Implement rewind screen and logic

Currently, rewind is always enabled and with hardcoded values. Adding settings for these configurations is still required.

app/build.gradle.kts

@@ -74,6 +74,7 @@ android {
         }
     }
     compileOptions {
+        isCoreLibraryDesugaringEnabled = true
     }
     configurations.all {
         resolutionStrategy.eachDependency {
@@ -90,6 +91,10 @@ android {
 dependencies {
     val gitHubImplementation by configurations
 
+    with(Dependencies.Tools) {
+        coreLibraryDesugaring(desugarJdkLibs)
+    }
+
     with(Dependencies.Kotlin) {
         implementation(kotlinStdlib)
     }

app/proguard-rules.pro

@@ -31,6 +31,8 @@
 -keep class me.magnum.melonds.domain.model.ConsoleType { *; }
 -keep class me.magnum.melonds.domain.model.MicSource { *; }
 -keep class me.magnum.melonds.domain.model.Cheat { *; }
+-keep class me.magnum.melonds.ui.emulator.rewind.model.RewindSaveState { *; }
+-keep class me.magnum.melonds.ui.emulator.rewind.model.RewindWindow { *; }
 -keep class me.magnum.melonds.ui.settings.fragments.**
 -keep class me.magnum.melonds.common.UriFileHandler {
     public int open(java.lang.String, java.lang.String);

app/src/main/cpp/MelonDSAndroidJNI.cpp

@@ -267,6 +267,79 @@ Java_me_magnum_melonds_MelonEmulator_loadStateInternal(JNIEnv* env, jobject thiz
     return MelonDSAndroid::loadState(saveStatePath);
 }
 
