volume: Add LFE balance API

The gnome/unity-control-center UIs have a master volume slider, and
three sub-sliders: balance, fade, and subwoofer. Balance and fade
use PA's set_balance and set_fade APIs accordingly, but the subwoofer
slider sometimes does unintuitive things.

In order to make that slider behave better, let's add a LFE balance
API that these volume control UIs can use instead. With this API,
the UI can balance between "no subwoofer" and "only subwoofer" with
"equal balance" in the middle, which would make it more consistent
with the behaviour of the other sliders.

BugLink: https://bugzilla.gnome.org/show_bug.cgi?id=753847

Signed-off-by: David Henningsson <david.henningsson@canonical.com>

1 files changed, 13 insertions, 0 deletions

diff --git a/src/pulse/channelmap.c b/src/pulse/channelmap.c
index c342ef63a..c44dca411 100644
--- a/src/pulse/channelmap.c
+++ b/src/pulse/channelmap.c
@@ -684,6 +684,19 @@ int pa_channel_map_can_fade(const pa_channel_map *map) {
         (PA_CHANNEL_POSITION_MASK_REAR & m);
 }
 
+int pa_channel_map_can_lfe_balance(const pa_channel_map *map) {
+    pa_channel_position_mask_t m;
+
+    pa_assert(map);
+    pa_return_val_if_fail(pa_channel_map_valid(map), 0);
+
+    m = pa_channel_map_mask(map);
+
+    return
+        (PA_CHANNEL_POSITION_MASK_LFE & m) &&
+        (PA_CHANNEL_POSITION_MASK_HFE & m);
+}
+
 const char* pa_channel_map_to_name(const pa_channel_map *map) {
     pa_bitset_t in_map[PA_BITSET_ELEMENTS(PA_CHANNEL_POSITION_MAX)];
     unsigned c;