Fix Wayland cursor offset when the cursor shape changes

The wayland protocol spec
https://wayland.freedesktop.org/docs/html/apa.html#protocol-spec-wl_pointer

States that `set_cursor` must be called with the serial number of the
`enter` event. However, GLFW is passing in the serial number of the latest
received event, which does not meet the protocol spec.

As a result, `set_cursor` calls were simply ignored by the compositor.

This fix complies with the protocol more closely by specifically caching the
`enter` event serial, and using it for all `set_cursor` calls.

Fixes #1706

README.md

@@ -229,6 +229,7 @@ information on what to include when reporting a bug.
  - [Wayland] Bugfix: Client-Side Decorations were destroyed in the wrong worder
    (#1798)
  - [Wayland] Bugfix: Monitors physical size could report zero (#1784,#1792)
+ - [Wayland] Bugfix: Non-arrow cursors are offset from the hotspot (#1706)
  - [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
@@ -455,7 +456,7 @@ skills.
  - Torsten Walluhn
  - Patrick Walton
  - Xo Wang
- - Waris
+ - Waris Boonyasiriwat
  - Jay Weisskopf
  - Frank Wille
  - Andy Williams
@@ -470,6 +471,8 @@ skills.
  - Jonas Ådahl
  - Lasse Öörni
  - Leonard König
+ - Koray Kilinc
+ - Joseph Chua
  - All the unmentioned and anonymous contributors in the GLFW community, for bug
    reports, patches, feedback, testing and encouragement
 

src/wl_init.c

@@ -105,6 +105,7 @@ static void pointerHandleEnter(void* data,
 
     window->wl.decorations.focus = focus;
     _glfw.wl.serial = serial;
+    _glfw.wl.pointerEnterSerial = serial;
     _glfw.wl.pointerFocus = window;
 
     window->wl.hovered = GLFW_TRUE;
@@ -164,7 +165,7 @@ static void setCursor(_GLFWwindow* window, const char* name)
     buffer = wl_cursor_image_get_buffer(image);
     if (!buffer)
         return;
-    wl_pointer_set_cursor(_glfw.wl.pointer, _glfw.wl.serial,
+    wl_pointer_set_cursor(_glfw.wl.pointer, _glfw.wl.pointerEnterSerial,
                           surface,
                           image->hotspot_x / scale,
                           image->hotspot_y / scale);

src/wl_platform.h

@@ -245,6 +245,7 @@ typedef struct _GLFWlibraryWayland
     const char*                 cursorPreviousName;
     int                         cursorTimerfd;
     uint32_t                    serial;
+    uint32_t                    pointerEnterSerial;
 
     int32_t                     keyboardRepeatRate;
     int32_t                     keyboardRepeatDelay;

src/wl_window.c

@@ -675,7 +675,7 @@ static void setCursorImage(_GLFWwindow* window,
         cursorWayland->yhot = image->hotspot_y;
     }
 
-    wl_pointer_set_cursor(_glfw.wl.pointer, _glfw.wl.serial,
+    wl_pointer_set_cursor(_glfw.wl.pointer, _glfw.wl.pointerEnterSerial,
                           surface,
                           cursorWayland->xhot / scale,
                           cursorWayland->yhot / scale);
@@ -1440,7 +1440,7 @@ static void lockPointer(_GLFWwindow* window)
     window->wl.pointerLock.relativePointer = relativePointer;
     window->wl.pointerLock.lockedPointer = lockedPointer;
 
-    wl_pointer_set_cursor(_glfw.wl.pointer, _glfw.wl.serial,
+    wl_pointer_set_cursor(_glfw.wl.pointer, _glfw.wl.pointerEnterSerial,
                           NULL, 0, 0);
 }
 
@@ -1504,7 +1504,7 @@ void _glfwPlatformSetCursor(_GLFWwindow* window, _GLFWcursor* cursor)
     }
     else if (window->cursorMode == GLFW_CURSOR_HIDDEN)
     {
-        wl_pointer_set_cursor(_glfw.wl.pointer, _glfw.wl.serial, NULL, 0, 0);
+        wl_pointer_set_cursor(_glfw.wl.pointer, _glfw.wl.pointerEnterSerial, NULL, 0, 0);
     }
 }