pulseaudio: Match channel map to SDL's chosen order

pa_channel_map_init_auto() with PA_CHANNEL_MAP_WAVEEX does the wrong
thing as it just takes the lest significant bits of
WAVEFORMATEXTENSIBLE's dwChannelMask in order. This doesn't match SDL's
chosen channel ordering.

The implementation here mirrors what we do for PipeWire.

Author: ivyl

src/audio/pulseaudio/SDL_pulseaudio.c

@@ -602,6 +602,71 @@ static void PulseStreamStateChangeCallback(pa_stream *stream, void *userdata)
     PULSEAUDIO_pa_threaded_mainloop_signal(pulseaudio_threaded_mainloop, 0);  // just signal any waiting code, it can look up the details.
 }
 
+// Channel maps that match the order in SDL_Audio.h
+static const pa_channel_position_t Pulse_map_1[] = { PA_CHANNEL_POSITION_MONO };
+static const pa_channel_position_t Pulse_map_2[] = { PA_CHANNEL_POSITION_FRONT_LEFT, PA_CHANNEL_POSITION_FRONT_RIGHT };
+
+static const pa_channel_position_t Pulse_map_3[] = { PA_CHANNEL_POSITION_FRONT_LEFT, PA_CHANNEL_POSITION_FRONT_RIGHT,
+                                                     PA_CHANNEL_POSITION_LFE };
+
+static const pa_channel_position_t Pulse_map_4[] = { PA_CHANNEL_POSITION_FRONT_LEFT, PA_CHANNEL_POSITION_FRONT_RIGHT,
+                                                     PA_CHANNEL_POSITION_REAR_LEFT, PA_CHANNEL_POSITION_REAR_RIGHT };
+
+static const pa_channel_position_t Pulse_map_5[] = { PA_CHANNEL_POSITION_FRONT_LEFT, PA_CHANNEL_POSITION_FRONT_RIGHT,
+                                                     PA_CHANNEL_POSITION_LFE,
+                                                     PA_CHANNEL_POSITION_REAR_LEFT, PA_CHANNEL_POSITION_REAR_RIGHT };
+
+static const pa_channel_position_t Pulse_map_6[] = { PA_CHANNEL_POSITION_FRONT_LEFT, PA_CHANNEL_POSITION_FRONT_RIGHT,
+                                                     PA_CHANNEL_POSITION_FRONT_CENTER, PA_CHANNEL_POSITION_LFE,
+                                                     PA_CHANNEL_POSITION_REAR_LEFT, PA_CHANNEL_POSITION_REAR_RIGHT };
+
+static const pa_channel_position_t Pulse_map_7[] = { PA_CHANNEL_POSITION_FRONT_LEFT, PA_CHANNEL_POSITION_FRONT_RIGHT,
+                                                     PA_CHANNEL_POSITION_FRONT_CENTER, PA_CHANNEL_POSITION_LFE,
+                                                     PA_CHANNEL_POSITION_REAR_CENTER,
+                                                     PA_CHANNEL_POSITION_SIDE_LEFT, PA_CHANNEL_POSITION_SIDE_RIGHT };
+
+static const pa_channel_position_t Pulse_map_8[] = { PA_CHANNEL_POSITION_FRONT_LEFT, PA_CHANNEL_POSITION_FRONT_RIGHT,
+                                                     PA_CHANNEL_POSITION_FRONT_CENTER, PA_CHANNEL_POSITION_LFE,
+                                                     PA_CHANNEL_POSITION_REAR_LEFT, PA_CHANNEL_POSITION_REAR_RIGHT,
+                                                     PA_CHANNEL_POSITION_SIDE_LEFT, PA_CHANNEL_POSITION_SIDE_RIGHT };
+
+#define COPY_CHANNEL_MAP(c) SDL_memcpy(pacmap->map, Pulse_map_##c, sizeof(Pulse_map_##c))
+
+static void PulseCreateChannelMap(pa_channel_map *pacmap, uint8_t channels)
+{
+    SDL_assert(channels <= PA_CHANNELS_MAX);
+
+    pacmap->channels = channels;
+
+    switch (channels) {
+    case 1:
+        COPY_CHANNEL_MAP(1);
+        break;
+    case 2:
+        COPY_CHANNEL_MAP(2);
+        break;
+    case 3:
+        COPY_CHANNEL_MAP(3);
+        break;
+    case 4:
+        COPY_CHANNEL_MAP(4);
+        break;
+    case 5:
+        COPY_CHANNEL_MAP(5);
+        break;
+    case 6:
+        COPY_CHANNEL_MAP(6);
+        break;
+    case 7:
+        COPY_CHANNEL_MAP(7);
+        break;
+    case 8:
+        COPY_CHANNEL_MAP(8);
+        break;
+    }
+
+}
+
 static bool PULSEAUDIO_OpenDevice(SDL_AudioDevice *device)
 {
     const bool recording = device->recording;
@@ -690,9 +755,8 @@ static bool PULSEAUDIO_OpenDevice(SDL_AudioDevice *device)
     PULSEAUDIO_pa_threaded_mainloop_lock(pulseaudio_threaded_mainloop);
 
     const char *name = SDL_GetHint(SDL_HINT_AUDIO_DEVICE_STREAM_NAME);
-    // The SDL ALSA output hints us that we use Windows' channel mapping
-    // https://bugzilla.libsdl.org/show_bug.cgi?id=110
-    PULSEAUDIO_pa_channel_map_init_auto(&pacmap, device->spec.channels, PA_CHANNEL_MAP_WAVEEX);
+
+    PulseCreateChannelMap(&pacmap, device->spec.channels);
 
     h->stream = PULSEAUDIO_pa_stream_new(
         pulseaudio_context,