cursor: prevent hi-res mice triggering scroll actions too often

Hi-res mice produces mulitple scroll events with `delta_discrete` != 0
during a single "click". This patch makes them trigger `Scroll` actions
only when the accumulated `delta_discrete` exceeds 120 (= 1 click).

See https://lists.freedesktop.org/archives/wayland-devel/2019-April/040377.html
for how hi-res scroll events are reported.

diff --git a/include/labwc.h b/include/labwc.h
index cff785881e42224b549ea12a24fa31d5e2f60089..5f4ae1336deb57bd32c88b9a1c8c249478b04f79 100644 (file)
--- a/include/labwc.h
+++ b/include/labwc.h
@@ -111,9 +111,10 @@ struct seat {
        bool cursor_visible;
        struct wlr_cursor *cursor;
        struct wlr_xcursor_manager *xcursor_manager;
-       struct {
-               double x, y;
-       } smooth_scroll_offset;
+       struct accumulated_scroll {
+               double delta;
+               double delta_discrete;
+       } accumulated_scrolls[2]; /* indexed by wl_pointer_axis */
        bool cursor_scroll_wheel_emulation;
 
        /*

diff --git a/src/input/cursor.c b/src/input/cursor.c
index c5f9e4aed2763632446d591055dcaed859913158..d55e6bc0e6da46480dc4b0dec52d1f25dff58b53 100644 (file)
--- a/src/input/cursor.c
+++ b/src/input/cursor.c
@@ -1245,38 +1245,44 @@ struct scroll_info {
 };
 
 static struct scroll_info
-compare_delta(double delta, double delta_discrete, double *accum)
+compare_delta(double delta, double delta_discrete, struct accumulated_scroll *accum)
 {
-       /*
-        * Smooth scroll deltas are in surface space, so treating each unit as a
-        * scroll event would result in too-fast scrolling.
-        *
-        * This fudge factor (inherited from various historic projects, incl. Weston)
-        * produces events at a more reasonable rate.
-        *
-        * For historic context, see:
-        * https://lists.freedesktop.org/archives/wayland-devel/2019-April/040377.html
-        */
-       const double SCROLL_THRESHOLD = 10.0;
        struct scroll_info info = {0};
 
-       if (delta_discrete < 0 || delta < 0) {
-               info.direction = -1;
-       } else if (delta_discrete > 0 || delta > 0) {
-               info.direction = 1;
-       }
-
-       if (delta == 0.0) {
-               /* Delta 0 marks the end of a scroll */
-               *accum = 0.0;
+       if (delta_discrete) {
+               /* mice */
+               info.direction = delta_discrete > 0 ? 1 : -1;
+               accum->delta_discrete += delta_discrete;
+               /*
+                * Non-hi-res mice produce delta_discrete of ±120 for every
+                * "click", so it always triggers actions. But for hi-res mice
+                * that produce smaller delta_discrete, we accumulate it and
+                * run actions after it exceeds 120(= 1 click).
+                */
+               if (fabs(accum->delta_discrete) >= 120.0) {
+                       accum->delta_discrete = fmod(accum->delta_discrete, 120.0);
+                       info.run_action = true;
+               }
        } else {
-               /* Accumulate smooth scrolling until we hit threshold */
-               *accum += delta;
-       }
-
-       if (delta_discrete != 0 || fabs(*accum) > SCROLL_THRESHOLD) {
-               *accum = fmod(*accum, SCROLL_THRESHOLD);
-               info.run_action = true;
+               /* 2-finger scrolling on touchpads */
+               if (delta == 0) {
+                       /* delta=0 marks the end of a scroll */
+                       accum->delta = 0;
+                       return info;
+               }
+               info.direction = delta > 0 ? 1 : -1;
+               accum->delta += delta;
+               /*
+                * The threshold of 10 is inherited from various historic
+                * projects including weston.
+                *
+                * For historic context, see:
+                * https://lists.freedesktop.org/archives/wayland-devel/2019-April/040377.html
+                */
+               if (fabs(accum->delta) >= 10.0) {
+                       accum->delta = fmod(accum->delta, 10.0);
+                       info.run_action = true;
+               }
        }
 
        return info;
@@ -1290,21 +1296,16 @@ process_cursor_axis(struct server *server, enum wl_pointer_axis orientation,
        uint32_t modifiers = keyboard_get_all_modifiers(&server->seat);
 
        enum direction direction = LAB_DIRECTION_INVALID;
-       struct scroll_info info = {0};
+       struct scroll_info info = compare_delta(delta, delta_discrete,
+               &server->seat.accumulated_scrolls[orientation]);
 
        if (orientation == WL_POINTER_AXIS_HORIZONTAL_SCROLL) {
-               info = compare_delta(delta, delta_discrete,
-                       &server->seat.smooth_scroll_offset.x);
-
                if (info.direction < 0) {
                        direction = LAB_DIRECTION_LEFT;
                } else if (info.direction > 0) {
                        direction = LAB_DIRECTION_RIGHT;
                }
        } else if (orientation == WL_POINTER_AXIS_VERTICAL_SCROLL) {
-               info = compare_delta(delta, delta_discrete,
-                       &server->seat.smooth_scroll_offset.y);
-
                if (info.direction < 0) {
                        direction = LAB_DIRECTION_UP;
                } else if (info.direction > 0) {
@@ -1324,8 +1325,8 @@ process_cursor_axis(struct server *server, enum wl_pointer_axis orientation,
                                        && mousebind->mouse_event == MOUSE_ACTION_SCROLL) {
                                handled = true;
                                /*
-                                * Action may not be executed if the accumulated scroll
-                                * delta on touchpads doesn't exceed the threshold
+                                * Action may not be executed if the accumulated scroll delta
+                                * on touchpads or hi-res mice doesn't exceed the threshold
                                 */
                                if (info.run_action) {
                                        actions_run(ctx.view, server, &mousebind->actions, &ctx);