+JNIEXPORT jboolean JNICALL
+Java_me_magnum_melonds_MelonEmulator_loadRewindState(JNIEnv* env, jobject thiz, jobject rewindSaveState) {
+    bool result = true;
+
+    pthread_mutex_lock(&emuThreadMutex);
+    if (!stop) {
+        bool wasPaused = paused;
+        if (paused) {
+            pthread_mutex_unlock(&emuThreadMutex);
+        } else {
+            pthread_mutex_unlock(&emuThreadMutex);
+            Java_me_magnum_melonds_MelonEmulator_pauseEmulation(env, thiz);
+        }
+
+        jclass rewindSaveStateClass = env->FindClass("me/magnum/melonds/ui/emulator/rewind/model/RewindSaveState");
+        jfieldID bufferField = env->GetFieldID(rewindSaveStateClass, "buffer", "Ljava/nio/ByteBuffer;");
+        jfieldID screenshotBufferField = env->GetFieldID(rewindSaveStateClass, "screenshotBuffer", "Ljava/nio/ByteBuffer;");
+        jfieldID frameField = env->GetFieldID(rewindSaveStateClass, "frame", "I");
+        jobject buffer = env->GetObjectField(rewindSaveState, bufferField);
+        jobject screenshotBuffer = env->GetObjectField(rewindSaveState, screenshotBufferField);
+        jint frame = (int) env->GetIntField(rewindSaveState, frameField);
+
+        // Make sure that the thread is really paused to avoid data corruption
+        while (!isThreadReallyPaused);
+
+        RewindManager::RewindSaveState state = RewindManager::RewindSaveState {
+            .buffer = (u8*) env->GetDirectBufferAddress(buffer),
+            .bufferSize = (u32) env->GetDirectBufferCapacity(buffer),
+            .screenshot = (u8*) env->GetDirectBufferAddress(screenshotBuffer),
+            .screenshotSize = (u32) env->GetDirectBufferCapacity(screenshotBuffer),
+            .frame = frame
+        };
+
+        result = MelonDSAndroid::loadRewindState(state);
+
+        // Resume emulation if it was running
+        if (!wasPaused) {
+            Java_me_magnum_melonds_MelonEmulator_resumeEmulation(env, thiz);
+        }
+    } else {
+        // If the emulation is stopping, just ignore it
+        pthread_mutex_unlock(&emuThreadMutex);
+    }
+
+    return result;
+}
+
+JNIEXPORT jobject JNICALL
+Java_me_magnum_melonds_MelonEmulator_getRewindWindow(JNIEnv* env, jobject thiz) {
+    auto currentRewindWindow = MelonDSAndroid::getRewindWindow();
+
+    jclass rewindSaveStateClass = env->FindClass("me/magnum/melonds/ui/emulator/rewind/model/RewindSaveState");
+    jmethodID rewindSaveStateConstructor = env->GetMethodID(rewindSaveStateClass, "<init>", "(Ljava/nio/ByteBuffer;Ljava/nio/ByteBuffer;I)V");
+
+    jclass listClass = env->FindClass("java/util/ArrayList");
+    jmethodID listConstructor = env->GetMethodID(listClass, "<init>", "()V");
+    jmethodID listAddMethod = env->GetMethodID(listClass, "add", "(ILjava/lang/Object;)V");
+    jobject rewindStateList = env->NewObject(listClass, listConstructor);
+
+    int index = 0;
+    for (auto state : currentRewindWindow.rewindStates) {
+        jobject stateBuffer = env->NewDirectByteBuffer(state.buffer, state.bufferSize);
+        jobject stateScreenshot = env->NewDirectByteBuffer(state.screenshot, state.screenshotSize);
+        jobject rewindSaveState = env->NewObject(rewindSaveStateClass, rewindSaveStateConstructor, stateBuffer, stateScreenshot, state.frame);
+        env->CallVoidMethod(rewindStateList, listAddMethod, index++, rewindSaveState);
+    }
+
+    jclass rewindWindowClass = env->FindClass("me/magnum/melonds/ui/emulator/rewind/model/RewindWindow");
+    jmethodID rewindWindowConstructor = env->GetMethodID(rewindWindowClass, "<init>", "(ILjava/util/ArrayList;)V");
+    jobject rewindWindow = env->NewObject(rewindWindowClass, rewindWindowConstructor, currentRewindWindow.currentFrame, rewindStateList);
+    return rewindWindow;
+}
+
 JNIEXPORT void JNICALL
 Java_me_magnum_melonds_MelonEmulator_stopEmulation(JNIEnv* env, jobject thiz)
 {
@@ -414,6 +487,9 @@ MelonDSAndroid::EmulatorConfiguration buildEmulatorConfiguration(JNIEnv* env, jo
     finalEmulatorConfiguration.micSource = micSource;
     finalEmulatorConfiguration.firmwareConfiguration = buildFirmwareConfiguration(env, firmwareConfigurationObject);
     finalEmulatorConfiguration.renderSettings = buildRenderSettings(env, rendererConfigurationObject);
+    finalEmulatorConfiguration.rewindEnabled = 1;
+    finalEmulatorConfiguration.rewindCaptureSpacingSeconds = 2;
+    finalEmulatorConfiguration.rewindLengthSeconds = 30;
     return finalEmulatorConfiguration;
 }
 

app/src/main/java/me/magnum/melonds/MelonEmulator.kt

@@ -6,6 +6,8 @@ import me.magnum.melonds.domain.model.Cheat
 import me.magnum.melonds.domain.model.EmulatorConfiguration
 import me.magnum.melonds.domain.model.Input
 import me.magnum.melonds.common.UriFileHandler
+import me.magnum.melonds.ui.emulator.rewind.model.RewindSaveState
+import me.magnum.melonds.ui.emulator.rewind.model.RewindWindow
 import java.nio.ByteBuffer
 
 object MelonEmulator {
@@ -81,6 +83,10 @@ object MelonEmulator {
 
     private external fun loadStateInternal(path: String): Boolean
 
+    external fun loadRewindState(rewindSaveState: RewindSaveState): Boolean
+
+    external fun getRewindWindow(): RewindWindow
+
 	external fun onScreenTouch(x: Int, y: Int)
 
 	external fun onScreenRelease()

