Draw the eyes one by one by default; multiview only with debug.multiview

On the Quest 3, in big online games (26-35 players), the picture was
doubled and shifted from the start as the head turned, nauseating; with
48 bots it was not, and with the eyes drawn one by one it was not online
either. Not the frame rate: one by one, online at 72 Hz, the compositor
repeated as many frames and nothing was seen. The Steam Frame had the
same doubling with multiview (2026-10-05) and draws them one by one
since. So both now do by default; debug.multiview (was vr.multiview, and
debug.multiview_steamvr) draws them at once, for finding what the shared
pass draws wrongly. The refresh rate's steps take up the extra cost.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

port/android/VR_ROADMAP.md

@@ -17,7 +17,7 @@ named where code is taken over.
 | Area | What |
 | --- | --- |
 | Headsets | Quest 3; Steam Frame (Lepton): its controllers' layout, a Steam library tile that installs, starts, updates and quits the game, data kept in `~/Documents/RingfallMjolnirVR` |
-| Rendering | Both eyes in one pass (multiview) on the Quest; one by one on SteamVR, where multiview's eyes did not fuse; lens flares at their depth in stereo; HUD, menus, scope, crosshair and names as layers of their own |
+| Rendering | The eyes drawn one by one (both at once, multiview, only with `debug.multiview`: its eyes did not always fuse, see the open points); lens flares at their depth in stereo; HUD, menus, scope, crosshair and names as layers of their own |
 | Aiming | The weapon in the hand, its shots from the muzzle, laser and crosshair options |
 | Body | Physical crouch (`vr.crouch_limit`) beside the crouch button, leaning (`vr.lean_limit`), melee by swinging, grenades thrown with the left hand, two-handed weapons |
 | Vehicles | The Warthog's wheel turned with the hands, right trigger throttle, left brake; first-person seats; turrets with handles |
@@ -518,6 +518,20 @@ see that nothing is missing or slower.
 
 ## Open points outside the order
 
+- Multiview's doubled pictures (2026-10-16): on the developer's Quest 3,
+  doubled and shifted pictures from the start of big online games (26-35
+  players) as the head turned, nauseating; none in a local game with 48
+  bots; none online either with the eyes drawn one by one. Not the frame
+  rate: one by one, online at 72 Hz, the compositor repeated as many
+  frames (about 4 a second) and nothing was seen. Not the facing jumps
+  (respawns only) nor the camera (it moves every frame). Before: the
+  Steam Frame's (2026-10-05), each eye alone sharp. So the eyes are drawn
+  one by one by default now (`debug.multiview` for both at once). To do:
+  find what the shared pass draws wrongly online, e.g. by saving both
+  eyes' pictures in a big online game and comparing what is doubled
+  (sprites and effects projected by the game itself, `mv_depth`; programs
+  made on the shader worker; the sky rows), then turn it back on: it
+  halves the drawing's CPU cost.
 - Big online games (2026-10-16): doubled pictures on a 32-player server,
   none in a local game with 48 bots. Not the GPU (60–80 %): the ticks cost
   3.3–4.6 ms as a client there (1.3–1.9 ms with bots or 16 players), so

port/linux/include/halo_vr.h

@@ -50,7 +50,7 @@ void halo_vr_eye_camera(int eye, const float game_position[3],
 /* copies the back buffer, just drawn for an eye, to that eye's image */
 void halo_vr_capture_eye(int eye);
 
-/* Both eyes in one draw (vr.multiview, where GL_OVR_multiview2 is): whether
+/* Both eyes in one draw (debug.multiview, where GL_OVR_multiview2 is): whether
 this frame draws so; the camera between the eyes whose view takes in both
 (as halo_vr_eye_camera), which also starts drawing into both eyes' layers;
 and after the draw, the layers taken for the eyes' images. */

