Support audio pauses

When the Linux console is e.g. switched to a graphical VT, the kernel
emits \x01P to notify that it is not able to read the screen any more,
and the software synthesis can thus release the audio card, for other
screen readers to take over.

This implements it by adding a paused_espeak variable that tracks
whether we have suspended espeak.  When more text comes, we can simply
reinitialize espeak.

espeak.c

@@ -40,6 +40,7 @@ const int rateOffset = 80;
 const int volumeMultiplier = 22;
 
 volatile int stop_requested = 0;
+int paused_espeak = 1;
 
 static int acsint_callback(short *wav, int numsamples, espeak_EVENT * events)
 {
@@ -211,6 +212,32 @@ static void synth_queue_clear()
 	}
 }
 
+static void reinitialize_espeak(struct synth_t *s)
+{
+	int rate;
+
+	/* Re-initialize espeak */
+	rate = espeak_Initialize(AUDIO_OUTPUT_PLAYBACK, 50, NULL, 0);
+	if (rate < 0) {
+		fprintf(stderr, "Unable to initialize espeak.\n");
+		return;
+	}
+
+	/* We need a callback in acsint mode, but not in speakup mode. */
+	if (espeakup_mode == ESPEAKUP_MODE_ACSINT)
+		espeak_SetSynthCallback(acsint_callback);
+
+	/* Set parameters again */
+	espeak_SetVoiceByName(s->voice);
+	espeak_SetParameter(espeakRANGE, s->frequency * frequencyMultiplier, 0);
+	espeak_SetParameter(espeakPITCH, s->pitch * pitchMultiplier, 0);
+	espeak_SetParameter(espeakRATE, s->rate * rateMultiplier + rateOffset, 0);
+	espeak_SetParameter(espeakVOLUME, (s->volume + 1) * volumeMultiplier, 0);
+	espeak_SetParameter(espeakCAPITALS, 0, 0);
+	paused_espeak = 0;
+	return;
+}
+
 static void queue_process_entry(struct synth_t *s)
 {
 	espeak_ERROR error;
@@ -222,6 +249,11 @@ static void queue_process_entry(struct synth_t *s)
 		current = (struct espeak_entry_t *) queue_remove(synth_queue);
 	}
 	pthread_mutex_unlock(&queue_guard);
+
+	if (current->cmd != CMD_PAUSE && paused_espeak) {
+		reinitialize_espeak(s);
+	}
+
 	switch (current->cmd) {
 	case CMD_SET_FREQUENCY:
 		error = set_frequency(s, current->value, current->adjust);
@@ -246,6 +278,13 @@ static void queue_process_entry(struct synth_t *s)
 		s->len = current->len;
 		error = speak_text(s);
 		break;
+	case CMD_PAUSE:
+		if (!paused_espeak) {
+			espeak_Cancel();
+			espeak_Terminate();
+			paused_espeak = 1;
+		}
+		break;
 	default:
 		break;
 	}
@@ -282,6 +321,7 @@ int initialize_espeak(struct synth_t *s)
 	set_rate(s, defaultRate, ADJ_SET);
 	set_volume(s, defaultVolume, ADJ_SET);
 	espeak_SetParameter(espeakCAPITALS, 0, 0);
+	paused_espeak = 0;
 	return 0;
 }
 

espeakup.c

@@ -231,7 +231,8 @@ int main(int argc, char **argv)
 	pthread_join(softsynth_thread_id, NULL);
 	pthread_join(espeak_thread_id, NULL);
 
-	espeak_Terminate();
+	if (!paused_espeak)
+		espeak_Terminate();
 	close_softsynth();
 
 out:

espeakup.h

@@ -45,6 +45,7 @@ enum command_t {
 	CMD_SET_VOLUME,
 	CMD_SPEAK_TEXT,
 	CMD_FLUSH,
+	CMD_PAUSE,
 	CMD_UNKNOWN,
 };
 
@@ -86,6 +87,7 @@ extern void close_softsynth(void);
 extern void *softsynth_thread(void *arg);
 extern volatile int should_run;
 extern volatile int stop_requested;
+extern int paused_espeak;
 extern int self_pipe_fds[2];
 #define PIPE_READ_FD (self_pipe_fds[0])
 #define PIPE_WRITE_FD (self_pipe_fds[1])

softsynth.c

@@ -133,6 +133,9 @@ static int process_command(struct synth_t *s, char *buf, int start)
 		case 'v':
 			cmd = CMD_SET_VOLUME;
 			break;
+		case 'P':
+			cmd = CMD_PAUSE;
+			break;
 		default:
 			cmd = CMD_UNKNOWN;
 			break;