apply alpha patch (https://st.suckless.org/patches/alpha/)

config.def.h

@@ -93,11 +93,14 @@ char *termname = "st-256color";
  */
 unsigned int tabspaces = 8;
 
+/* bg opacity */
+float alpha = 0.95;
+
 /* Terminal colors (16 first used in escape sequence) */
 static const char *colorname[] = {
 
   /* 8 normal colors */
-  [0] = "#32302f", /* hard contrast: #1d2021 / soft contrast: #32302f */
+  [0] = "#1d2021", /* hard contrast: #1d2021 / soft contrast: #32302f */
   [1] = "#cc241d", /* red     */
   [2] = "#98971a", /* green   */
   [3] = "#d79921", /* yellow  */

config.mk

@@ -16,7 +16,7 @@ PKG_CONFIG = pkg-config
 INCS = -I$(X11INC) \
        `$(PKG_CONFIG) --cflags fontconfig` \
        `$(PKG_CONFIG) --cflags freetype2`
-LIBS = -L$(X11LIB) -lm -lrt -lX11 -lutil -lXft \
+LIBS = -L$(X11LIB) -lm -lrt -lX11 -lutil -lXft -lXrender\
        `$(PKG_CONFIG) --libs fontconfig` \
        `$(PKG_CONFIG) --libs freetype2`
 

