Greatly reduce audio latency, remove popping sound when loading saves

Author: garrettgu10

src/org/the429ers/gameboy/GameBoy.java

@@ -7,6 +7,7 @@
 import java.text.SimpleDateFormat;
 import java.util.*;
 
+import javax.sound.sampled.SourceDataLine;
 import javax.swing.*;
 
 class MainMenuBar extends MenuBar {
@@ -223,6 +224,8 @@ public class GameBoy extends JFrame{
     InputStream loadFile = null;
     LinkedList<ByteArrayOutputStream> autoSaves = new LinkedList<>();
 
+    SourceDataLine sourceDL;
+    
     private static GameBoy gb;
 
     public static GameBoy getInstance() {
@@ -255,6 +258,7 @@ public void windowOpened(WindowEvent e) { }
     };
 
     public void switchRom(String newRom) {
+        this.sourceDL = mmu.soundChip.getSourceDL();
         this.romFileName = newRom;
         if(mmu != null) mmu.cleanUp();
         mmu = new MMU(newRom);
@@ -271,11 +275,10 @@ public void switchRom(String newRom) {
             ppu = new PPU(mmu, gbs);
         }
         mmu.setPPU(ppu);
+        mmu.soundChip.setSourceDL(this.sourceDL);
         cable = new LinkCable(mmu, cpu.interruptHandler);
         joypad = new Joypad(mmu, cpu.interruptHandler);
         gbs.addKeyListener(joypad);
-
-
     }
 
     public GameBoy(String fileName) {
@@ -317,6 +320,7 @@ public GameBoy(String fileName) {
     }
 
     public void saveState() {
+        this.sourceDL = this.mmu.soundChip.getSourceDL();
         try {
             ObjectOutputStream saveState = new ObjectOutputStream(this.saveFile);
             saveState.writeObject(mmu);
@@ -351,6 +355,7 @@ public void loadState() {
         }
         gbs.addKeyListener(this.mmu.getJoypad());
         ppu.setGBS(gbs);
+        this.mmu.soundChip.setSourceDL(this.sourceDL);
     }
 
     public void tick() {

src/org/the429ers/gameboy/SoundChannel.java

@@ -28,10 +28,12 @@ class SoundChip implements Serializable {
     public static final int WAVE = 2;
     public static final int NOISE = 3;
 
-    private transient SourceDataLine sourceDL;
+    transient SourceDataLine sourceDL;
 
-    byte[] masterBuffer = new byte[2 * SAMPLES_PER_FRAME];
-    byte[] tempBuffer = new byte[SAMPLES_PER_FRAME];
+    byte[] masterBuffer = new byte[6 * SAMPLES_PER_FRAME];
+    byte[] tempBuffer = new byte[3 * SAMPLES_PER_FRAME];
+    
+    long totalSamplesWritten = 0;
 
     boolean[] leftEnabled = new boolean[4];
     boolean[] rightEnabled = new boolean[4];
@@ -40,16 +42,13 @@ class SoundChip implements Serializable {
         Arrays.fill(rightEnabled, true);
     }
 
-    private void readObject(ObjectInputStream in) throws IOException, ClassNotFoundException {
-        in.defaultReadObject();
-
-        try {
-            sourceDL = AudioSystem.getSourceDataLine(AUDIO_FORMAT);
-            sourceDL.open(AUDIO_FORMAT);
-            sourceDL.start();
-        } catch (LineUnavailableException e) {
-            e.printStackTrace();
-        }
+    public void setSourceDL(SourceDataLine sourceDL){
+        this.sourceDL = sourceDL;
+        this.totalSamplesWritten = sourceDL.getLongFramePosition();
+    }
+    
+    public SourceDataLine getSourceDL(){
+        return this.sourceDL;
     }
 
     SoundChip() {
@@ -82,7 +81,10 @@ public void tick() {
                 e.printStackTrace();
             }
         }
-        int samplesToWrite = Math.min(sourceDL.available() / 3, SAMPLES_PER_FRAME);
+        long residualSamples = totalSamplesWritten - sourceDL.getLongFramePosition();
+        int samplesToWrite = Math.max(0, (int)(3 * SAMPLES_PER_FRAME - residualSamples)); //try to keep 3 frames buffered at all times
+        samplesToWrite = Math.min(sourceDL.available() / 2, Math.min(3 * SAMPLES_PER_FRAME, samplesToWrite)); //never want to block here
+        totalSamplesWritten += samplesToWrite;
 
         Arrays.fill(masterBuffer, (byte) 0);