Re: [hackers] [slstatus][patch] Use ALSA for vol_perc on Linux

From: Ivan Tham <pickfire_AT_riseup.net>
Date: Sat, 23 May 2020 00:32:58 +0800

On Fri, May 22, 2020 at 11:58:23AM +0200, Thomas Vigouroux wrote:
>Quoting Ivan Tham (2020-05-22 10:52:21)
>> I believe you may need to convert it to double before division and round the
>> volume. My dwms have something similar:
>>
>> return smprintf("%d", (int) rint((double) (val - min) /
>> (double) (max - min) * 100));
>>
>> https://github.com/pickfire/dwms/blob/c2038a4104f4f80aa6f675821c62e87ccfe48bed/dwms.c#L213-L241
>
>Actually, multiplying before might avoid floating point computation and only uses integer computation.
>Thanks for your answer and suggestion !
>
>Here is an updated patch :
>
>diff --git a/components/volume.c b/components/volume.c
>index 61cec90..f2e5b70 100644
>--- a/components/volume.c
>+++ b/components/volume.c
>_AT_@ -72,6 +72,57 @@
>
> return bprintf("%d", m ? 0 : v * 100 / 255);
> }
>+#elif defined(__linux__)
>+ #include <alsa/asoundlib.h>
>+ #include <alsa/mixer.h>
>+
>+ const char *
>+ vol_perc(const char * card)
>+ {
>+ long minv, maxv, outvol;
>+ snd_mixer_t* handle;
>+ snd_mixer_elem_t* elem;
>+ snd_mixer_selem_id_t* sid;
>+
>+ static const char* mix_name = "Master";
>+ static int mix_index = 0;
>+
>+ snd_mixer_selem_id_alloca(&sid);
>+
>+ /* sets simple-mixer index and name */
>+ snd_mixer_selem_id_set_index(sid, mix_index);
>+ snd_mixer_selem_id_set_name(sid, mix_name);
>+
>+ if (snd_mixer_open(&handle, 0) < 0)
>+ return NULL;
>+ if (snd_mixer_attach(handle, card) < 0) {
>+ snd_mixer_close(handle);
>+ return NULL;
>+ }

There seemed to be a lot of repeated patterns, why not use goto like other C
projects to handle failure?

>+ if (snd_mixer_selem_register(handle, NULL, NULL) < 0) {
>+ snd_mixer_close(handle);
>+ return NULL;
>+ }
>+ if (snd_mixer_load(handle) < 0) {
>+ snd_mixer_close(handle);
>+ return NULL;
>+ }
>+ elem = snd_mixer_find_selem(handle, sid);
>+ if (!elem) {
>+ snd_mixer_close(handle);
>+ return NULL;
>+ }
>+
>+ snd_mixer_selem_get_playback_volume_range(elem, &minv, &maxv);
>+
>+ if(snd_mixer_selem_get_playback_volume(elem, 0, &outvol) < 0) {
>+ snd_mixer_close(handle);
>+ return NULL;
>+ }
>+
>+ snd_mixer_close(handle);
>+ return bprintf("%ld", (100 * (outvol - minv)) / (maxv - minv));

If I recall correctly, it is something like:

                const char* buf = NULL;

                ...

                if (failure)
                         goto error;
                ...

                buf = bprintf("%ld", (100 * (outvol - minv)) / (maxv - minv));

error:
                snd_mixer_close(handle);
                return buf;


Not sure if it is better like the other code I have seen but I think it reduces
the code duplication.

>+ }
> #else
> #include <sys/soundcard.h>
>
>diff --git a/config.def.h b/config.def.h
>index e06be66..af2197c 100644
>--- a/config.def.h
>+++ b/config.def.h
>_AT_@ -58,6 +58,7 @@ static const char unknown_str[] = "n/a";
> * uptime system uptime NULL
> * username username of current user NULL
> * vol_perc OSS/ALSA volume in percent mixer file (/dev/mixer)
>+ * sound card name on Linux (default)
> * wifi_perc WiFi signal in percent interface name (wlan0)
> * wifi_essid WiFi ESSID interface name (wlan0)
> */
>diff --git a/config.mk b/config.mk
>index 3b32b7c..cd2a234 100644
>--- a/config.mk
>+++ b/config.mk
>_AT_@ -14,7 +14,7 @@ X11LIB = /usr/X11R6/lib
> CPPFLAGS = -I$(X11INC) -D_DEFAULT_SOURCE
> CFLAGS = -std=c99 -pedantic -Wall -Wextra -Os
> LDFLAGS = -L$(X11LIB) -s
>-LDLIBS = -lX11
>+LDLIBS = -lX11 -lasound
>
> # compiler and linker
> CC = cc
Received on Fri May 22 2020 - 18:32:58 CEST

This archive was generated by hypermail 2.3.0 : Fri May 22 2020 - 18:36:35 CEST