app/src/main/java/me/magnum/melonds/ui/emulator/EmulatorActivity.kt

@@ -17,8 +17,10 @@ import androidx.activity.result.contract.ActivityResultContracts
 import androidx.activity.viewModels
 import androidx.appcompat.app.AlertDialog
 import androidx.appcompat.app.AppCompatActivity
+import androidx.constraintlayout.widget.ConstraintLayout
 import androidx.core.net.toUri
 import androidx.core.view.*
+import androidx.recyclerview.widget.LinearLayoutManager
 import com.squareup.picasso.Picasso
 import dagger.hilt.android.AndroidEntryPoint
 import io.reactivex.Single
@@ -42,6 +44,9 @@ import me.magnum.melonds.ui.cheats.CheatsActivity
 import me.magnum.melonds.ui.emulator.DSRenderer.RendererListener
 import me.magnum.melonds.ui.emulator.firmware.FirmwareEmulatorDelegate
 import me.magnum.melonds.ui.emulator.input.*
+import me.magnum.melonds.ui.emulator.rewind.EdgeSpacingDecorator
+import me.magnum.melonds.ui.emulator.rewind.model.RewindSaveState
+import me.magnum.melonds.ui.emulator.rewind.RewindSaveStateAdapter
 import me.magnum.melonds.ui.emulator.rom.RomEmulatorDelegate
 import me.magnum.melonds.ui.settings.SettingsActivity
 import java.net.URLEncoder
@@ -160,6 +165,10 @@ class EmulatorActivity : AppCompatActivity(), RendererListener {
         microphonePermissionSubject.onNext(it)
     }
 
+    private val rewindSaveStateAdapter = RewindSaveStateAdapter {
+        MelonEmulator.loadRewindState(it)
+        closeRewindWindow()
+    }
     private val microphonePermissionSubject = PublishSubject.create<Boolean>()
     private var emulatorSetupDisposable: Disposable? = null
     private var cheatsClosedListener: (() -> Unit)? = null
@@ -189,6 +198,15 @@ class EmulatorActivity : AppCompatActivity(), RendererListener {
 
         binding.textFps.visibility = View.INVISIBLE
         binding.viewLayoutControls.setLayoutComponentViewBuilderFactory(RuntimeLayoutComponentViewBuilderFactory())
+        binding.layoutRewind.setOnClickListener {
+            closeRewindWindow()
+        }
+        binding.listRewind.apply {
+            val listLayoutManager = LinearLayoutManager(context, LinearLayoutManager.HORIZONTAL, true)
+            layoutManager = listLayoutManager
+            addItemDecoration(EdgeSpacingDecorator())
+            adapter = rewindSaveStateAdapter
+        }
 
         viewModel.getBackground().observe(this) {
             dsRenderer.setBackground(it)
@@ -242,8 +260,9 @@ class EmulatorActivity : AppCompatActivity(), RendererListener {
         super.onResume()
         binding.surfaceMain.onResume()
 
-        if (emulatorReady && !emulatorPaused)
+        if (emulatorReady && !emulatorPaused) {
             MelonEmulator.resumeEmulation()
+        }
     }
 
