Add Wayland support

Not everything is yet implemented, either for Godot or personal
limitations (I don't have all hardware in the world). A brief list of
the most important issues follows:

- Single-window only: the `DisplayServer` API doesn't expose enough
information for properly creating XDG shell windows.

- Very dumb rendering loop: this is very complicated, just know that
the low consumption mode is forced to 2000 Hz and some clever hacks are
in place to overcome a specific Wayland limitation. This will be
improved to the extent possible both downstream and upstream.

- Features to implement yet: IME, touch input, native file dialog,
drawing tablet (commented out due to a refactor), screen recording.

- Mouse passthrough can't be implement through a poly API, we need a
rect-based one.

- The cursor doesn't yet support fractional scaling.

- Auto scale is rounded up when using fractional scaling as we don't
have a per-window scale query API (basically we need
`DisplayServer::window_get_scale`).

- Building with `x11=no wayland=yes opengl=yes openxr=yes` fails.

This also adds a new project property and editor setting for selecting the
default DisplayServer to start, to allow this backend to start first in
exported projects (X11 is still the default for now). The editor setting
always overrides the project setting.

Special thanks to Drew Devault, toger5, Sebastian Krzyszkowiak, Leandro
Benedet Garcia, Subhransu, Yury Zhuravlev and Mara Huldra.

1 files changed, 41 insertions, 3 deletions

diff --git a/platform/linuxbsd/detect.py b/platform/linuxbsd/detect.py
index eaaaad82b9..e6a47f556d 100644
--- a/platform/linuxbsd/detect.py
+++ b/platform/linuxbsd/detect.py
@@ -47,6 +47,8 @@ def get_opts():
         BoolVariable("fontconfig", "Use fontconfig for system fonts support", True),
         BoolVariable("udev", "Use udev for gamepad connection callbacks", True),
         BoolVariable("x11", "Enable X11 display", True),
+        BoolVariable("wayland", "Enable Wayland display", True),
+        BoolVariable("libdecor", "Enable libdecor support", True),
         BoolVariable("touch", "Enable touch events", True),
         BoolVariable("execinfo", "Use libexecinfo on systems where glibc is not available", False),
     ]
@@ -204,6 +206,11 @@ def configure(env: "Environment"):
     if env["use_sowrap"]:
         env.Append(CPPDEFINES=["SOWRAP_ENABLED"])
 
+    if env["wayland"]:
+        if os.system("wayland-scanner -v") != 0:
+            print("wayland-scanner not found. Aborting.")
+            sys.exit(255)
+
     if env["touch"]:
         env.Append(CPPDEFINES=["TOUCH_ENABLED"])
 
@@ -364,9 +371,13 @@ def configure(env: "Environment"):
             env.ParseConfig("pkg-config xkbcommon --cflags --libs")
             env.Append(CPPDEFINES=["XKB_ENABLED"])
         else:
-            print(
-                "Warning: libxkbcommon development libraries not found. Disabling dead key composition and key label support."
-            )
+            if env["wayland"]:
+                print("Error: libxkbcommon development libraries required by Wayland not found. Aborting.")
+                sys.exit(255)
+            else:
+                print(
+                    "Warning: libxkbcommon development libraries not found. Disabling dead key composition and key label support."
+                )
     else:
         env.Append(CPPDEFINES=["XKB_ENABLED"])
 
@@ -433,6 +444,33 @@ def configure(env: "Environment"):
             env.ParseConfig("pkg-config xi --cflags --libs")
         env.Append(CPPDEFINES=["X11_ENABLED"])
 
+    if env["wayland"]:
+        if not env["use_sowrap"]:
+            if os.system("pkg-config --exists libdecor-0"):
+                print("Warning: libdecor development libraries not found. Disabling client-side decorations.")
+                env["libdecor"] = False
+            else:
+                env.ParseConfig("pkg-config libdecor-0 --cflags --libs")
+            if os.system("pkg-config --exists wayland-client"):
+                print("Error: Wayland client library not found. Aborting.")
+                sys.exit(255)
+            env.ParseConfig("pkg-config wayland-client --cflags --libs")
+            if os.system("pkg-config --exists wayland-cursor"):
+                print("Error: Wayland cursor library not found. Aborting.")
+                sys.exit(255)
+            env.ParseConfig("pkg-config wayland-cursor --cflags --libs")
+            if os.system("pkg-config --exists wayland-egl"):
+                print("Error: Wayland EGL library not found. Aborting.")
+                sys.exit(255)
+            env.ParseConfig("pkg-config wayland-egl --cflags --libs")
+
+        if env["libdecor"]:
+            env.Append(CPPDEFINES=["LIBDECOR_ENABLED"])
+
+        env.Prepend(CPPPATH=["#platform/linuxbsd", "#thirdparty/linuxbsd_headers/wayland/"])
+        env.Append(CPPDEFINES=["WAYLAND_ENABLED"])
+        env.Append(LIBS=["rt"])  # Needed by glibc, used by _allocate_shm_file
+
     if env["vulkan"]:
         env.Append(CPPDEFINES=["VULKAN_ENABLED", "RD_ENABLED"])
         if not env["use_volk"]: