meson: temporarily add check to conditionally enable the fade functionality

and in case it's missing, also #define some things to make compilation work,
since this is only available in a pipewire branch right now

meson.build

@@ -50,6 +50,19 @@ if ccpp.has_argument('-fvisibility=hidden')
   add_project_arguments('-fvisibility=hidden', language: 'cpp')
 endif
 
+have_audiofade = cc.compiles('''
+  #include <spa/utils/names.h>
+  #ifndef SPA_NAME_CONTROL_AUDIO_FADE_SOURCE
+  #error "not using the audio fade branch"
+  #endif
+  int main(void){return 0;}
+  ''',
+  name: 'audiofade',
+  dependencies: pipewire_dep)
+if have_audiofade
+  add_project_arguments('-DHAVE_AUDIOFADE', language: 'c')
+endif
+
 subdir('lib')
 subdir('docs')
 subdir('modules')

modules/module-config-policy/config-policy.c

@@ -7,7 +7,6 @@
  */
 
 #include <spa/utils/keys.h>
-#include <spa/param/control/audio.h>
 
 #include <pipewire/pipewire.h>
 
@@ -16,6 +15,12 @@
 #include "config-policy.h"
 #include "parser-endpoint-link.h"
 
+#if !defined(HAVE_AUDIOFADE)
+# define SPA_CONTROL_AUDIO_FADE_TYPE_LOGARITHMIC 2
+#else
+# include <spa/param/control/audio.h>
+#endif
+
 struct link_info {
   WpBaseEndpoint *ep;
   guint32 stream_id;

modules/module-pipewire/audio-softdsp-endpoint/convert.c

@@ -133,7 +133,12 @@ on_audio_convert_core_done (WpCore *core, GAsyncResult *res,
       &self->format);
 
   /* Only enable control port for input streams */
-  control = direction == PW_DIRECTION_INPUT;
+  control =
+#if defined(HAVE_AUDIOFADE)
+    (direction == PW_DIRECTION_INPUT);
+#else
+    FALSE;
+#endif
 
   /* Configure audioconvert to be both merger and splitter; this means it will
      have an equal number of input and output ports and just passthrough the

modules/module-pipewire/audio-softdsp-endpoint/stream.c

@@ -16,6 +16,14 @@
 
 #include "stream.h"
 
+#if !defined(HAVE_AUDIOFADE)
+# define SPA_PROP_audioFadeDuration 0x30001
+# define SPA_PROP_audioFadeStep 0x30002
+# define SPA_PROP_audioFadeDirection 0x30003
+# define SPA_PROP_audioFadeType 0x30004
+# define SPA_NAME_CONTROL_AUDIO_FADE_SOURCE "control.audio.fade.source"
+#endif
+
 typedef struct _WpAudioStreamPrivate WpAudioStreamPrivate;
 struct _WpAudioStreamPrivate
 {