Make Wayland momentum scrolling configurable

docs/changelog.rst

@@ -155,7 +155,7 @@ Detailed list of changes
 
 - Pixel scrolling for the kitty scrollback buffer controlled via :opt:`pixel_scroll` (:pull:`9330`)
 
-- Wayland: Add momentum scrolling in the kitty scrollback buffer for touchpads and touchscreens
+- Wayland: momentum scrolling in the kitty scrollback buffer for touchpads and touchscreens, see :opt:`momentum_scroll`
 
 - choose-files kitten: Fix JXL image preview not working (:iss:`9323`)
 

glfw/glfw.py

@@ -327,6 +327,7 @@ def generate_wrappers(glfw_header: str) -> None:
     bool glfwWaylandIsWindowFullyCreated(GLFWwindow *handle)
     bool glfwWaylandBeep(GLFWwindow *handle)
     pid_t glfwWaylandCompositorPID(void)
+    void glfwConfigureMomentumScroller(double friction, double min_velocity, double max_velocity, unsigned timer_interval)
     unsigned long long glfwDBusUserNotify(const GLFWDBUSNotificationData *n, GLFWDBusnotificationcreatedfun callback, void *data)
     void glfwDBusSetUserNotificationHandler(GLFWDBusnotificationactivatedfun handler)
     int glfwSetX11LaunchCommand(GLFWwindow *handle, char **argv, int argc)

glfw/momentum-scroll.c

@@ -42,16 +42,15 @@ static const MomentumScroller defaults = {
     .friction = 0.04,
     .min_velocity = 0.5,
     .max_velocity = 100,
-    .velocity_scale = 0.9,
     .timer_interval = 10,
 };
 static MomentumScroller s = defaults;
 
 GLFWAPI void
-glfwConfigureMomentumScroller(double friction, double min_velocity, double max_velocity, double velocity_scale, unsigned timer_interval_ms) {
-    s.timer_interval = ms_to_monotonic_t(timer_interval_ms);
+glfwConfigureMomentumScroller(double friction, double min_velocity, double max_velocity, unsigned timer_interval_ms) {
+    s.timer_interval = timer_interval_ms ? ms_to_monotonic_t(timer_interval_ms) : defaults.timer_interval;
 #define S(w) s.w = w >= 0 ? w : defaults.w
-    S(friction); S(min_velocity); S(max_velocity); S(velocity_scale);
+    S(friction); S(min_velocity); S(max_velocity);
 #undef S
 }
 
@@ -94,7 +93,6 @@ trim_old_samples(monotonic_t now) {
 
 static void
 add_velocity(double x, double y) {
-    x *= s.velocity_scale; y *= s.velocity_scale;
     if (x == 0 || x * s.velocity.x >= 0) s.velocity.x += x;
     else s.velocity.x = x;
     if (y == 0 || y * s.velocity.y >= 0) s.velocity.y += y;
@@ -185,7 +183,7 @@ glfw_handle_scroll_event_for_momentum(
     _GLFWwindow *w, const GLFWScrollEvent *ev, bool stopped, bool is_finger_based
 ) {
     if (!w) { cancel_existing_scroll(true); return; }
-    if (!is_finger_based || ev->offset_type != GLFW_SCROLL_OFFEST_HIGHRES || s.friction <= 0) {
+    if (!is_finger_based || ev->offset_type != GLFW_SCROLL_OFFEST_HIGHRES || s.friction < 0 || s.friction >= 1) {
         _glfwInputScroll(w, ev);
         return;
     }
@@ -210,7 +208,7 @@ glfw_handle_scroll_event_for_momentum(
     if (ldx * ev->x_offset < 0 || ldy * ev->y_offset < 0) cancel_existing_scroll(true);
     s.window_id = w->id;
     s.keyboard_modifiers = ev->keyboard_modifiers;
-    if (ev->offset_type == GLFW_SCROLL_OFFEST_HIGHRES && s.friction > 0) {
+    if (ev->offset_type == GLFW_SCROLL_OFFEST_HIGHRES) {
         add_sample(ev->unscaled.x, ev->unscaled.y, now);
         if (stopped) s.state = is_suitable_for_momentum() ? MOMENTUM_IN_PROGRESS : NONE;
         else s.state = PHYSICAL_EVENT_IN_PROGRESS;

kitty/glfw-wrapper.c

@@ -512,6 +512,9 @@ load_glfw(const char* path) {
     *(void **) (&glfwWaylandCompositorPID_impl) = dlsym(handle, "glfwWaylandCompositorPID");
     if (glfwWaylandCompositorPID_impl == NULL) dlerror(); // clear error indicator
 
+    *(void **) (&glfwConfigureMomentumScroller_impl) = dlsym(handle, "glfwConfigureMomentumScroller");
+    if (glfwConfigureMomentumScroller_impl == NULL) dlerror(); // clear error indicator
+
     *(void **) (&glfwDBusUserNotify_impl) = dlsym(handle, "glfwDBusUserNotify");
     if (glfwDBusUserNotify_impl == NULL) dlerror(); // clear error indicator
 

kitty/glfw-wrapper.h

@@ -2406,6 +2406,10 @@ typedef pid_t (*glfwWaylandCompositorPID_func)(void);
 GFW_EXTERN glfwWaylandCompositorPID_func glfwWaylandCompositorPID_impl;
 #define glfwWaylandCompositorPID glfwWaylandCompositorPID_impl
 
