Partially handle _NET_WM_BYPASS_COMPOSITOR

Unredirect the screen when some window sets _NET_WM_BYPASS_COMPOSITOR
to 1, but ignore the case where some window requests the screen to be
redirected by setting _NET_WM_BYPASS_COMPOSITOR to 2.

Closes #267

Signed-off-by: Yuxuan Shui <yshuiv7@gmail.com>

src/atom.h

@@ -6,6 +6,7 @@
 #include "meta.h"
 #include "cache.h"
 
+// clang-format off
 // Splitted into 2 lists because of the limitation of our macros
 #define ATOM_LIST \
 	_NET_WM_WINDOW_OPACITY, \
@@ -36,7 +37,9 @@
 	_NET_WM_WINDOW_TYPE_COMBO, \
 	_NET_WM_WINDOW_TYPE_DND, \
 	_NET_WM_STATE, \
-	_NET_WM_STATE_FULLSCREEN
+	_NET_WM_STATE_FULLSCREEN, \
+	_NET_WM_BYPASS_COMPOSITOR
+// clang-format on
 
 #define ATOM_DEF(x) xcb_atom_t a##x
 

src/event.c

@@ -461,6 +461,11 @@ static inline void ev_property_notify(session_t *ps, xcb_property_notify_event_t
 			win_update_wintype(ps, w);
 	}
 
+	if (ev->atom == ps->atoms->a_NET_WM_BYPASS_COMPOSITOR) {
+		// Unnecessay until we remove the queue_redraw in ev_handle
+		queue_redraw(ps);
+	}
+
 	// If _NET_WM_OPACITY changes
 	if (ev->atom == ps->atoms->a_NET_WM_WINDOW_OPACITY) {
 		auto w = find_managed_win(ps, ev->window) ?: find_toplevel(ps, ev->window);

src/picom.c

@@ -81,12 +81,14 @@ const char *const WINTYPES[NUM_WINTYPES] = {
     "popup_menu", "tooltip", "notify", "combo",   "dnd",
 };
 
+// clang-format off
 /// Names of backends.
 const char *const BACKEND_STRS[] = {[BKEND_XRENDER] = "xrender",
                                     [BKEND_GLX] = "glx",
                                     [BKEND_XR_GLX_HYBRID] = "xr_glx_hybrid",
                                     [BKEND_DUMMY] = "dummy",
                                     NULL};
+// clang-format on
 
 // === Global variables ===
 
@@ -582,6 +584,17 @@ static struct managed_win *paint_preprocess(session_t *ps, bool *fade_running) {
 			}
 		}
 
+		// Unredirect screen if some window is requesting compositor bypass, even
+		// if that window is not on the top.
+		if (ps->o.unredir_if_possible && win_is_bypassing_compositor(ps, w) &&
+		    !w->unredir_if_possible_excluded) {
+			// Here we deviate from EWMH a bit. EWMH says we must not
+			// unredirect the screen if the window requesting bypassing would
+			// look different after unredirecting. Instead we always follow
+			// the request.
+			unredir_possible = true;
+		}
+
 		w->prev_trans = bottom;
 		if (bottom) {
 			w->stacking_rank = bottom->stacking_rank + 1;

src/win.c

@@ -2251,6 +2251,8 @@ static inline bool rect_is_fullscreen(const session_t *ps, int x, int y, int wid
 
 /**
  * Check if a window is fulscreen using EWMH
+ *
+ * TODO cache this property
  */
 static inline bool
 win_is_fullscreen_xcb(xcb_connection_t *c, const struct atom *a, const xcb_window_t w) {
@@ -2312,6 +2314,25 @@ bool win_is_fullscreen(const session_t *ps, const struct managed_win *w) {
 	       (!w->bounding_shaped || w->rounded_corners);
 }
 
+/**
+ * Check if a window has BYPASS_COMPOSITOR property set
+ *
+ * TODO cache this property
+ */
+bool win_is_bypassing_compositor(const session_t *ps, const struct managed_win *w) {
+	bool ret = false;
+
+	auto prop = x_get_prop(ps, w->client_win, ps->atoms->a_NET_WM_BYPASS_COMPOSITOR,
+	                       1L, XCB_ATOM_CARDINAL, 32);
+
+	if (prop.nitems && *prop.c32 == 1) {
+		ret = true;
+	}
+
+	free_winprop(&prop);
+	return ret;
+}
+
 /**
  * Check if a window is really focused.
  */

src/win.h

@@ -330,6 +330,10 @@ void win_update_leader(session_t *ps, struct managed_win *w);
  */
 // XXX was win_border_size
 void win_update_bounding_shape(session_t *ps, struct managed_win *w);
+/**
+ * Check if a window has BYPASS_COMPOSITOR property set
+ */
+bool win_is_bypassing_compositor(const session_t *ps, const struct managed_win *w);
 /**
  * Get a rectangular region in global coordinates a window (and possibly
  * its shadow) occupies.