feat(volume): Add conversion functions

src/lua_libpulse_glib/volume.c

@@ -1,5 +1,7 @@
 #include "volume.h"
 
+#include "lua_util.h"
+
 #include <pulse/xmalloc.h>
 #include <stdbool.h>
 #include <stdio.h>
@@ -311,3 +313,31 @@ int volume_divide(lua_State* L) {
     }
     }
 }
+
+
+int volume_from_dB(lua_State* L) {
+    double value = (double) luaL_checknumber(L, 1);
+    lua_pushinteger(L, pa_sw_volume_from_dB(value));
+    return 1;
+}
+
+
+int volume_to_dB(lua_State* L) {
+    pa_volume_t value = luaL_checkinteger(L, 1);
+    lua_pushnumber(L, pa_sw_volume_to_dB(value));
+    return 1;
+}
+
+
+int volume_from_linear(lua_State* L) {
+    double value = (double) luaL_checknumber(L, 1);
+    lua_pushinteger(L, pa_sw_volume_from_linear(value));
+    return 1;
+}
+
+
+int volume_to_linear(lua_State* L) {
+    pa_volume_t value = luaL_checkinteger(L, 1);
+    lua_pushnumber(L, pa_sw_volume_to_linear(value));
+    return 1;
+}

src/lua_libpulse_glib/volume.h

@@ -55,7 +55,6 @@ int volume__newindex(lua_State*);
  */
 int volume_new(lua_State*);
 
-
 /** Checks whether a value is a valid @{Volume}.
  *
  * @function is_valid
@@ -64,6 +63,53 @@ int volume_new(lua_State*);
  */
 int volume_is_valid(lua_State*);
 
+/** Converts a decibel value to an integer volume value.
+ *
+ * This is only valid for software volumes. It does not operate
+ * on instances of @{Volume}.
+ *
+ * @function from_dB
+ * @tparam number value
+ * @treturn number
+ */
+int volume_from_dB(lua_State*);
+
+/** Converts an integer volume value to a decibel value.
+ *
+ * This is only valid for software volumes. It does not operate
+ * on instances of @{Volume}.
+ *
+ * @function to_dB
+ * @tparam number value
+ * @treturn number
+ */
+int volume_to_dB(lua_State*);
+
+/** Converts a linear factor to an integer volume value.
+ *
+ * `0.0` and less is muted, `1.0` is normal volume.
+ *
+ * This is only valid for software volumes. It does not operate
+ * on instances of @{Volume}.
+ *
+ * @function from_linear
+ * @tparam number value
+ * @treturn number
+ */
+int volume_from_linear(lua_State*);
+
+/** Converts an integer volume value to linear factor.
+ *
+ * This is only valid for software volumes. It does not operate
+ * on instances of @{Volume}.
+ *
+ * @function to_linear
+ * @tparam number value
+ * @treturn number
+ */
+int volume_to_linear(lua_State*);
+
+
 /// Volume
 /// @type Volume
 
@@ -237,7 +283,11 @@ static const struct luaL_Reg volume_mt[] = {
 
 static const struct luaL_Reg volume_lib[] = {
     {"new",          volume_new        },
-    { "is_valid", volume_is_valid},
+    { "from_dB",     volume_from_dB    },
+    { "to_dB",       volume_to_dB      },
+    { "from_linear", volume_from_linear},
+    { "to_linear",   volume_to_linear  },
+    { "is_valid",    volume_is_valid   },
     { NULL,          NULL              }
 };