patches/st-alpha-0.8.2.diff

@@ -0,0 +1,163 @@
+diff --git a/config.def.h b/config.def.h
+index 0e01717..e116631 100644
+--- a/config.def.h
++++ b/config.def.h
+@@ -82,6 +82,9 @@ char *termname = "st-256color";
+  */
+ unsigned int tabspaces = 8;
+ 
++/* bg opacity */
++float alpha = 0.8;
++
+ /* Terminal colors (16 first used in escape sequence) */
+ static const char *colorname[] = {
+ 	/* 8 normal colors */
+@@ -109,6 +112,7 @@ static const char *colorname[] = {
+ 	/* more colors can be added after 255 to use with DefaultXX */
+ 	"#cccccc",
+ 	"#555555",
++	"black",
+ };
+ 
+ 
+@@ -117,7 +121,7 @@ static const char *colorname[] = {
+  * foreground, background, cursor, reverse cursor
+  */
+ unsigned int defaultfg = 7;
+-unsigned int defaultbg = 0;
++unsigned int defaultbg = 258;
+ static unsigned int defaultcs = 256;
+ static unsigned int defaultrcs = 257;
+ 
+diff --git a/config.mk b/config.mk
+index 0cbb002..1d2f0e2 100644
+--- a/config.mk
++++ b/config.mk
+@@ -16,7 +16,7 @@ PKG_CONFIG = pkg-config
+ INCS = -I$(X11INC) \
+        `$(PKG_CONFIG) --cflags fontconfig` \
+        `$(PKG_CONFIG) --cflags freetype2`
+-LIBS = -L$(X11LIB) -lm -lrt -lX11 -lutil -lXft \
++LIBS = -L$(X11LIB) -lm -lrt -lX11 -lutil -lXft -lXrender\
+        `$(PKG_CONFIG) --libs fontconfig` \
+        `$(PKG_CONFIG) --libs freetype2`
+ 
+diff --git a/st.h b/st.h
+index 38c61c4..b7634ab 100644
+--- a/st.h
++++ b/st.h
+@@ -120,3 +120,4 @@ extern char *termname;
+ extern unsigned int tabspaces;
+ extern unsigned int defaultfg;
+ extern unsigned int defaultbg;
++extern float alpha;
+diff --git a/x.c b/x.c
+index 0422421..588dec3 100644
+--- a/x.c
++++ b/x.c
+@@ -98,6 +98,7 @@ typedef struct {
+ 	XSetWindowAttributes attrs;
+ 	int scr;
+ 	int isfixed; /* is fixed geometry? */
++	int depth; /* bit depth */
+ 	int l, t; /* left and top offset */
+ 	int gm; /* geometry mask */
+ } XWindow;
+@@ -229,6 +230,7 @@ static char *usedfont = NULL;
+ static double usedfontsize = 0;
+ static double defaultfontsize = 0;
+ 
++static char *opt_alpha = NULL;
+ static char *opt_class = NULL;
+ static char **opt_cmd  = NULL;
+ static char *opt_embed = NULL;
+@@ -688,7 +690,7 @@ xresize(int col, int row)
+ 
+ 	XFreePixmap(xw.dpy, xw.buf);
+ 	xw.buf = XCreatePixmap(xw.dpy, xw.win, win.w, win.h,
+-			DefaultDepth(xw.dpy, xw.scr));
++			xw.depth);
+ 	XftDrawChange(xw.draw, xw.buf);
+ 	xclear(0, 0, win.w, win.h);
+ 
+@@ -748,6 +750,13 @@ xloadcols(void)
+ 			else
+ 				die("could not allocate color %d\n", i);
+ 		}
++
++	/* set alpha value of bg color */
++	if (opt_alpha)
++		alpha = strtof(opt_alpha, NULL);
++	dc.col[defaultbg].color.alpha = (unsigned short)(0xffff * alpha);
++	dc.col[defaultbg].pixel &= 0x00FFFFFF;
++	dc.col[defaultbg].pixel |= (unsigned char)(0xff * alpha) << 24;
+ 	loaded = 1;
+ }
+ 
+@@ -1004,11 +1013,23 @@ xinit(int cols, int rows)
+ 	Window parent;
+ 	pid_t thispid = getpid();
+ 	XColor xmousefg, xmousebg;
++	XWindowAttributes attr;
++	XVisualInfo vis;
+ 
+ 	if (!(xw.dpy = XOpenDisplay(NULL)))
+ 		die("can't open display\n");
+ 	xw.scr = XDefaultScreen(xw.dpy);
+-	xw.vis = XDefaultVisual(xw.dpy, xw.scr);
++
++	if (!(opt_embed && (parent = strtol(opt_embed, NULL, 0)))) {
++		parent = XRootWindow(xw.dpy, xw.scr);
++		xw.depth = 32;
++	} else {
++		XGetWindowAttributes(xw.dpy, parent, &attr);
++		xw.depth = attr.depth;
++	}
++
++	XMatchVisualInfo(xw.dpy, xw.scr, xw.depth, TrueColor, &vis);
++	xw.vis = vis.visual;
+ 
+ 	/* font */
+ 	if (!FcInit())
+@@ -1018,7 +1039,7 @@ xinit(int cols, int rows)
+ 	xloadfonts(usedfont, 0);
+ 
+ 	/* colors */
+-	xw.cmap = XDefaultColormap(xw.dpy, xw.scr);
++	xw.cmap = XCreateColormap(xw.dpy, parent, xw.vis, None);
+ 	xloadcols();
+ 
+ 	/* adjust fixed window geometry */
+@@ -1038,19 +1059,15 @@ xinit(int cols, int rows)
+ 		| ButtonMotionMask | ButtonPressMask | ButtonReleaseMask;
+ 	xw.attrs.colormap = xw.cmap;
+ 
+-	if (!(opt_embed && (parent = strtol(opt_embed, NULL, 0))))
+-		parent = XRootWindow(xw.dpy, xw.scr);
+ 	xw.win = XCreateWindow(xw.dpy, parent, xw.l, xw.t,
+-			win.w, win.h, 0, XDefaultDepth(xw.dpy, xw.scr), InputOutput,
++			win.w, win.h, 0, xw.depth, InputOutput,
+ 			xw.vis, CWBackPixel | CWBorderPixel | CWBitGravity
+ 			| CWEventMask | CWColormap, &xw.attrs);
+ 
+ 	memset(&gcvalues, 0, sizeof(gcvalues));
+ 	gcvalues.graphics_exposures = False;
+-	dc.gc = XCreateGC(xw.dpy, parent, GCGraphicsExposures,
+-			&gcvalues);
+-	xw.buf = XCreatePixmap(xw.dpy, xw.win, win.w, win.h,
+-			DefaultDepth(xw.dpy, xw.scr));
++	xw.buf = XCreatePixmap(xw.dpy, xw.win, win.w, win.h, xw.depth);
++	dc.gc = XCreateGC(xw.dpy, xw.buf, GCGraphicsExposures, &gcvalues);
+ 	XSetForeground(xw.dpy, dc.gc, dc.col[defaultbg].pixel);
+ 	XFillRectangle(xw.dpy, xw.buf, dc.gc, 0, 0, win.w, win.h);
+ 
+@@ -1894,6 +1911,9 @@ main(int argc, char *argv[])
+ 	case 'a':
+ 		allowaltscreen = 0;
+ 		break;
++	case 'A':
++		opt_alpha = EARGF(usage());
++		break;
+ 	case 'c':
+ 		opt_class = EARGF(usage());
+ 		break;

st.h

@@ -123,3 +123,4 @@ extern char *termname;
 extern unsigned int tabspaces;
 extern unsigned int defaultfg;
 extern unsigned int defaultbg;
+extern float alpha;

x.c

@@ -105,6 +105,7 @@ typedef struct {
 	XSetWindowAttributes attrs;
 	int scr;
 	int isfixed; /* is fixed geometry? */
+	int depth; /* bit depth */
 	int l, t; /* left and top offset */
 	int gm; /* geometry mask */
 } XWindow;
@@ -243,6 +244,7 @@ static char *usedfont = NULL;
 static double usedfontsize = 0;
 static double defaultfontsize = 0;
 
