From bb56685063532f732f4fbdba1d890931dad3d891 Mon Sep 17 00:00:00 2001
From: Moritz Biering <moritzbiering.mb@gmail.com>
Date: Thu, 6 May 2021 14:32:57 +0200
Subject: [PATCH] Use the additional alpha-value as offset to support a
 changing alpha properly

---
 Xdefaults |  2 +-
 config.h  |  5 +++--
 x.c       | 17 +++++++++++++----
 3 files changed, 17 insertions(+), 7 deletions(-)

diff --git a/Xdefaults b/Xdefaults
index 2c2d2e0..040c772 100644
--- a/Xdefaults
+++ b/Xdefaults
@@ -1,6 +1,6 @@
 !! Transparency (0-1):
 st.alpha: 0.92
-st.alphaUnfocus: 0.62
+st.alphaOffset: 0.3
 
 !! Set a default font and font size as below:
 st.font: Monospace-11;
diff --git a/config.h b/config.h
index 3adf598..d6eeade 100644
--- a/config.h
+++ b/config.h
@@ -108,7 +108,8 @@ unsigned int tabspaces = 8;
 
 /* bg opacity */
 float alpha = 0.8;
-float alphaUnfocus = 0.8;
+float alphaOffset = 0.0;
+float alphaUnfocus;
 
 /* Terminal colors (16 first used in escape sequence) */
 static const char *colorname[] = {
@@ -219,7 +220,7 @@ ResourcePref resources[] = {
 		{ "cwscale",      FLOAT,   &cwscale },
 		{ "chscale",      FLOAT,   &chscale },
 		{ "alpha",        FLOAT,   &alpha },
-		{ "alphaUnfocus", FLOAT,   &alphaUnfocus },
+		{ "alphaOffset",  FLOAT,   &alphaOffset },
 };
 
 /*
diff --git a/x.c b/x.c
index d1721d7..2580d2a 100644
--- a/x.c
+++ b/x.c
@@ -182,6 +182,7 @@ static void xsetenv(void);
 static void xseturgency(int);
 static int evcol(XEvent *);
 static int evrow(XEvent *);
+static float clamp(float, float, float);
 
 static void expose(XEvent *);
 static void visibility(XEvent *);
@@ -319,10 +320,8 @@ changealpha(const Arg *arg)
 {
     if((alpha > 0 && arg->f < 0) || (alpha < 1 && arg->f > 0))
         alpha += arg->f;
-    if(alpha < 0)
-        alpha = 0;
-    if(alpha > 1)
-        alpha = 1;
+    alpha = clamp(alpha, 0.0, 1.0);
+    alphaUnfocus = clamp(alpha-alphaOffset, 0.0, 1.0);
 
     xloadcols();
     redraw();
@@ -381,6 +380,15 @@ evrow(XEvent *e)
 	return y / win.ch;
 }
 
+float
+clamp(float value, float lower, float upper) {
+    if(value < lower)
+        return lower;
+    if(value > upper)
+        return upper;
+    return value;
+}
+
 void
 mousesel(XEvent *e, int done)
 {
@@ -2298,6 +2306,7 @@ run:
 	cols = MAX(cols, 1);
 	rows = MAX(rows, 1);
 	defaultbg = MAX(LEN(colorname), 256);
+	alphaUnfocus = alpha-alphaOffset;
 	tnew(cols, rows);
 	xinit(cols, rows);
 	xsetenv();