OpenDingux: Improve fast-forwarding. Better detection of the need to increase frame skipping when there is insufficient buffered audio, and to raise the frame rate again once a fair amount of time has passed without audio underruns. This may help the Dingoo A320.

7 files changed, 83 insertions, 53 deletions

diff --git a/source/opendingux/draw.c b/source/opendingux/draw.c
index 8427295..bc47a29 100644
--- a/source/opendingux/draw.c
+++ b/source/opendingux/draw.c
@@ -22,9 +22,10 @@
 uint16_t* GBAScreen;
 uint32_t  GBAScreenPitch = GBA_SCREEN_WIDTH;
 
-volatile uint_fast8_t VideoFastForwarded;
+volatile unsigned int VideoFastForwarded;
 uint_fast8_t AudioFrameskip = 0;
 uint_fast8_t AudioFrameskipControl = 0;
+uint_fast8_t SufficientAudioControl = 0;
 uint_fast8_t UserFrameskipControl = 0;
 
 uint_fast8_t FramesBordered = 0;
@@ -557,10 +558,15 @@ void ReGBA_RenderScreen(void)
 
 		SDL_Flip(OutputSurface);
 
-		while (ReGBA_GetAudioSamplesAvailable() > AUDIO_OUTPUT_BUFFER_SIZE * 3 * OUTPUT_FREQUENCY_DIVISOR + (VideoFastForwarded - AudioFastForwarded) * ((int) (SOUND_FREQUENCY / 59.73)))
+		while (true)
 		{
-			if (AudioFrameskip > 0)
-				AudioFrameskip--;
+			unsigned int AudioFastForwardedCopy = AudioFastForwarded;
+			unsigned int FramesAhead = (VideoFastForwarded >= AudioFastForwardedCopy)
+				? /* no overflow */ VideoFastForwarded - AudioFastForwardedCopy
+				: /* overflow */    0x100 - (AudioFastForwardedCopy - VideoFastForwarded);
+			uint32_t Quota = AUDIO_OUTPUT_BUFFER_SIZE * 3 * OUTPUT_FREQUENCY_DIVISOR + (uint32_t) (FramesAhead * (SOUND_FREQUENCY / 59.73f));
+			if (ReGBA_GetAudioSamplesAvailable() <= Quota)
+				break;
 			usleep(1000);
 		}
 	}
@@ -569,29 +575,40 @@ void ReGBA_RenderScreen(void)
 	{
 		if (AudioFrameskip < MAX_AUTO_FRAMESKIP)
 			AudioFrameskip++;
+		SufficientAudioControl = 0;
+	}
+	else
+	{
+		SufficientAudioControl++;
+		if (SufficientAudioControl >= 10)
+		{
+			SufficientAudioControl = 0;
+			if (AudioFrameskip > 0)
+				AudioFrameskip--;
+		}
 	}
 
-	if (FastForwardControl >= 60)
+	if (FastForwardFrameskip > 0 && FastForwardFrameskipControl > 0)
 	{
-		FastForwardControl -= 60;
-		VideoFastForwarded++;
+		FastForwardFrameskipControl--;
+		VideoFastForwarded = (VideoFastForwarded + 1) & 0xFF;
+	}
+	else
+	{
+		FastForwardFrameskipControl = FastForwardFrameskip;
+		if (UserFrameskip != 0)
+		{
+			if (UserFrameskipControl == 0)
+				UserFrameskipControl = UserFrameskip - 1;
+			else
+				UserFrameskipControl--;
+		}
 	}
-	FastForwardControl += FastForwardValue;
 
 	if (AudioFrameskipControl > 0)
 		AudioFrameskipControl--;
-	else if (AudioFrameskipControl == 0)
+	else
 		AudioFrameskipControl = AudioFrameskip;
-
-	if (UserFrameskip != 0)
-	{
-		if (UserFrameskipControl == 0)
-			UserFrameskipControl = UserFrameskip - 1;
-		else
-			UserFrameskipControl--;
-		if (FastForwardControl < 60 && FastForwardValue + FastForwardControl >= 60)
-			UserFrameskipControl = 0; // allow fast-forwarding even at FS 0
-	}
 }
 
 u16 *copy_screen()
diff --git a/source/opendingux/draw.h b/source/opendingux/draw.h
index b0fae4d..aeea56d 100644
--- a/source/opendingux/draw.h
+++ b/source/opendingux/draw.h
@@ -15,6 +15,10 @@ extern uint_fast8_t AudioFrameskip;
 extern uint_fast8_t AudioFrameskipControl;
 extern uint_fast8_t UserFrameskipControl;
 