port/linux/src/port_config.c

@@ -233,9 +233,6 @@ static const struct config_setting config_settings[] =
 		"away from the player's body (walls are not checked)." },
 	{ "vr.crouch_limit", _config_real, "0.9", "HALO_VR_CROUCH_LIMIT", _environment_value, _platform_android,
 		"How far, in metres, the view follows your head down." },
-	{ "vr.multiview", _config_boolean, "true", "HALO_VR_MULTIVIEW", _environment_value, _platform_android,
-		"Draw both eyes in one pass (GL_OVR_multiview2), from between them: about\n"
-		"half the drawing's cost on the processor. false: one eye after the other." },
 	{ "vr.log_performance", _config_boolean, "false", "HALO_VR_LOG_PERFORMANCE", _environment_value, _platform_android,
 		"Log the frame rate and where the frame time goes every five seconds\n"
 		"(adb logcat -s halo)." },
@@ -786,10 +783,12 @@ static const struct config_setting config_settings[] =
 		"machines of twice it), to test the netcode as over the internet; 0 none." },
 	{ "debug.network_loss", _config_real, "0.0", "HALO_NETWORK_LOSS", _environment_value, _platform_all,
 		"Percent of datagrams received that are dropped, for the same; 0 none." },
-	{ "debug.multiview_steamvr", _config_boolean, "false", "HALO_MULTIVIEW_STEAMVR", _environment_value,
-		_platform_android,
-		"On SteamVR (the Steam Frame) the eyes are drawn one by one, whatever\n"
-		"vr.multiview says: true draws them at once there too, for testing." },
+	{ "debug.multiview", _config_boolean, "false", "HALO_MULTIVIEW", _environment_value, _platform_android,
+		"Draw both eyes in one pass (GL_OVR_multiview2), from between them: about\n"
+		"half the drawing's cost on the processor, but the eyes' pictures did not\n"
+		"always fuse (doubled as the head turned: on the Steam Frame now and then,\n"
+		"on the Quest 3 in big online games). Off, one eye after the other; on,\n"
+		"for finding why." },
 	{ "debug.gl_thread", _config_integer, "-1", "HALO_GL_THREAD", _environment_value, _platform_android,
 		"Mesa's GL thread (its drivers: the Steam Frame's): 1 on, 0 off, -1 as the\n"
 		"driver chooses. Read when the app starts." },

port/linux/src/vr.c

@@ -138,7 +138,7 @@ static struct
 	float seat_frame_yaw;
 	int seat_frame_valid;
 	float seat_turn;
-	int multiview;              /* vr.multiview: both eyes in one draw */
+	int multiview;              /* debug.multiview: both eyes in one draw */
 	int multiview_logged;
 	int multiview_logged_views;
 	/* vr.foveation's level last logged (+1; 0: none yet) */
@@ -645,7 +645,7 @@ void halo_vr_initialize(void)
 	vr.two_hand_reach = (float)config_real("vr.two_hand_reach");
 	vr.melee_swing_speed = (float)config_real("vr.melee_swing_speed");
 	vr.grenade_throw_speed = (float)config_real("vr.grenade_throw_speed");
-	vr.multiview = config_boolean("vr.multiview");
+	vr.multiview = config_boolean("debug.multiview");
 	vr.vehicle_first_person = config_boolean("vr.vehicle_first_person");
 	vr.vehicle_spawn = config_boolean("debug.vehicle_spawn");
 	vr.turret_handles = config_boolean("vr.turret_handles");
@@ -678,16 +678,13 @@ void halo_vr_initialize(void)
 	vr.active = 1;
 	platform_log("VR: %s, eyes %dx%d at %.0f Hz", vr.info.system_name, vr.info.eye_width, vr.info.eye_height,
 		vr.info.refresh_rate);
-	/* SteamVR (the Steam Frame): each eye drawn apart. With both drawn at
-	once the eyes' pictures did not fuse, now and then: each alone was
-	sharp, the two together doubled as the head turned (2026-10-05), and
-	one by one costs it no more (its time goes to the driver either way).
-	debug.multiview_steamvr draws them at once there again, for finding why */
-	if (vr.multiview && strstr(vr.info.system_name, "SteamVR") && !config_boolean("debug.multiview_steamvr"))
-	{
-		vr.multiview = 0;
-		platform_log("VR: SteamVR: the eyes drawn one by one (debug.multiview_steamvr)");
-	}
+	/* Each eye drawn apart (debug.multiview draws both at once). At once,
+	the eyes' pictures did not always fuse: on the Steam Frame now and then
+	(each alone sharp, the two together doubled as the head turned,
+	2026-10-05; one by one costs it no more there), and on the Quest 3 in
+	big online games (doubled from the start as the head turned, none with
+	48 bots; one by one, none online either, 2026-10-16) */
+	platform_log("VR: the eyes drawn %s (debug.multiview)", vr.multiview ? "at once" : "one by one");
 }
 
 int halo_vr_active(void)
@@ -2161,7 +2158,7 @@ float halo_vr_refresh_rate(void)
 	return vr.active ? vr.info.refresh_rate : 0.0f;
 }
 
-/* ---------- both eyes at once (vr.multiview)
+/* ---------- both eyes at once (debug.multiview)
 
 The scene is drawn once, from a camera between the eyes whose view takes in
 both eyes' (with a margin, for what is near: the eyes stand apart), into two