Add "Custom Settings" string for gamescope

An easy way to add extra flags to gamescope.

lutris/runner_interpreter.py

@@ -118,6 +118,9 @@ def get_gamescope_args(launch_arguments, system_config):
         launch_arguments.insert(0, gamescope_fsr_sharpness)
         launch_arguments.insert(0, "--fsr-sharpness")
         launch_arguments.insert(0, "-U")
+    if system_config.get("gamescope_flags"):
+        gamescope_flags = system_config["gamescope_flags"]
+        launch_arguments.insert(0, gamescope_flags)
     if system_config.get("gamescope_window_mode"):
         gamescope_window_mode = system_config["gamescope_window_mode"]
         launch_arguments.insert(0, gamescope_window_mode)

lutris/sysoptions.py

@@ -356,6 +356,18 @@ system_options = [  # pylint: disable=invalid-name
                   "\n"
                   "<b>Empty string:</b> Disabled"),
     },
+    {
+        "section": "Gamescope",
+        "option": "gamescope_flags",
+        "label": _("Custom Settings"),
+        "advanced": True,
+        "type": "string",
+        "condition": bool(system.find_executable("gamescope")),
+        "help": _("Set additional flags for gamescope (if available).\n"
+                  "See 'gamescope --help' for a full list of options.\n"
+                  "\n"
+                  "<b>Empty String:</b> Disabled"),
+    },
     {
         "section": "CPU",
         "option": "single_cpu",