+// Incremented by the video thread when it decides to skip a frame due to
+// fast forwarding.
+extern volatile unsigned int VideoFastForwarded;
+
 // How many back buffers have had ApplyScaleMode called upon them?
 // At 3, even a triple-buffered surface has had ApplyScaleMode called on
 // all back buffers, so stopping remanence with ApplyScaleMode is wasteful.
diff --git a/source/opendingux/od-input.c b/source/opendingux/od-input.c
index 0f244a8..a657e77 100644
--- a/source/opendingux/od-input.c
+++ b/source/opendingux/od-input.c
@@ -19,11 +19,11 @@
 
 #include "common.h"
 
-uint_fast8_t FastForwardValue = 0;
+uint_fast8_t FastForwardFrameskip = 0;
 
 uint32_t FastForwardTarget = 4; // 6x by default
 
-uint_fast8_t FastForwardControl = 0;
+uint_fast8_t FastForwardFrameskipControl = 0;
 
 static SDL_Joystick* Joystick;
 
@@ -145,8 +145,8 @@ static void UpdateOpenDinguxButtons()
 
 void ProcessSpecialKeys()
 {
-	FastForwardValue = (Hotkeys[0] != 0 && (Hotkeys[0] & LastButtons) == Hotkeys[0])
-		? 60 - (60 / (2 + FastForwardTarget))
+	FastForwardFrameskip = (Hotkeys[0] != 0 && (Hotkeys[0] & LastButtons) == Hotkeys[0])
+		? FastForwardTarget + 1
 		: 0;
 }
 
diff --git a/source/opendingux/od-input.h b/source/opendingux/od-input.h
index a01680a..431bb8b 100644
--- a/source/opendingux/od-input.h
+++ b/source/opendingux/od-input.h
@@ -49,30 +49,21 @@ enum GUI_Action {
 };
 
 // 0 if not fast-forwarding.
-// Otherwise, the amount of frames to skip per second.
-// 30 amounts to targetting 200% real-time;
-// 40 amounts to targetting 300% real-time;
-// 45 amounts to targetting 400% real-time;
-// 48 amounts to targetting 500% real-time;
-// 50 amounts to targetting 600% real-time.
-extern uint_fast8_t FastForwardValue;
-
-// The number of times to target while fast-forwarding. (UI option)
+// Otherwise, the amount of frames to skip per rendered frame.
+// 1 amounts to targetting 200% real-time;
+// 2 amounts to targetting 300% real-time;
+// 3 amounts to targetting 400% real-time;
+// 4 amounts to targetting 500% real-time;
+// 5 amounts to targetting 600% real-time.
+extern uint_fast8_t FastForwardFrameskip;
+
+// The number of times to target while fast-forwarding is enabled. (UI option)
 // 0 means 2x, 1 means 3x, ... 4 means 6x.
 extern uint32_t FastForwardTarget;
 
-// Incremented by FastForwardValue every frame. If it's over 60,
-// a frame is skipped, 60 is removed, then FastForwardValue is added again.
-extern uint_fast8_t FastForwardControl;
-
-// Incremented by the video thread when it decides to skip a frame due to
-// fast forwarding.
-extern volatile uint_fast8_t VideoFastForwarded;
-
-// Modified by the audio thread to match VideoFastForwarded after it finds
-// that the video thread has skipped a frame. The audio thread must deal
-// with the condition as soon as possible.
-extern volatile uint_fast8_t AudioFastForwarded;
+// If this is greater than 0, a frame and its audio are skipped.
+// The value then goes to FastForwardFrameskip and is decremented until 0.
+extern uint_fast8_t FastForwardFrameskipControl;
 
