Wayland: Improve support for discrete scrolling

This adds support for high-resolution scroll input scaled to match
legacy discrete scroll input.  It is available on compositors that
support wl_seat version 8 or later.

High-resolution "discrete" values now replace non-scaled scroll
values when available.

README.md

@@ -152,6 +152,7 @@ information on what to include when reporting a bug.
  - [Wayland] Bugfix: The `libwayland-client` library was not unloaded at termination
  - [Wayland] Bugfix: Scroll events were sent twice on some versions of GNOME (#2494)
  - [Wayland] Bugfix: Two-dimensional scroll input was emitted as separate axes
+ - [Wayland] Bugfix: Mouse wheel scroll distance was incorrect on some compositors
  - [X11] Bugfix: Running without a WM could trigger an assert (#2593,#2601,#2631)
  - [X11] Bugfix: Occasional crash when an idle display awakes (#2766) 
  - [X11] Bugfix: Prevent BadWindow when creating small windows with a content scale

src/wl_init.c

@@ -135,7 +135,7 @@ static void registryHandleGlobal(void* userData,
         {
             _glfw.wl.seat =
                 wl_registry_bind(registry, name, &wl_seat_interface,
-                                 _glfw_min(5, version));
+                                 _glfw_min(8, version));
             _glfwAddSeatListenerWayland(_glfw.wl.seat);
         }
     }

src/wl_platform.h

@@ -478,6 +478,8 @@ typedef struct _GLFWlibraryWayland
         double                  pointerY;
         double                  scrollX;
         double                  scrollY;
+        double                  discreteX;
+        double                  discreteY;
         int                     button;
         int                     action;
     } pending;

src/wl_window.c

@@ -59,6 +59,7 @@
 #define GLFW_PENDING_BUTTON     2
 #define GLFW_PENDING_MOTION     4
 #define GLFW_PENDING_SCROLL     8
+#define GLFW_PENDING_DISCRETE   16
 
 static int createTmpfileCloexec(char* tmpname)
 {
@@ -1740,7 +1741,9 @@ static void pointerHandleFrame(void* userData, struct wl_pointer* pointer)
     if (_glfw.wl.pending.events & GLFW_PENDING_BUTTON)
         processPointerButton(_glfw.wl.pending.button, _glfw.wl.pending.action);
 
-    if (_glfw.wl.pending.events & GLFW_PENDING_SCROLL)
+    if (_glfw.wl.pending.events & GLFW_PENDING_DISCRETE)
+        processPointerScroll(_glfw.wl.pending.discreteX, _glfw.wl.pending.discreteY);
+    else if (_glfw.wl.pending.events & GLFW_PENDING_SCROLL)
         processPointerScroll(_glfw.wl.pending.scrollX, _glfw.wl.pending.scrollY);
 
     memset(&_glfw.wl.pending, 0, sizeof(_glfw.wl.pending));
@@ -1766,6 +1769,21 @@ static void pointerHandleAxisDiscrete(void* userData,
 {
 }
 
+static void pointerHandleAxisValue120(void* data,
+                                      struct wl_pointer* pointer,
+                                      uint32_t axis,
+                                      int32_t value120)
+{
+    if (!_glfw.wl.pointerSurface)
+        return;
+
+    _glfw.wl.pending.events |= GLFW_PENDING_DISCRETE;
+    if (axis == WL_POINTER_AXIS_HORIZONTAL_SCROLL)
+        _glfw.wl.pending.discreteX = -(value120 / 120.0);
+    else if (axis == WL_POINTER_AXIS_VERTICAL_SCROLL)
+        _glfw.wl.pending.discreteY = -(value120 / 120.0);
+}
+
 static const struct wl_pointer_listener pointerListener =
 {
     pointerHandleEnter,
@@ -1776,7 +1794,8 @@ static const struct wl_pointer_listener pointerListener =
     pointerHandleFrame,
     pointerHandleAxisSource,
     pointerHandleAxisStop,
-    pointerHandleAxisDiscrete
+    pointerHandleAxisDiscrete,
+    pointerHandleAxisValue120
 };
 
 static void keyboardHandleKeymap(void* userData,
@@ -1799,7 +1818,7 @@ static void keyboardHandleKeymap(void* userData,
         return;
     }
 
-    mapStr = mmap(NULL, size, PROT_READ, MAP_SHARED, fd, 0);
+    mapStr = mmap(NULL, size, PROT_READ, MAP_PRIVATE, fd, 0);
     if (mapStr == MAP_FAILED)
     {
         close(fd);