Wayland: Fix scroll offsets being inverted

Scrolling offsets were inverted compared to X11 and Win32.

Fixes #1463.

README.md

@@ -199,6 +199,8 @@ information on what to include when reporting a bug.
  - [Wayland] Bugfix: `CLOCK_MONOTONIC` was not correctly enabled
  - [Wayland] Bugfix: Repeated keys could be reported with `NULL` window (#1704)
  - [Wayland] Bugfix: Retrieving partial framebuffer size would segfault
+ - [Wayland] Bugfix: Scrolling offsets were inverted compared to other platforms
+   (#1463)
  - [POSIX] Bugfix: `CLOCK_MONOTONIC` was not correctly tested for or enabled
  - [NSGL] Removed enforcement of forward-compatible flag for core contexts
  - [NSGL] Bugfix: `GLFW_COCOA_RETINA_FRAMEBUFFER` had no effect on newer
@@ -345,6 +347,7 @@ skills.
  - ndogxj
  - Kristian Nielsen
  - Kamil Nowakowski
+ - onox
  - Denis Ovod
  - Ozzy
  - Andri Pálsson

src/wl_init.c

@@ -341,9 +341,9 @@ static void pointerHandleAxis(void* data,
            axis == WL_POINTER_AXIS_VERTICAL_SCROLL);
 
     if (axis == WL_POINTER_AXIS_HORIZONTAL_SCROLL)
-        x = wl_fixed_to_double(value) * scrollFactor;
+        x = -wl_fixed_to_double(value) * scrollFactor;
     else if (axis == WL_POINTER_AXIS_VERTICAL_SCROLL)
-        y = wl_fixed_to_double(value) * scrollFactor;
+        y = -wl_fixed_to_double(value) * scrollFactor;
 
     _glfwInputScroll(window, x, y);
 }