Bug#883278: patch for xbacklight non-linear stepping

[Pieter-Tjerk de Boer <p.t.deboer@utwente.nl>]

I had the same wish, and implemented a -mul option for multiplying the
intensity by a number; as the number can be either >1 or <1, there's no
need for separate options for increasing and decreasing.
The patch is attached.

The patch also makes -set, -inc and -dec accept non-integer values without
truncating them.

Regards,
  Pieter-Tjerk

--- ./man/xbacklight.man.orig	2013-10-08 05:40:38.000000000 +0200
+++ ./man/xbacklight.man	2017-12-25 15:05:20.749299372 +0100
@@ -44,6 +44,10 @@
 Increases brightness by the specified amount.
 .IP "\-dec \fIpercent\fP"
 Decreases brightness by the specified amount.
+.IP "\-mul \fIfactor\fP"
+Multiplies brightness by the specified amount.
+If factor is not 1, the result is rounded such that the brightness does change,
+so this can be bound safely to a hotkey without getting stuck at 0.
 .IP \-help
 Print out a summary of the usage and exit.
 .IP "\-time \fImilliseconds\fP"
--- ./xbacklight.c.orig	2013-10-08 05:40:38.000000000 +0200
+++ ./xbacklight.c	2017-12-25 15:03:32.991542960 +0100
@@ -31,7 +31,7 @@
 #include <string.h>
 #include <unistd.h>
 
-typedef enum { Get, Set, Inc, Dec } op_t;
+typedef enum { Get, Set, Inc, Dec, Mul } op_t;
 
 static char *program_name;
 
@@ -47,6 +47,7 @@
             "  -set <percentage> or = <percentage>\n"
             "  -inc <percentage> or + <percentage>\n"
             "  -dec <percentage> or - <percentage>\n"
+            "  -mul <factor>     or * <factor> (note that the * may need a shell escape like \\* )\n"
             "  -get\n"
             "  -time <fade time in milliseconds>\n"
             "  -steps <number of steps in fade>\n");
@@ -107,7 +108,7 @@
 {
     char    *dpy_name = NULL;
     op_t    op = Get;
-    int	    value = 0;
+    double  value = 0;
     int	    i;
     int	    total_time = 200;	/* ms */
     int	    steps = 20;
@@ -137,39 +138,52 @@
 	{
 	    if (++i >= argc) usage();
 	    op = Set;
-	    value = atoi (argv[i]);
+	    value = atof (argv[i]);
 	    continue;
 	}
 	if (argv[i][0] == '=' && isdigit (argv[i][1]))
 	{
 	    op = Set;
-	    value = atoi (argv[i] + 1);
+	    value = atof (argv[i] + 1);
 	    continue;
 	}
 	if (!strcmp (argv[i], "-inc") || !strcmp (argv[i], "+"))
 	{
 	    if (++i >= argc) usage();
 	    op = Inc;
-	    value = atoi (argv[i]);
+	    value = atof (argv[i]);
 	    continue;
 	}
 	if (argv[i][0] == '+' && isdigit (argv[i][1]))
 	{
 	    op = Inc;
-	    value = atoi (argv[i] + 1);
+	    value = atof (argv[i] + 1);
 	    continue;
 	}
 	if (!strcmp (argv[i], "-dec") || !strcmp (argv[i], "-"))
 	{
 	    if (++i >= argc) usage();
 	    op = Dec;
-	    value = atoi (argv[i]);
+	    value = atof (argv[i]);
 	    continue;
 	}
 	if (argv[i][0] == '-' && isdigit (argv[i][1]))
 	{
 	    op = Dec;
-	    value = atoi (argv[i] + 1);
+	    value = atof (argv[i] + 1);
+	    continue;
+	}
+	if (!strcmp (argv[i], "-mul") || !strcmp (argv[i], "*"))
+	{
+	    if (++i >= argc) usage();
+	    op = Mul;
+	    value = atof (argv[i]);
+	    continue;
+	}
+	if (argv[i][0] == '*' && ( isdigit (argv[i][1]) || argv[i][1]=='.' ))
+	{
+	    op = Mul;
+	    value = atof (argv[i] + 1);
 	    continue;
 	}
 	if (!strcmp (argv[i], "-get") || !strcmp (argv[i], "-g"))
@@ -295,6 +309,14 @@
 			case Dec:
 			    new = cur - set;
 			    break;
+			case Mul:
+			    new = cur + (cur - min) * (value - 1);
+			    if ((long)(new+0.5) == (long)(cur+0.5)) {
+			       // ensure that there is some change after rounding
+                               if (value>1) new++;
+                               else if (value<1) new--;
+			    }
+			    break;
 			default:
 			    xcb_aux_sync (conn);
 			    return 1;
@@ -308,7 +330,7 @@
 				cur = new;
 			    else
 				cur += step;
-			    backlight_set (conn, output, (long) cur);
+			    backlight_set (conn, output, (long) (cur+0.5));  // +0.5 for proper rounding
 			    xcb_flush (conn);
 			    usleep (total_time * 1000 / steps);
 			}