Separates zone audio to different channels in car emulator

- rear seat buses (with "rear" in its address) uses right channel
- left channel otherwise

This behavior is enabled only if ro.aae.simulateMultiZoneAudio property
is turned on. To switch the behavior back and forth during runtime, one
has to restart the audioserver as well as car service after changing the
value via `adb shell setprop <key> <value>`. The most convenient way
would be to enable this flag at boot time as following

```
emulator -prop ro.aae.simulateMultiZoneAudio=true
```

Bug: 120299880
Test: manually on gcar_emu_x86-userdebug emulator
Change-Id: I61e542ca621f922dfafe7c5979bd4d13ab2fc57a

2 files changed, 31 insertions, 6 deletions

diff --git a/emulator/audio/driver/audio_hw.c b/emulator/audio/driver/audio_hw.c
index b1297cf..4e437bd 100644
--- a/emulator/audio/driver/audio_hw.c
+++ b/emulator/audio/driver/audio_hw.c
@@ -33,6 +33,7 @@
 #include <unistd.h>
 
 #include <log/log.h>
+#include <cutils/properties.h>
 #include <cutils/str_parms.h>
 
 #include <hardware/hardware.h>
@@ -52,6 +53,8 @@
 
 #define _bool_str(x) ((x)?"true":"false")
 
+#define PROP_KEY_SIMULATE_MULTI_ZONE_AUDIO "ro.aae.simulateMultiZoneAudio"
+
 static int adev_get_mic_mute(const struct audio_hw_device *dev, bool *state);
 
 static struct pcm_config pcm_config_out = {
@@ -118,6 +121,7 @@ static int out_dump(const struct audio_stream *stream, int fd) {
                 "\t\tformat: %d\n"
                 "\t\tdevice: %08x\n"
                 "\t\tamplitude ratio: %f\n"
+                "\t\tenabled channels: %d\n"
                 "\t\taudio dev: %p\n\n",
                 out->bus_address,
                 out_get_sample_rate(stream),
@@ -126,6 +130,7 @@ static int out_dump(const struct audio_stream *stream, int fd) {
                 out_get_format(stream),
                 out->device,
                 out->amplitude_ratio,
+                out->enabled_channels,
                 out->dev);
     pthread_mutex_unlock(&out->lock);
     return 0;
@@ -314,15 +319,21 @@ static void get_current_output_position(struct generic_stream_out *out,
     }
 }
 
-// Applies gain naively, assume AUDIO_FORMAT_PCM_16_BIT
+// Applies gain naively, assumes AUDIO_FORMAT_PCM_16_BIT and stereo output
 static void out_apply_gain(struct generic_stream_out *out, const void *buffer, size_t bytes) {
     int16_t *int16_buffer = (int16_t *)buffer;
     size_t int16_size = bytes / sizeof(int16_t);
     for (int i = 0; i < int16_size; i++) {
-         float multiplied = int16_buffer[i] * out->amplitude_ratio;
-         if (multiplied > INT16_MAX) int16_buffer[i] = INT16_MAX;
-         else if (multiplied < INT16_MIN) int16_buffer[i] = INT16_MIN;
-         else int16_buffer[i] = (int16_t)multiplied;
+        if ((i % 2) && !(out->enabled_channels & RIGHT_CHANNEL)) {
+            int16_buffer[i] = 0;
+        } else if (!(i % 2) && !(out->enabled_channels & LEFT_CHANNEL)) {
+            int16_buffer[i] = 0;
+        } else {
+            float multiplied = int16_buffer[i] * out->amplitude_ratio;
+            if (multiplied > INT16_MAX) int16_buffer[i] = INT16_MAX;
+            else if (multiplied < INT16_MIN) int16_buffer[i] = INT16_MIN;
+            else int16_buffer[i] = (int16_t)multiplied;
+        }
     }
 }
 
@@ -526,7 +537,9 @@ static int refine_output_parameters(uint32_t *sample_rate, audio_format_t *forma
 
 static int refine_input_parameters(uint32_t *sample_rate, audio_format_t *format,
         audio_channel_mask_t *channel_mask) {
-    static const uint32_t sample_rates [] = {8000, 11025, 16000, 22050, 44100, 48000};
+    static const uint32_t sample_rates [] = {
+        8000, 11025, 16000, 22050, 44100, 48000
+    };
     static const int sample_rates_count = sizeof(sample_rates)/sizeof(uint32_t);
     bool inval = false;
     // Only PCM_16_bit is supported. If this is changed, stereo to mono drop
@@ -1006,6 +1019,7 @@ static int adev_open_output_stream(struct audio_hw_device *dev,
         pthread_create(&out->worker_thread, NULL, out_write_worker, out);
     }
 
+    out->enabled_channels = BOTH_CHANNELS;
     if (address) {
         out->bus_address = calloc(strlen(address) + 1, sizeof(char));
         strncpy(out->bus_address, address, strlen(address));
@@ -1017,6 +1031,10 @@ static int adev_open_output_stream(struct audio_hw_device *dev,
             .step_value = 100,
         };
         out->amplitude_ratio = 1.0;
+        if (property_get_bool(PROP_KEY_SIMULATE_MULTI_ZONE_AUDIO, false)) {
+            out->enabled_channels = strstr(out->bus_address, "rear")
+                ? RIGHT_CHANNEL: LEFT_CHANNEL;
+        }
     }
     *stream_out = &out->stream;
     ALOGD("%s bus:%s", __func__, out->bus_address);
diff --git a/emulator/audio/driver/audio_hw.h b/emulator/audio/driver/audio_hw.h
index 21eda66..903a9b8 100644
--- a/emulator/audio/driver/audio_hw.h
+++ b/emulator/audio/driver/audio_hw.h
@@ -35,6 +35,12 @@ struct generic_audio_device {
   Hashmap *out_bus_stream_map;  // Extended field. Constant after init
 };
 
+enum output_channel_enable {
+  LEFT_CHANNEL = 1,
+  RIGHT_CHANNEL = 1 << 1,
+  BOTH_CHANNELS = LEFT_CHANNEL | RIGHT_CHANNEL
+};
+
 struct generic_stream_out {
   struct audio_stream_out stream;  // Constant after init
   pthread_mutex_t lock;
@@ -46,6 +52,7 @@ struct generic_stream_out {
   const char *bus_address;           // Extended field. Constant after init
   struct audio_gain gain_stage;      // Constant after init
   float amplitude_ratio;             // Protected by this->lock
+  enum output_channel_enable enabled_channels;  // Constant after init
 
   // Time & Position Keeping
   bool standby;                    // Protected by this->lock