+static char *opt_alpha = NULL;
 static char *opt_class = NULL;
 static char **opt_cmd  = NULL;
 static char *opt_embed = NULL;
@@ -734,7 +736,7 @@ xresize(int col, int row)
 
 	XFreePixmap(xw.dpy, xw.buf);
 	xw.buf = XCreatePixmap(xw.dpy, xw.win, win.w, win.h,
-			DefaultDepth(xw.dpy, xw.scr));
+			xw.depth);
 	XftDrawChange(xw.draw, xw.buf);
 	xclear(0, 0, win.w, win.h);
 
@@ -794,6 +796,12 @@ xloadcols(void)
 			else
 				die("could not allocate color %d\n", i);
 		}
+	/* set alpha value of bg color */
+	if (opt_alpha)
+		alpha = strtof(opt_alpha, NULL);
+	dc.col[defaultbg].color.alpha = (unsigned short)(0xffff * alpha);
+	dc.col[defaultbg].pixel &= 0x00FFFFFF;
+	dc.col[defaultbg].pixel |= (unsigned char)(0xff * alpha) << 24;
 	loaded = 1;
 }
 
@@ -1103,11 +1111,23 @@ xinit(int cols, int rows)
 	Window parent;
 	pid_t thispid = getpid();
 	XColor xmousefg, xmousebg;
+	XWindowAttributes attr;
+	XVisualInfo vis;
 
 	if (!(xw.dpy = XOpenDisplay(NULL)))
 		die("can't open display\n");
 	xw.scr = XDefaultScreen(xw.dpy);
-	xw.vis = XDefaultVisual(xw.dpy, xw.scr);
+
+	if (!(opt_embed && (parent = strtol(opt_embed, NULL, 0)))) {
+		parent = XRootWindow(xw.dpy, xw.scr);
+		xw.depth = 32;
+	} else {
+		XGetWindowAttributes(xw.dpy, parent, &attr);
+		xw.depth = attr.depth;
+	}
+
+	XMatchVisualInfo(xw.dpy, xw.scr, xw.depth, TrueColor, &vis);
+	xw.vis = vis.visual;
 
 	/* font */
 	if (!FcInit())
@@ -1117,7 +1137,7 @@ xinit(int cols, int rows)
 	xloadfonts(usedfont, 0);
 
 	/* colors */
-	xw.cmap = XDefaultColormap(xw.dpy, xw.scr);
+	xw.cmap = XCreateColormap(xw.dpy, parent, xw.vis, None);
 	xloadcols();
 
 	/* adjust fixed window geometry */
@@ -1137,19 +1157,15 @@ xinit(int cols, int rows)
 		| ButtonMotionMask | ButtonPressMask | ButtonReleaseMask;
 	xw.attrs.colormap = xw.cmap;
 
-	if (!(opt_embed && (parent = strtol(opt_embed, NULL, 0))))
-		parent = XRootWindow(xw.dpy, xw.scr);
 	xw.win = XCreateWindow(xw.dpy, parent, xw.l, xw.t,
-			win.w, win.h, 0, XDefaultDepth(xw.dpy, xw.scr), InputOutput,
+			win.w, win.h, 0, xw.depth, InputOutput,
 			xw.vis, CWBackPixel | CWBorderPixel | CWBitGravity
 			| CWEventMask | CWColormap, &xw.attrs);
 
 	memset(&gcvalues, 0, sizeof(gcvalues));
 	gcvalues.graphics_exposures = False;
-	dc.gc = XCreateGC(xw.dpy, parent, GCGraphicsExposures,
+	xw.buf = XCreatePixmap(xw.dpy, xw.win, win.w, win.h, xw.depth);
-			&gcvalues);
+	dc.gc = XCreateGC(xw.dpy, xw.buf, GCGraphicsExposures, &gcvalues);
-	xw.buf = XCreatePixmap(xw.dpy, xw.win, win.w, win.h,
-			DefaultDepth(xw.dpy, xw.scr));
 	XSetForeground(xw.dpy, dc.gc, dc.col[defaultbg].pixel);
 	XFillRectangle(xw.dpy, xw.buf, dc.gc, 0, 0, win.w, win.h);
 
@@ -1988,6 +2004,9 @@ main(int argc, char *argv[])
 	case 'a':
 		allowaltscreen = 0;
 		break;
+	case 'A':
+		opt_alpha = EARGF(usage());
+		break;
 	case 'c':
 		opt_class = EARGF(usage());
 		break;