fix: let Steam draw at the session's full size above 1080p

tools/linuxfs/overlay/usr/local/bin/droiddeck-steam-ui-scale

@@ -1,5 +1,10 @@
 #!/usr/bin/python3
-"""Initialize Steam's own Gamescope UI scale once; subsequent choices belong to Steam."""
+"""Initialize Steam's own Gamescope display settings once; subsequent choices belong to Steam.
+
+The UI scale, and native resolution: the client treats our gamescope as an external display and,
+unless "Enable Native Resolution on External Displays" is on, draws itself at 1920x1080 on any
+larger output - a 2340x1080 session came up as 16:9 with bars. The session's size is already the
+user's Resolution choice, so the client should use all of it."""
 import math
 import os
 from pathlib import Path
@@ -9,6 +14,7 @@ import tempfile
 
 
 DISPLAY = "External: gamescope|||Windowed"
+NATIVE_RESOLUTION = "EnableSteamNativeExternalResolution"
 TOKEN = re.compile(r'\s+|//[^\n]*|"(?:\\.|[^"\\])*"|[{}]')
 
 
@@ -102,6 +108,25 @@ def seed_text(text, scale):
     return text[:at] + insertion + text[at:], True
 
 
+def seed_native_resolution(text):
+    root = parse(text).get('InstallConfigStore')
+    if not isinstance(root, Block):
+        raise ValueError("missing InstallConfigStore")
+    gamescope = root.get('Gamescope')
+    if gamescope is not None and not isinstance(gamescope, Block):
+        raise ValueError("invalid Gamescope settings")
+    if gamescope is not None and gamescope.get(NATIVE_RESOLUTION) is not None:
+        return text, False
+    entry = f'"{NATIVE_RESOLUTION}" "1"'
+    if gamescope is not None:
+        at, indent = gamescope.end, 2
+    else:
+        entry = '"Gamescope"\n{\n' + entry + '\n}'
+        at, indent = root.end, 1
+    insertion = '\n' + '\n'.join('\t' * indent + line for line in entry.splitlines()) + '\n'
+    return text[:at] + insertion + text[at:], True
+
+
 def atomic_write(path, text):
     path.parent.mkdir(parents=True, exist_ok=True)
     fd, temporary = tempfile.mkstemp(prefix='.' + path.name, dir=path.parent)
@@ -128,9 +153,30 @@ def initialize(steam_root, width, height):
     return changed
 
 
+def initialize_native_resolution(steam_root):
+    config = Path(steam_root) / 'config/config.vdf'
+    marker = config.with_name('droiddeck-native-resolution-initialized')
+    if marker.exists():
+        return False
+    text = config.read_text() if config.exists() else '"InstallConfigStore"\n{\n}\n'
+    updated, changed = seed_native_resolution(text)
+    if changed:
+        atomic_write(config, updated)
+        print('== steam: native resolution on the session display')
+    atomic_write(marker, '1\n')
+    return changed
+
+
 if __name__ == '__main__':
+    status = 0
     try:
         initialize(sys.argv[1], int(sys.argv[2]), int(sys.argv[3]))
     except (OSError, ValueError, RecursionError) as error:
         print('== steam: left UI scale unchanged: ' + str(error), file=sys.stderr)
-        sys.exit(1)
+        status = 1
+    try:
+        initialize_native_resolution(sys.argv[1])
+    except (OSError, ValueError, RecursionError) as error:
+        print('== steam: left native resolution unchanged: ' + str(error), file=sys.stderr)
+        status = 1
+    sys.exit(status)

tools/tests/test_steam_ui_scale.py

@@ -11,6 +11,9 @@ seed_text = MODULE['seed_text']
 parse = MODULE['parse']
 initial_scale = MODULE['initial_scale']
 DISPLAY = MODULE['DISPLAY']
+seed_native_resolution = MODULE['seed_native_resolution']
+initialize_native_resolution = MODULE['initialize_native_resolution']
+NATIVE_RESOLUTION = MODULE['NATIVE_RESOLUTION']
 
 
 class SteamUiScaleTest(unittest.TestCase):
@@ -96,3 +99,55 @@ class SteamUiScaleTest(unittest.TestCase):
             initialize(self.root, 0, 720)
         self.assertFalse(self.config.exists())
         self.assertFalse(self.marker.exists())
+
+
+class SteamNativeResolutionTest(unittest.TestCase):
+    def setUp(self):
+        self.temp = tempfile.TemporaryDirectory()
+        self.addCleanup(self.temp.cleanup)
+        self.root = Path(self.temp.name)
+        self.config = self.root / 'config/config.vdf'
+        self.config.parent.mkdir()
+        self.marker = self.config.with_name('droiddeck-native-resolution-initialized')
+
+    def native(self, text):
+        return parse(text).get('InstallConfigStore').get('Gamescope').get(NATIVE_RESOLUTION)
+
+    def test_fresh_client_renders_at_the_session_size(self):
+        self.assertTrue(initialize_native_resolution(self.root))
+        self.assertEqual('1', self.native(self.config.read_text()))
+        self.assertTrue(self.marker.exists())
+
+    def test_existing_client_gets_it_once_beside_its_settings(self):
+        text = '"InstallConfigStore"\n{\n\t"Gamescope"\n\t{\n\t\t"HDREnabled"\t\t"1"\n\t}\n}\n'
+        self.config.write_text(text)
+        self.assertTrue(initialize_native_resolution(self.root))
+        updated = self.config.read_text()
+        self.assertEqual('1', self.native(updated))
+        self.assertEqual('1', parse(updated).get('InstallConfigStore').get('Gamescope').get('HDREnabled'))
+
+    def test_users_choice_is_kept(self):
+        text = f'"InstallConfigStore" {{ "Gamescope" {{ "{NATIVE_RESOLUTION}" "0" }} }}'
+        self.assertEqual((text, False), seed_native_resolution(text))
+
+    def test_turning_it_off_after_initialization_survives_restart(self):
+        initialize_native_resolution(self.root)
+        text = self.config.read_text().replace('"1"', '"0"')
+        self.config.write_text(text)
+        self.assertFalse(initialize_native_resolution(self.root))
+        self.assertEqual(text, self.config.read_text())
+
+    def test_ui_scale_and_native_resolution_seed_the_same_config(self):
+        initialize(self.root, 2340, 1080)
+        initialize_native_resolution(self.root)
+        text = self.config.read_text()
+        self.assertEqual('1', self.native(text))
+        self.assertIsNotNone(parse(text).get('InstallConfigStore').get('UI').get('display').get(DISPLAY))
+
+    def test_invalid_config_is_never_rewritten_or_marked_initialized(self):
+        for text in ('"InstallConfigStore" {', '"InstallConfigStore" { "Gamescope" "bad" }'):
+            self.config.write_text(text)
+            with self.assertRaises(ValueError):
+                initialize_native_resolution(self.root)
+            self.assertEqual(text, self.config.read_text())
+            self.assertFalse(self.marker.exists())