add default transparency for windows and rules for override the transparency

config.def.h

@@ -4,15 +4,17 @@ static const unsigned int borderpx  = 1;  /* border pixel of windows */
 static const float rootcolor[]      = {0.3, 0.3, 0.3, 1.0};
 static const float bordercolor[]    = {0.5, 0.5, 0.5, 1.0};
 static const float focuscolor[]     = {1.0, 0.0, 0.0, 1.0};
+static const double default_alpha   = 0.75;
 
 /* tagging */
 static const char *tags[] = { "1", "2", "3", "4", "5", "6", "7", "8", "9" };
 
 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 },
-	{ "firefox",  NULL,       1 << 8,       0,           -1 },
+	{ "firefox",  NULL,       1 << 8,       0,           default_alpha   -1 },
+	{ "Alacritty",NULL,       1 << 2,       0,           1.0             -1 },
 	*/
 };
 
@@ -76,6 +78,8 @@ 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,          changealpha,    {.f = +0.1} },
+	{ MODKEY|WLR_MODIFIER_SHIFT, XKB_KEY_O,          changealpha,    {.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

@@ -111,6 +111,8 @@ typedef struct {
 	int bw;
 	unsigned int tags;
 	int isfloating, isurgent;
+	double alpha;
+	double prevalpha;
 	uint32_t resize; /* configure serial of a pending resize */
 	int prevx;
 	int prevy;
@@ -198,6 +200,7 @@ typedef struct {
 	const char *title;
 	unsigned int tags;
 	int isfloating;
+	double alpha;
 	int monitor;
 } Rule;
 
@@ -207,6 +210,7 @@ struct render_data {
 	struct wlr_output *output;
 	struct timespec *when;
 	int x, y; /* layout-relative */
+	double alpha;
 };
 
 /* function declarations */
@@ -221,6 +225,7 @@ static void arrangelayer(Monitor *m, struct wl_list *list,
 static void arrangelayers(Monitor *m);
 static void axisnotify(struct wl_listener *listener, void *data);
 static void buttonpress(struct wl_listener *listener, void *data);
+static void changealpha(const Arg *arg);
 static void chvt(const Arg *arg);
 static void cleanup(void);
 static void cleanupkeyboard(struct wl_listener *listener, void *data);
@@ -471,6 +476,7 @@ applyrules(Client *c)
 		if ((!r->title || strstr(title, r->title))
 				&& (!r->id || strstr(appid, r->id))) {
 			c->isfloating = r->isfloating;
+			c->alpha = r->alpha;
 			newtags |= r->tags;
 			i = 0;
 			wl_list_for_each(m, &mons, link)
@@ -678,6 +684,21 @@ buttonpress(struct wl_listener *listener, void *data)
 			event->time_msec, event->button, event->state);
 }
 
+void
+changealpha(const Arg *arg)
+{
+	Client *sel = selclient();
+
+	if (sel) {
+		sel->alpha += arg->f;
+		if (sel->alpha > 1.0)
+			sel->alpha = 1.0;
+
+		if (sel->alpha < 0.1)
+			sel->alpha = 0.1;
+	}
+}
+
 void
 chvt(const Arg *arg)
 {
@@ -893,6 +914,7 @@ createnotify(struct wl_listener *listener, void *data)
 	c = xdg_surface->data = calloc(1, sizeof(*c));
 	c->surface.xdg = xdg_surface;
 	c->bw = borderpx;
+	c->alpha = default_alpha;
 
 	LISTEN(&xdg_surface->surface->events.commit, &c->commit, commitnotify);
 	LISTEN(&xdg_surface->events.map, &c->map, mapnotify);
@@ -1033,10 +1055,13 @@ setfullscreen(Client *c, int fullscreen)
 		c->prevy = c->geom.y;
 		c->prevheight = c->geom.height;
 		c->prevwidth = c->geom.width;
+		c->prevalpha = c->alpha;
+		c->alpha = 1;
 		resize(c, c->mon->m.x, c->mon->m.y, c->mon->m.width, c->mon->m.height, 0);
 	} else {
 		/* restore previous size instead of arrange for floating windows since
 		 * client positions are set by the user and cannot be recalculated */
+		c->alpha = c->prevalpha;
 		resize(c, c->prevx, c->prevy, c->prevwidth, c->prevheight, 0);
 		arrange(c->mon);
 	}
@@ -1651,7 +1676,7 @@ render(struct wlr_surface *surface, int sx, int sy, void *data)
 
 	/* This takes our matrix, the texture, and an alpha, and performs the actual
 	 * rendering on the GPU. */
-	wlr_render_texture_with_matrix(drw, texture, matrix, 1);
+	wlr_render_texture_with_matrix(drw, texture, matrix, rdata->alpha);
 
 	/* This lets the client know that we've displayed that frame and it can
 	 * prepare another one now if it likes. */
@@ -1708,6 +1733,7 @@ renderclients(Monitor *m, struct timespec *now)
 		rdata.when = now;
 		rdata.x = c->geom.x + c->bw;
 		rdata.y = c->geom.y + c->bw;
+		rdata.alpha = c->alpha;
 		client_for_each_surface(c, render, &rdata);
 	}
 }
@@ -1722,6 +1748,7 @@ renderlayer(struct wl_list *layer_surfaces, struct timespec *now)
 			.when = now,
 			.x = layersurface->geo.x,
 			.y = layersurface->geo.y,
+			.alpha = 1,
 		};
 
 		wlr_surface_for_each_surface(layersurface->layer_surface->surface,
@@ -2480,6 +2507,7 @@ createnotifyx11(struct wl_listener *listener, void *data)
 	c->type = xwayland_surface->override_redirect ? X11Unmanaged : X11Managed;
 	c->bw = borderpx;
 	c->isfullscreen = 0;
+	c->alpha = default_alpha;
 
 	/* Listen to the various events it can emit */
 	LISTEN(&xwayland_surface->events.map, &c->map, mapnotify);
@@ -2528,6 +2556,8 @@ renderindependents(struct wlr_output *output, struct timespec *now)
 		rdata.when = now;
 		rdata.x = c->surface.xwayland->x;
 		rdata.y = c->surface.xwayland->y;
+		rdata.alpha = c->alpha;
+
 		wlr_surface_for_each_surface(c->surface.xwayland->surface, render, &rdata);
 	}
 }