add default transparency for windows and rules for override the transparency

config.def.h

@@ -12,6 +12,7 @@ static const float focuscolor[]            = COLOR(0x005577ff);
 static const float urgentcolor[]           = COLOR(0xff0000ff);
 /* To conform the xdg-protocol, set the alpha to zero to restore the old behavior */
 static const float fullscreen_bg[]         = {0.1, 0.1, 0.1, 1.0}; /* You can also use glsl colors */
+static const float default_opacity         = 0.75;
 
 /* tagging - TAGCOUNT must be no greater than 31 */
 #define TAGCOUNT (9)
@@ -20,11 +21,12 @@ static const float fullscreen_bg[]         = {0.1, 0.1, 0.1, 1.0}; /* You can al
 static int log_level = WLR_ERROR;
 
 static const Rule rules[] = {
-	/* app_id     title       tags mask     isfloating   monitor */
+	/* app_id     title       tags mask     isfloating   alpha           monitor */
 	/* examples:
-	{ "Gimp",     NULL,       0,            1,           -1 },
+	{ "Gimp",     NULL,       0,            1,           default_alpha,  -1 },
+	{ "Alacritty",NULL,       1 << 2,       0,           1.0,            -1 },
 	*/
-	{ "firefox",  NULL,       1 << 8,       0,           -1 },
+	{ "firefox",  NULL,       1 << 8,       0,           default_opacity, -1 },
 };
 
 /* layout(s) */
@@ -126,6 +128,8 @@ static const Key keys[] = {
 	{ MODKEY,                    XKB_KEY_d,          incnmaster,     {.i = -1} },
 	{ MODKEY,                    XKB_KEY_h,          setmfact,       {.f = -0.05} },
 	{ MODKEY,                    XKB_KEY_l,          setmfact,       {.f = +0.05} },
+	{ MODKEY,                    XKB_KEY_o,          setopacity,     {.f = +0.1} },
+	{ MODKEY|WLR_MODIFIER_SHIFT, XKB_KEY_O,          setopacity,     {.f = -0.1} },
 	{ MODKEY,                    XKB_KEY_Return,     zoom,           {0} },
 	{ MODKEY,                    XKB_KEY_Tab,        view,           {0} },
 	{ MODKEY|WLR_MODIFIER_SHIFT, XKB_KEY_C,          killclient,     {0} },

dwl.c

@@ -129,6 +129,7 @@ typedef struct {
 	unsigned int bw;
 	uint32_t tags;
 	int isfloating, isurgent, isfullscreen;
+	float opacity;
 	uint32_t resize; /* configure serial of a pending resize */
 } Client;
 
@@ -214,6 +215,7 @@ typedef struct {
 	const char *title;
 	uint32_t tags;
 	int isfloating;
+	float opacity;
 	int monitor;
 } Rule;
 
@@ -295,6 +297,7 @@ static void requeststartdrag(struct wl_listener *listener, void *data);
 static void requestmonstate(struct wl_listener *listener, void *data);
 static void resize(Client *c, struct wlr_box geo, int interact);
 static void run(char *startup_cmd);
+static void scenebuffersetopacity(struct wlr_scene_buffer *buffer, int sx, int sy, void *user_data);
 static void setcursor(struct wl_listener *listener, void *data);
 static void setcursorshape(struct wl_listener *listener, void *data);
 static void setfloating(Client *c, int floating);
@@ -303,6 +306,7 @@ static void setgamma(struct wl_listener *listener, void *data);
 static void setlayout(const Arg *arg);
 static void setmfact(const Arg *arg);
 static void setmon(Client *c, Monitor *m, uint32_t newtags);
+static void setopacity(const Arg *arg);
 static void setpsel(struct wl_listener *listener, void *data);
 static void setsel(struct wl_listener *listener, void *data);
 static void setup(void);
@@ -433,6 +437,7 @@ applyrules(Client *c)
 		if ((!r->title || strstr(title, r->title))
 				&& (!r->id || strstr(appid, r->id))) {
 			c->isfloating = r->isfloating;
+			c->opacity = r->opacity;
 			newtags |= r->tags;
 			i = 0;
 			wl_list_for_each(m, &mons, link)
@@ -440,6 +445,7 @@ applyrules(Client *c)
 					mon = m;
 		}
 	}
+	wlr_scene_node_for_each_buffer(&c->scene_surface->node, scenebuffersetopacity, c);
 	wlr_scene_node_reparent(&c->scene->node, layers[c->isfloating ? LyrFloat : LyrTile]);
 	setmon(c, mon, newtags);
 }
@@ -969,6 +975,7 @@ createnotify(struct wl_listener *listener, void *data)
 	c = xdg_surface->data = ecalloc(1, sizeof(*c));
 	c->surface.xdg = xdg_surface;
 	c->bw = borderpx;
+	c->opacity = default_opacity;
 
 	wlr_xdg_toplevel_set_wm_capabilities(xdg_surface->toplevel,
 			WLR_XDG_TOPLEVEL_WM_CAPABILITIES_FULLSCREEN);
@@ -2008,6 +2015,15 @@ run(char *startup_cmd)
 	wl_display_run(dpy);
 }
 
+void
+scenebuffersetopacity(struct wlr_scene_buffer *buffer, int sx, int sy, void *data)
+{
+	Client *c = data;
+	/* xdg-popups are children of Client.scene, we do not have to worry about
+	   messing with them. */
+	wlr_scene_buffer_set_opacity(buffer, c->isfullscreen ? 1 : c->opacity);
+}
+
 void
 setcursor(struct wl_listener *listener, void *data)
 {
@@ -2073,6 +2089,7 @@ setfullscreen(Client *c, int fullscreen)
 		 * client positions are set by the user and cannot be recalculated */
 		resize(c, c->prev, 0);
 	}
+	wlr_scene_node_for_each_buffer(&c->scene_surface->node, scenebuffersetopacity, c);
 	arrange(c->mon);
 	printstatus();
 }
@@ -2138,6 +2155,23 @@ setmon(Client *c, Monitor *m, uint32_t newtags)
 	focusclient(focustop(selmon), 1);
 }
 
+void
+setopacity(const Arg *arg)
+{
+	Client *sel = focustop(selmon);
+	if (!sel)
+		return;
+
+	sel->opacity += arg->f;
+	if (sel->opacity > 1.0)
+		sel->opacity = 1.0;
+
+	if (sel->opacity < 0.1)
+		sel->opacity = 0.1;
+
+	wlr_scene_node_for_each_buffer(&sel->scene_surface->node, scenebuffersetopacity, sel);
+}
+
 void
 setpsel(struct wl_listener *listener, void *data)
 {
@@ -2789,6 +2823,7 @@ createnotifyx11(struct wl_listener *listener, void *data)
 	c->surface.xwayland = xsurface;
 	c->type = xsurface->override_redirect ? X11Unmanaged : X11Managed;
 	c->bw = borderpx;
+	c->opacity = default_opacity;
 
 	/* Listen to the various events it can emit */
 	LISTEN(&xsurface->events.associate, &c->associate, associatex11);