Allow calling BackendBase::open multiple times on playback devices

It will not be called while the device is running. If the first call succeeds,
a subsequent call that happens to fail must leave the existing device state as
it was so it can be resumed.

This is a rough first pass. It will fail when trying to re-open the same device
which can only be opened once (for instance, with direct hardware access, on
hardware that doesn't do its own mixing). Some backends won't guarantee the new
device is usable until the reset() or start() call.

1 files changed, 23 insertions, 18 deletions

diff --git a/alc/backends/sdl2.cpp b/alc/backends/sdl2.cpp
index 084b51c0..4c4c71ed 100644
--- a/alc/backends/sdl2.cpp
+++ b/alc/backends/sdl2.cpp
@@ -106,32 +106,34 @@ void Sdl2Backend::open(const char *name)
     /* Passing nullptr to SDL_OpenAudioDevice opens a default, which isn't
      * necessarily the first in the list.
      */
+    SDL_AudioDeviceID devid;
     if(!name || strcmp(name, defaultDeviceName) == 0)
-        mDeviceID = SDL_OpenAudioDevice(nullptr, SDL_FALSE, &want, &have,
-            SDL_AUDIO_ALLOW_ANY_CHANGE);
+        devid = SDL_OpenAudioDevice(nullptr, SDL_FALSE, &want, &have, SDL_AUDIO_ALLOW_ANY_CHANGE);
     else
     {
         const size_t prefix_len = strlen(DEVNAME_PREFIX);
         if(strncmp(name, DEVNAME_PREFIX, prefix_len) == 0)
-            mDeviceID = SDL_OpenAudioDevice(name+prefix_len, SDL_FALSE, &want, &have,
+            devid = SDL_OpenAudioDevice(name+prefix_len, SDL_FALSE, &want, &have,
                 SDL_AUDIO_ALLOW_ANY_CHANGE);
         else
-            mDeviceID = SDL_OpenAudioDevice(name, SDL_FALSE, &want, &have,
-                SDL_AUDIO_ALLOW_ANY_CHANGE);
+            devid = SDL_OpenAudioDevice(name, SDL_FALSE, &want, &have, SDL_AUDIO_ALLOW_ANY_CHANGE);
     }
-    if(mDeviceID == 0)
+    if(!devid)
         throw al::backend_exception{al::backend_error::NoDevice, "%s", SDL_GetError()};
 
-    mDevice->Frequency = static_cast<uint>(have.freq);
-
+    DevFmtChannels devchans{};
     if(have.channels == 1)
-        mDevice->FmtChans = DevFmtMono;
+        devchans = DevFmtMono;
     else if(have.channels == 2)
-        mDevice->FmtChans = DevFmtStereo;
+        devchans = DevFmtStereo;
     else
+    {
+        SDL_CloseAudioDevice(devid);
         throw al::backend_exception{al::backend_error::DeviceError,
             "Unhandled SDL channel count: %d", int{have.channels}};
+    }
 
+    DevFmtType devtype{};
     switch(have.format)
     {
     case AUDIO_U8:     mDevice->FmtType = DevFmtUByte;  break;
@@ -141,17 +143,20 @@ void Sdl2Backend::open(const char *name)
     case AUDIO_S32SYS: mDevice->FmtType = DevFmtInt;    break;
     case AUDIO_F32SYS: mDevice->FmtType = DevFmtFloat;  break;
     default:
+        SDL_CloseAudioDevice(devid);
         throw al::backend_exception{al::backend_error::DeviceError, "Unhandled SDL format: 0x%04x",
             have.format};
     }
-    mDevice->UpdateSize = have.samples;
-    mDevice->BufferSize = have.samples * 2; /* SDL always (tries to) use two periods. */
 
-    mFrameSize = mDevice->frameSizeFromFmt();
-    mFrequency = mDevice->Frequency;
-    mFmtChans = mDevice->FmtChans;
-    mFmtType = mDevice->FmtType;
-    mUpdateSize = mDevice->UpdateSize;
+    if(mDeviceID)
+        SDL_CloseAudioDevice(mDeviceID);
+    mDeviceID = devid;
+
+    mFrameSize = FrameSizeFromDevFmt(devchans, devtype, 0);
+    mFrequency = static_cast<uint>(have.freq);
+    mFmtChans = devchans;
+    mFmtType = devtype;
+    mUpdateSize = have.samples;
 
     mDevice->DeviceName = name ? name : defaultDeviceName;
 }
@@ -162,7 +167,7 @@ bool Sdl2Backend::reset()
     mDevice->FmtChans = mFmtChans;
     mDevice->FmtType = mFmtType;
     mDevice->UpdateSize = mUpdateSize;
-    mDevice->BufferSize = mUpdateSize * 2;
+    mDevice->BufferSize = mUpdateSize * 2; /* SDL always (tries to) use two periods. */
     setDefaultWFXChannelOrder();
     return true;
 }