change alpha

config.h

@@ -93,6 +93,9 @@ char *termname = "xterm-256color";
  */
 unsigned int tabspaces = 8;
 
+/* Background opacity */
+float alpha_def;
+
 /* bg opacity */
 float alpha = 0.8;
 
@@ -226,7 +229,9 @@ static Shortcut shortcuts[] = {
 	{ TERMMOD,              XK_Num_Lock,    numlock,        {.i =  0} },
     { ShiftMask,            XK_Page_Up,     kscrollup,      {.i = -1} },
     { ShiftMask,            XK_Page_Down,   kscrolldown,    {.i = -1} },
-
+    { MODKEY,               XK_bracketleft, chgalpha,       {.f = -1} }, /* Decrease opacity */
+	{ MODKEY,               XK_bracketright,  chgalpha,       {.f = +1} }, /* Increase opacity */
+	{ MODKEY|ShiftMask,     XK_braceright,chgalpha,       {.f =  0} }, /* Reset opacity */
 };
 
 /*

st.h

@@ -127,3 +127,4 @@ extern unsigned int tabspaces;
 extern unsigned int defaultfg;
 extern unsigned int defaultbg;
 extern unsigned int defaultcs;
+extern float alpha_def;

x.c

@@ -60,6 +60,7 @@ static void zoom(const Arg *);
 static void zoomabs(const Arg *);
 static void zoomreset(const Arg *);
 static void ttysend(const Arg *);
+static void chgalpha(const Arg *);
 
 /* config.h for applying patches and the configuration. */
 #include "config.h"
@@ -1178,6 +1179,9 @@ xinit(int cols, int rows)
 
 	usedfont = (opt_font == NULL)? font : opt_font;
 	xloadfonts(usedfont, 0);
+    /* Backup default alpha value */
+    alpha_def = alpha;
+
 
 	/* colors */
 	xw.cmap = XCreateColormap(xw.dpy, parent, xw.vis, None);
@@ -1403,6 +1407,30 @@ xmakeglyphfontspecs(XftGlyphFontSpec *specs, const Glyph *glyphs, int len, int x
 	return numspecs;
 }
 
+void
+chgalpha(const Arg *arg)
+{
+   if (arg->f == -1.0f && alpha >= 0.1f)
+      alpha -= 0.1f;
+   else if (arg->f == 1.0f && alpha < 1.0f)
+      alpha += 0.1f;
+   else if (arg->f == 0.0f)
+      alpha = alpha_def;
+   else
+      return;
+
+    /* Clamp alpha so it never exceeds valid range */
+    if (alpha < 0.1f)
+        alpha = 0.1f;
+    if (alpha > 1.0f)
+        alpha = 1.0f;
+
+   dc.col[defaultbg].color.alpha = (unsigned short)(0xFFFF * alpha);
+   /* Required to remove artifacting from borderpx */
+   cresize(0, 0);
+   redraw();
+}
+
 void
 xdrawglyphfontspecs(const XftGlyphFontSpec *specs, Glyph base, int len, int x, int y)
 {