+typedef void (*glfwConfigureMomentumScroller_func)(double, double, double, unsigned);
+GFW_EXTERN glfwConfigureMomentumScroller_func glfwConfigureMomentumScroller_impl;
+#define glfwConfigureMomentumScroller glfwConfigureMomentumScroller_impl
+
 typedef unsigned long long (*glfwDBusUserNotify_func)(const GLFWDBUSNotificationData*, GLFWDBusnotificationcreatedfun, void*);
 GFW_EXTERN glfwDBusUserNotify_func glfwDBusUserNotify_impl;
 #define glfwDBusUserNotify glfwDBusUserNotify_impl

kitty/glfw.c

@@ -1354,6 +1354,7 @@ create_os_window(PyObject UNUSED *self, PyObject *args, PyObject *kw) {
 
     static bool is_first_window = true;
     if (is_first_window) {
+        if (global_state.is_wayland) glfwConfigureMomentumScroller(OPT(momentum_scroll), -1, -1, 0);
         glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, OPENGL_REQUIRED_VERSION_MAJOR);
         glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, OPENGL_REQUIRED_VERSION_MINOR);
         glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, true);

kitty/options/definition.py

@@ -597,6 +597,14 @@ running inside the terminal (for example full-screen TUIs) that handle scrolling
 themselves.
 ''')
 
+opt('momentum_scroll', '0.04', option_type='unit_float', ctype='float', long_text='''
+The amount of friction to apply to slow down momentum (inertial) scrolling. A number
+from 0 to 1, with 1 meaning no momentum scrolling. Note that this setting only
+applies on platforms such as Wayland, that do not provide native momentum scrolling.
+On macOS, the native OS based momentum scrolling is used. Also, momentum scrolling
+only applies to "finger" based devices such as touchpads and touchscreens. Changes
+to this setting only take effect after a kitty restart.
+''')
 egr()  # }}}
 
 

kitty/options/parse.py

@@ -1143,6 +1143,9 @@ class Parser:
         for k, v in modify_font(val):
             ans["modify_font"][k] = v
 
+    def momentum_scroll(self, val: str, ans: dict[str, typing.Any]) -> None:
+        ans['momentum_scroll'] = unit_float(val)
+
     def mouse_hide_wait(self, val: str, ans: dict[str, typing.Any]) -> None:
         ans['mouse_hide_wait'] = mouse_hide_wait(val)
 

kitty/options/to-c-generated.h

@@ -512,6 +512,19 @@ convert_from_opts_pixel_scroll(PyObject *py_opts, Options *opts) {
     Py_DECREF(ret);
 }
 
+static void
+convert_from_python_momentum_scroll(PyObject *val, Options *opts) {
+    opts->momentum_scroll = PyFloat_AsFloat(val);
+}
+
+static void
+convert_from_opts_momentum_scroll(PyObject *py_opts, Options *opts) {
+    PyObject *ret = PyObject_GetAttrString(py_opts, "momentum_scroll");
+    if (ret == NULL) return;
+    convert_from_python_momentum_scroll(ret, opts);
+    Py_DECREF(ret);
+}
+
 static void
 convert_from_python_mouse_hide_wait(PyObject *val, Options *opts) {
     mouse_hide_wait(val, opts);
@@ -1437,6 +1450,8 @@ convert_opts_from_python_opts(PyObject *py_opts, Options *opts) {
     if (PyErr_Occurred()) return false;
     convert_from_opts_pixel_scroll(py_opts, opts);
     if (PyErr_Occurred()) return false;
+    convert_from_opts_momentum_scroll(py_opts, opts);
+    if (PyErr_Occurred()) return false;
     convert_from_opts_mouse_hide_wait(py_opts, opts);
     if (PyErr_Occurred()) return false;
     convert_from_opts_url_color(py_opts, opts);

kitty/options/types.py

@@ -397,6 +397,7 @@ option_names = (
     'mark3_foreground',
     'menu_map',
     'modify_font',
+    'momentum_scroll',
     'mouse_hide_wait',
     'mouse_map',
     'narrow_symbols',
@@ -589,6 +590,7 @@ class Options:
     mark2_foreground: Color = Color(0, 0, 0)
     mark3_background: Color = Color(242, 116, 188)
     mark3_foreground: Color = Color(0, 0, 0)
+    momentum_scroll: float = 0.04
     mouse_hide_wait: MouseHideWait = MouseHideWait(hide_wait=0.0, show_wait=0.0, show_threshold=40, scroll_show=True) if is_macos else MouseHideWait(hide_wait=3.0, show_wait=0.0, show_threshold=40, scroll_show=True)
     notify_on_cmd_finish: NotifyOnCmdFinish = NotifyOnCmdFinish(when='never', duration=5.0, action='notify', cmdline=(), clear_on=('focus', 'next'))
     open_url_with: list[str] = ['default']

kitty/state.h

@@ -139,6 +139,7 @@ typedef struct Options {
     unsigned undercurl_style;
     struct { float thickness; int unit; } underline_exclusion;
     float box_drawing_scale[4];
+    double momentum_scroll;
 } Options;
 
 typedef struct WindowLogoRenderData {