = scale_scroll(screen->modes.mouse_tracking_mode, yoffset, is_high_resolution, is_value120, &screen->pending_scroll_pixels_y, global_state.callback_os_window->fonts_data->fcm.cell_height);
         if (s) {
             bool upwards = s > 0;
             if (screen->modes.mouse_tracking_mode) {
@@ -1277,7 +1288,7 @@ scroll_event(double xoffset, double yoffset, int flags, int modifiers) {
         }
     }
     if (xoffset != 0.0) {
-        s = scale_scroll(screen->modes.mouse_tracking_mode, xoffset, is_high_resolution, &screen->pending_scroll_pixels_x, global_state.callback_os_window->fonts_data->fcm.cell_width);
+        s = scale_scroll(screen->modes.mouse_tracking_mode, xoffset, is_high_resolution, is_value120, &screen->pending_scroll_pixels_x, global_state.callback_os_window->fonts_data->fcm.cell_width);
         if (s) {
             if (screen->modes.mouse_tracking_mode) {
                 int sz = encode_mouse_scroll(w, s > 0 ? 6 : 7, modifiers);