From 00dbe12e4196a781bb320070569274e2f1793a4d Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Daniel=20Ekl=C3=B6f?= <daniel@ekloef.se>
Date: Fri, 10 Apr 2020 18:43:29 +0200
Subject: [PATCH] input: slow trackpad scrolling now eventually scroll a line

Before, we converted each axis event's scroll amount to an integer and
scrolled that many lines.

However, axis events are speed sensitive - very slow scrolling will
result in events with a scroll amount that is < 1.0.

For us, this meant we never scrolled a single line. You could slow
scroll all day if you wanted, and still we would never scroll a single
line.

Fix this by aggregating the scroll amount from axis events until the
scroll amount is > 1.0, and then scroll.
---
 CHANGELOG.md |  1 +
 input.c      | 18 +++++++++++++++++-
 wayland.h    |  1 +
 3 files changed, 19 insertions(+), 1 deletion(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 372db0f6..0a336623 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -48,6 +48,7 @@
 * Hostname in OSC 7 URI not being validated.
 * OSC 4 with multiple `c;spec` pairs.
 * Alt+Return to emit "ESC \r".
+* Trackpad sloooow scrolling to eventually scroll a line.
 
 
 ### Security
diff --git a/input.c b/input.c
index 22cefa1e..8b18d168 100644
--- a/input.c
+++ b/input.c
@@ -1295,7 +1295,18 @@ wl_pointer_axis(void *data, struct wl_pointer *wl_pointer,
     if (wayl->mouse.have_discrete)
         return;
 
-    mouse_scroll(wayl, wl_fixed_to_int(value));
+    /*
+     * Aggregate scrolled amount until we get at least 1.0
+     *
+     * Without this, very slow scrolling will never actually scroll
+     * anything.
+     */
+    wayl->mouse.axis_aggregated += wl_fixed_to_double(value);
+
+    if (fabs(wayl->mouse.axis_aggregated) >= 1.) {
+        mouse_scroll(wayl, round(wayl->mouse.axis_aggregated));
+        wayl->mouse.axis_aggregated = 0.;
+    }
 }
 
 static void
@@ -1327,6 +1338,11 @@ static void
 wl_pointer_axis_stop(void *data, struct wl_pointer *wl_pointer,
                      uint32_t time, uint32_t axis)
 {
+    if (axis != WL_POINTER_AXIS_VERTICAL_SCROLL)
+        return;
+
+    struct wayland *wayl = data;
+    wayl->mouse.axis_aggregated = 0.;
 }
 
 const struct wl_pointer_listener pointer_listener = {
diff --git a/wayland.h b/wayland.h
index d827708c..e2abae72 100644
--- a/wayland.h
+++ b/wayland.h
@@ -292,6 +292,7 @@ struct wayland {
         struct timeval last_time;
 
         /* We used a discrete axis event in the current pointer frame */
+        double axis_aggregated;
         bool have_discrete;
     } mouse;