 /*
  * Gets the current value of the analog horizontal axis.
diff --git a/source/opendingux/od-sound.c b/source/opendingux/od-sound.c
index 4354136..d7e237d 100644
--- a/source/opendingux/od-sound.c
+++ b/source/opendingux/od-sound.c
@@ -3,7 +3,7 @@
 #include "common.h"
 #include "../sound.h"
 
-volatile uint_fast8_t AudioFastForwarded;
+volatile unsigned int AudioFastForwarded;
 
 #define DAMPEN_SAMPLE_COUNT (AUDIO_OUTPUT_BUFFER_SIZE / 32)
 
@@ -65,12 +65,17 @@ void feed_buffer(void *udata, Uint8 *buffer, int len)
 	}
 	Samples -= Requested / 2;
 	
-	// Discard sound until half the requested length is left, if fast-forwarding.
+	// Discard as many samples as are generated in 1 frame, if fast-forwarding.
 	bool Skipped = false;
-	uint_fast8_t VideoFastForwardedCopy = VideoFastForwarded;
+	unsigned int VideoFastForwardedCopy = VideoFastForwarded;
 	if (VideoFastForwardedCopy != AudioFastForwarded)
 	{
-		uint32_t SamplesToSkip = Samples - (Requested * 3 - Requested / 2);
+		unsigned int FramesToSkip = (VideoFastForwardedCopy > AudioFastForwarded)
+			? /* no overflow */ VideoFastForwardedCopy - AudioFastForwarded
+			: /* overflow */    0x100 - (AudioFastForwarded - VideoFastForwardedCopy);
+		uint32_t SamplesToSkip = (uint32_t) (FramesToSkip * (OUTPUT_SOUND_FREQUENCY / 59.73f));
+		if (SamplesToSkip > Samples - (Requested * 3 - Requested / 2))
+			SamplesToSkip = Samples - (Requested * 3 - Requested / 2);
 		ReGBA_DiscardAudioSamples(SamplesToSkip * OUTPUT_FREQUENCY_DIVISOR);
 		Samples -= SamplesToSkip;
 		AudioFastForwarded = VideoFastForwardedCopy;
diff --git a/source/opendingux/od-sound.h b/source/opendingux/od-sound.h
index 2cf42a4..1921856 100644
--- a/source/opendingux/od-sound.h
+++ b/source/opendingux/od-sound.h
@@ -3,7 +3,10 @@
 
 void init_sdlaudio();
 
-extern int audio_discardflag;
+// Modified by the audio thread to match VideoFastForwarded after it finds
+// that the video thread has skipped a frame. The audio thread must deal
+// with the condition as soon as possible.
+extern volatile unsigned int AudioFastForwarded;
 
 #define AUDIO_OUTPUT_BUFFER_SIZE 1476
 
diff --git a/source/opendingux/port.c b/source/opendingux/port.c
index 6fd4229..70e9844 100644
--- a/source/opendingux/port.c
+++ b/source/opendingux/port.c
@@ -133,10 +133,20 @@ void ReGBA_LoadRTCTime(struct ReGBA_RTC* RTCData)
 
 bool ReGBA_IsRenderingNextFrame()
 {
-	if (UserFrameskip == 0) /* automatic */
-		return FastForwardControl < 60 && AudioFrameskipControl == 0;
-
-	return FastForwardControl < 60 && UserFrameskipControl == 0; /* manual, draw this frame */
+	if (FastForwardFrameskip != 0) /* fast-forwarding */
+	{
+		if (UserFrameskip != 0)  /* fast-forwarding on user frameskip */
+			return FastForwardFrameskipControl == 0 && UserFrameskipControl == 0;
+		else /* fast-forwarding on automatic frameskip */
+			return FastForwardFrameskipControl == 0 && AudioFrameskipControl == 0;
+	}
+	else
+	{
+		if (UserFrameskip != 0) /* user frameskip */
+			return UserFrameskipControl == 0;
+		else /* automatic frameskip */
+			return AudioFrameskipControl == 0;
+	}
 }
 
 const char* GetFileName(const char* Path)