From cd285922cdec966825e47220b1182a57abc1ff90 Mon Sep 17 00:00:00 2001
From: Scott Anderson <scott@anderso.nz>
Date: Mon, 6 Aug 2018 18:09:26 +1200
Subject: [PATCH] xwayland: use wayland axis_discrete event

This prevents multiple scroll events happening for wayland compositors
which send axis values other than 10. For example, libinput will
typically return 15 for each scroll wheel step, and if a wayland
compositor sends those to xwayland without normalising them, 2 scroll
wheel steps will end up as 3 xorg scroll events. By listening for the
discrete_axis event, this will now correctly send only 2 xorg scroll
events.

The wayland protocol gurantees that there will always be an axis event
following an axis_discrete event. However, it does not gurantee that
other events (including other axis_discrete+axis pairs) will not happen
in between them. So we must keep a list of outstanding axis_discrete
events.

Signed-off-by: Scott Anderson <scott@anderso.nz>
Reviewed-by: Peter Hutterer <peter.hutterer@who-t.net>
Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
---
 hw/xwayland/xwayland-input.c | 41 +++++++++++++++++++++++++++++++++++-
 hw/xwayland/xwayland.h       |  1 +
 2 files changed, 41 insertions(+), 1 deletion(-)

diff --git a/hw/xwayland/xwayland-input.c b/hw/xwayland/xwayland-input.c
index a602f0887..6fd3c416b 100644
--- a/hw/xwayland/xwayland-input.c
+++ b/hw/xwayland/xwayland-input.c
@@ -37,6 +37,12 @@
 #include <misc.h>
 #include "tablet-unstable-v2-client-protocol.h"
 
+struct axis_discrete_pending {
+    struct xorg_list l;
+    uint32_t axis;
+    int32_t discrete;
+};
+
 struct sync_pending {
     struct xorg_list l;
     DeviceIntPtr pending_dev;
@@ -565,6 +571,8 @@ pointer_handle_axis(void *data, struct wl_pointer *pointer,
     int index;
     const int divisor = 10;
     ValuatorMask mask;
+    struct axis_discrete_pending *pending = NULL;
+    struct axis_discrete_pending *iter;
 
     switch (axis) {
     case WL_POINTER_AXIS_VERTICAL_SCROLL:
@@ -577,8 +585,22 @@ pointer_handle_axis(void *data, struct wl_pointer *pointer,
         return;
     }
 
+    xorg_list_for_each_entry(iter, &xwl_seat->axis_discrete_pending, l) {
+        if (iter->axis == axis) {
+            pending = iter;
+            break;
+        }
+    }
+
     valuator_mask_zero(&mask);
-    valuator_mask_set_double(&mask, index, wl_fixed_to_double(value) / divisor);
+
+    if (pending) {
+        valuator_mask_set(&mask, index, pending->discrete);
+        xorg_list_del(&pending->l);
+        free(pending);
+    } else {
+        valuator_mask_set_double(&mask, index, wl_fixed_to_double(value) / divisor);
+    }
     QueuePointerEvents(xwl_seat->pointer, MotionNotify, 0, POINTER_RELATIVE, &mask);
 }
 
@@ -608,6 +630,16 @@ static void
 pointer_handle_axis_discrete(void *data, struct wl_pointer *wl_pointer,
                              uint32_t axis, int32_t discrete)
 {
+    struct xwl_seat *xwl_seat = data;
+
+    struct axis_discrete_pending *pending = malloc(sizeof *pending);
+    if (!pending)
+        return;
+
+    pending->axis = axis;
+    pending->discrete = discrete;
+
+    xorg_list_add(&pending->l, &xwl_seat->axis_discrete_pending);
 }
 
 static const struct wl_pointer_listener pointer_listener = {
@@ -1337,6 +1369,7 @@ create_input_device(struct xwl_screen *xwl_screen, uint32_t id, uint32_t version
     wl_array_init(&xwl_seat->keys);
 
     xorg_list_init(&xwl_seat->touches);
+    xorg_list_init(&xwl_seat->axis_discrete_pending);
     xorg_list_init(&xwl_seat->sync_pending);
 }
 
@@ -1345,6 +1378,7 @@ xwl_seat_destroy(struct xwl_seat *xwl_seat)
 {
     struct xwl_touch *xwl_touch, *next_xwl_touch;
     struct sync_pending *p, *npd;
+    struct axis_discrete_pending *ad, *ad_next;
 
     xorg_list_for_each_entry_safe(xwl_touch, next_xwl_touch,
                                   &xwl_seat->touches, link_touch) {
@@ -1357,6 +1391,11 @@ xwl_seat_destroy(struct xwl_seat *xwl_seat)
         free (p);
     }
 
+    xorg_list_for_each_entry_safe(ad, ad_next, &xwl_seat->axis_discrete_pending, l) {
+        xorg_list_del(&ad->l);
+        free(ad);
+    }
+
     release_tablet_manager_seat(xwl_seat);
 
     release_grab(xwl_seat);
diff --git a/hw/xwayland/xwayland.h b/hw/xwayland/xwayland.h
index d70ad54bf..1a6e2f380 100644
--- a/hw/xwayland/xwayland.h
+++ b/hw/xwayland/xwayland.h
@@ -272,6 +272,7 @@ struct xwl_seat {
     char *keymap;
     struct wl_surface *keyboard_focus;
 
+    struct xorg_list axis_discrete_pending;
     struct xorg_list sync_pending;
 
     struct xwl_pointer_warp_emulator *pointer_warp_emulator;