c2: add new predefined target wm_state to match against `_NET_WM_ST…

…ATE` in string

New predefined target `wm_state` for rule-based matching. Matches
against the cached `_NET_WM_STATE` property of a window in string
representation.

NOTE: `wm_state = 'fullscreen'` is not neccessarily identical to
`fullscreen`, and `wm_state = 'focused'` is not identical to `focused`.

man/picom.1.asciidoc

@@ -274,7 +274,7 @@ With greater-than/less-than operators it looks like:
 
 'NEGATION' (optional) is one or more exclamation marks;
 
-'TARGET' is either a predefined target name, or the name of a window property to match. Supported predefined targets are `id`, `x`, `y`, `x2` (`x` + `widthb`), `y2` (like `x2`), `width`, `height`, `widthb` (`width` + 2 * `border_width`), `heightb` (like `widthb`), `border_width`, `fullscreen`, `override_redirect`, `argb` (whether the window has an ARGB visual), `focused`, `wmwin` (whether the window looks like a WM window, i.e. has no child window with `WM_STATE` and is not override-redirected), `bounding_shaped`, `rounded_corners` (requires *--detect-rounded-corners*), `client` (ID of client window), `window_type` (window type in string), `leader` (ID of window leader), `name`, `class_g` (= `WM_CLASS[1]`), `class_i` (= `WM_CLASS[0]`), and `role`.
+'TARGET' is either a predefined target name, or the name of a window property to match. Supported predefined targets are `id`, `x`, `y`, `x2` (`x` + `widthb`), `y2` (like `x2`), `width`, `height`, `widthb` (`width` + 2 * `border_width`), `heightb` (like `widthb`), `border_width`, `fullscreen`, `override_redirect`, `argb` (whether the window has an ARGB visual), `focused`, `wmwin` (whether the window looks like a WM window, i.e. has no child window with `WM_STATE` and is not override-redirected), `bounding_shaped`, `rounded_corners` (requires *--detect-rounded-corners*), `client` (ID of client window), `window_type` (window type in string), `leader` (ID of window leader), `name`, `class_g` (= `WM_CLASS[1]`), `class_i` (= `WM_CLASS[0]`), `role`, and `wm_state` (window manager state hint in string).
 
 'CLIENT/FRAME' is a single `@` if the window attribute should be be looked up on client window, nothing if on frame window;
 
@@ -307,6 +307,9 @@ Examples:
 	# If the window is a menu
 	window_type *= "menu"
 	_NET_WM_WINDOW_TYPE@:a *= "MENU"
+	# If the window is marked hidden
+	wm_state *= "hidden"
+	_NET_WM_STATE@:a *= "HIDDEN"
 	# If the window name contains "Firefox", ignore case
 	name *?= "Firefox"
 	_NET_WM_NAME@:s *?= "Firefox"

src/c2.c

@@ -133,6 +133,7 @@ struct _c2_l {
 	       C2_L_PCLASSG,
 	       C2_L_PCLASSI,
 	       C2_L_PROLE,
+	       C2_L_PWMSTATE,
 	} predef;
 	enum c2_l_type {
 		C2_L_TUNDEFINED,
@@ -210,6 +211,7 @@ static const c2_predef_t C2_PREDEFS[] = {
     [C2_L_PCLASSG] = {"class_g", C2_L_TSTRING, 0},
     [C2_L_PCLASSI] = {"class_i", C2_L_TSTRING, 0},
     [C2_L_PROLE] = {"role", C2_L_TSTRING, 0},
+    [C2_L_PWMSTATE] = {"wm_state", C2_L_TSTRING, 0},
 };
 
 /**
@@ -1395,10 +1397,21 @@ static inline void c2_match_once_leaf(session_t *ps, const struct managed_win *w
 			case C2_L_PCLASSG: tgt = w->class_general; break;
 			case C2_L_PCLASSI: tgt = w->class_instance; break;
 			case C2_L_PROLE: tgt = w->role; break;
+			case C2_L_PWMSTATE: {
+				ntargets = 0;
+				for (enum wm_state i = 1; i < NUM_WMSTATES; ++i) {
+					if (win_check_wm_state(w, i)) {
+						targets[ntargets++] = WMSTATES[i];
+					}
+				}
+				break;
+			}
 			default: assert(0); break;
 			}
-			ntargets = 1;
-			targets[0] = tgt;
+			if (tgt) {
+				ntargets = 1;
+				targets[0] = tgt;
+			}
 		}
 		// An atom type property, convert it to string
 		else if (pleaf->type == C2_L_TATOM) {

src/common.h

@@ -386,6 +386,7 @@ typedef struct session {
 typedef enum { WIN_EVMODE_UNKNOWN, WIN_EVMODE_FRAME, WIN_EVMODE_CLIENT } win_evmode_t;
 
 extern const char *const WINTYPES[NUM_WINTYPES];
+extern const char *const WMSTATES[NUM_WMSTATES];
 extern session_t *ps_g;
 
 void ev_xcb_error(session_t *ps, xcb_generic_error_t *err);

src/picom.c

@@ -84,6 +84,15 @@ const char *const WINTYPES[NUM_WINTYPES] = {
     "popup_menu", "tooltip", "notification", "combo",   "dnd",
 };
 
+/// Name string for window wm_states.
+const char *const WMSTATES[NUM_WMSTATES] = {
+    "unknown",           "modal",          "sticky",
+    "maximized_vert",    "maximized_horz", "shaded",
+    "skip_taskbar",      "skip_pager",     "hidden",
+    "fullscreen",        "above",          "below",
+    "demands_attention", "focused",
+};
+
 // clang-format off
 /// Names of backends.
 const char *const BACKEND_STRS[] = {[BKEND_XRENDER] = "xrender",

src/win.h

@@ -410,6 +410,9 @@ bool attr_pure win_is_fullscreen(const session_t *ps, const struct managed_win *
  */
 bool attr_pure win_is_focused_raw(const session_t *ps, const struct managed_win *w);
 
+/// check if window has specific wm_state.
+bool attr_pure win_check_wm_state(const struct managed_win *w, enum wm_state state);
+
 /// check if window has ARGB visual
 bool attr_pure win_has_alpha(const struct managed_win *w);