tearing: add fullscreen option

If set, labwc will try to automatically enable tearing for fullscreen
applications.

Fixes: #1557

docs/labwc-actions.5.scd

@@ -157,6 +157,7 @@ Actions are used in menus and keyboard/mouse bindings.
 
 *<action name="ToggleTearing" />*
 	Toggles tearing for the focused window.
+	Requires the config option 'allowTearing'.
 
 *<action name="FocusOutput" output="HDMI-A-1" />*
 	Give focus to topmost window on given output and warp the cursor

docs/labwc-config.5.scd

@@ -142,11 +142,14 @@ this is for compatibility with Openbox.
 	*fullscreen* enables adaptive sync whenever a window is in fullscreen
 	mode.
 
-*<core><allowTearing>* [yes|no]
+*<core><allowTearing>* [yes|no|fullscreen]
 	Allow tearing to reduce input lag. Default is no.
 	This option requires setting the environment variable
 	WLR_DRM_NO_ATOMIC=1.
-	*yes* allow tearing if requested by the active window.
+
+	*yes* allows tearing if requested by the active window.
+
+	*fullscreen* enables tearing automatically for fullscreen windows.
 
 *<core><reuseOutputMode>* [yes|no]
 	Try to re-use the existing output mode (resolution / refresh rate).

include/config/rcxml.h

@@ -35,6 +35,12 @@ enum adaptive_sync_mode {
 	LAB_ADAPTIVE_SYNC_FULLSCREEN,
 };
 
+enum tearing_mode {
+	LAB_TEARING_DISABLED = 0,
+	LAB_TEARING_ENABLED,
+	LAB_TEARING_FULLSCREEN,
+};
+
 enum tiling_events_mode {
 	LAB_TILING_EVENTS_NEVER = 0,
 	LAB_TILING_EVENTS_REGION = 1 << 0,
@@ -65,7 +71,7 @@ struct rcxml {
 	bool xdg_shell_server_side_deco;
 	int gap;
 	enum adaptive_sync_mode adaptive_sync;
-	bool allow_tearing;
+	enum tearing_mode allow_tearing;
 	bool reuse_output_mode;
 	enum view_placement_policy placement_policy;
 

src/config/rcxml.c

@@ -695,6 +695,18 @@ set_adaptive_sync_mode(const char *str, enum adaptive_sync_mode *variable)
 	}
 }
 
+static void
+set_tearing_mode(const char *str, enum tearing_mode *variable)
+{
+	if (!strcasecmp(str, "fullscreen")) {
+		*variable = LAB_TEARING_FULLSCREEN;
+	} else if (parse_bool(str, -1) == 1) {
+		*variable = LAB_TEARING_ENABLED;
+	} else {
+		*variable = LAB_TEARING_DISABLED;
+	}
+}
+
 static void
 entry(xmlNode *node, char *nodename, char *content)
 {
@@ -803,11 +815,11 @@ entry(xmlNode *node, char *nodename, char *content)
 	} else if (!strcasecmp(nodename, "adaptiveSync.core")) {
 		set_adaptive_sync_mode(content, &rc.adaptive_sync);
 	} else if (!strcasecmp(nodename, "allowTearing.core")) {
-		set_bool(content, &rc.allow_tearing);
+		set_tearing_mode(content, &rc.allow_tearing);
 		if (rc.allow_tearing) {
 			char *no_atomic_env = getenv("WLR_DRM_NO_ATOMIC");
 			if (!no_atomic_env || strcmp(no_atomic_env, "1") != 0) {
-				rc.allow_tearing = false;
+				rc.allow_tearing = LAB_TEARING_DISABLED;
 				wlr_log(WLR_ERROR, "tearing requires WLR_DRM_NO_ATOMIC=1");
 			}
 		}

src/output.c

@@ -44,6 +44,12 @@ get_tearing_preference(struct output *output)
 		return false;
 	}
 
+	/* If configured, automatically enable tearing for fullscreen applications */
+	if (rc.allow_tearing == LAB_TEARING_FULLSCREEN
+			&& server->active_view->fullscreen) {
+		return true;
+	}
+
 	/* If the active view requests tearing, or it is toggled on with action, allow it */
 	return server->active_view->tearing_hint;
 }