     private fun launchEmulator() {
@@ -307,31 +326,33 @@ class EmulatorActivity : AppCompatActivity(), RendererListener {
             binding.textFps.isGone = true
         } else {
             binding.textFps.isVisible = true
-            val newParams = RelativeLayout.LayoutParams(RelativeLayout.LayoutParams.WRAP_CONTENT, RelativeLayout.LayoutParams.WRAP_CONTENT)
+            val newParams = ConstraintLayout.LayoutParams(RelativeLayout.LayoutParams.WRAP_CONTENT, RelativeLayout.LayoutParams.WRAP_CONTENT)
             when (fpsCounterPosition) {
                 FpsCounterPosition.TOP_LEFT -> {
-                    newParams.addRule(RelativeLayout.ALIGN_PARENT_LEFT)
-                    newParams.addRule(RelativeLayout.ALIGN_PARENT_TOP)
+                    newParams.topToTop = ConstraintLayout.LayoutParams.PARENT_ID
+                    newParams.leftToLeft = ConstraintLayout.LayoutParams.PARENT_ID
                 }
                 FpsCounterPosition.TOP_CENTER -> {
-                    newParams.addRule(RelativeLayout.CENTER_HORIZONTAL)
-                    newParams.addRule(RelativeLayout.ALIGN_PARENT_TOP)
+                    newParams.topToTop = ConstraintLayout.LayoutParams.PARENT_ID
+                    newParams.leftToLeft = ConstraintLayout.LayoutParams.PARENT_ID
+                    newParams.rightToRight = ConstraintLayout.LayoutParams.PARENT_ID
                 }
                 FpsCounterPosition.TOP_RIGHT -> {
-                    newParams.addRule(RelativeLayout.ALIGN_PARENT_RIGHT)
-                    newParams.addRule(RelativeLayout.ALIGN_PARENT_TOP)
+                    newParams.topToTop = ConstraintLayout.LayoutParams.PARENT_ID
+                    newParams.rightToRight = ConstraintLayout.LayoutParams.PARENT_ID
                 }
                 FpsCounterPosition.BOTTOM_LEFT -> {
-                    newParams.addRule(RelativeLayout.ALIGN_PARENT_LEFT)
-                    newParams.addRule(RelativeLayout.ALIGN_PARENT_BOTTOM)
+                    newParams.bottomToBottom = ConstraintLayout.LayoutParams.PARENT_ID
+                    newParams.leftToLeft = ConstraintLayout.LayoutParams.PARENT_ID
                 }
                 FpsCounterPosition.BOTTOM_CENTER -> {
-                    newParams.addRule(RelativeLayout.CENTER_HORIZONTAL)
-                    newParams.addRule(RelativeLayout.ALIGN_PARENT_BOTTOM)
+                    newParams.bottomToBottom = ConstraintLayout.LayoutParams.PARENT_ID
+                    newParams.leftToLeft = ConstraintLayout.LayoutParams.PARENT_ID
+                    newParams.rightToRight = ConstraintLayout.LayoutParams.PARENT_ID
                 }
                 FpsCounterPosition.BOTTOM_RIGHT -> {
-                    newParams.addRule(RelativeLayout.ALIGN_PARENT_RIGHT)
-                    newParams.addRule(RelativeLayout.ALIGN_PARENT_BOTTOM)
+                    newParams.bottomToBottom = ConstraintLayout.LayoutParams.PARENT_ID
+                    newParams.rightToRight = ConstraintLayout.LayoutParams.PARENT_ID
                 }
             }
             binding.textFps.layoutParams = newParams
@@ -443,7 +464,11 @@ class EmulatorActivity : AppCompatActivity(), RendererListener {
 
     override fun onBackPressed() {
         if (emulatorReady) {
-            this.pauseEmulation()
+            if (isRewindWindowOpen()) {
+                closeRewindWindow()
+            } else {
+                this.pauseEmulation()
+            }
         } else {
             super.onBackPressed()
         }
@@ -490,7 +515,7 @@ class EmulatorActivity : AppCompatActivity(), RendererListener {
     }
 
     override fun dispatchKeyEvent(event: KeyEvent): Boolean {
-        if (nativeInputListener.onKeyEvent(event))
+        if (!isRewindWindowOpen() && nativeInputListener.onKeyEvent(event))
             return true
 
         return super.dispatchKeyEvent(event)
@@ -520,6 +545,27 @@ class EmulatorActivity : AppCompatActivity(), RendererListener {
         cheatsLauncher.launch(intent)
     }
 
+    private fun isRewindWindowOpen(): Boolean {
+        return binding.root.currentState == R.id.rewind_visible
+    }
+
+    fun openRewindWindow() {
+        binding.root.transitionToState(R.id.rewind_visible)
+        val rewindWindow = MelonEmulator.getRewindWindow()
+        rewindSaveStateAdapter.setRewindWindow(rewindWindow)
+    }
+
+    fun closeRewindWindow() {
+        binding.root.transitionToState(R.id.rewind_hidden)
+        MelonEmulator.resumeEmulation()
+    }
+
+    fun rewindToState(state: RewindSaveState) {
+        if (!MelonEmulator.loadRewindState(state)) {
+            Toast.makeText(this@EmulatorActivity, "Failed to rewind", Toast.LENGTH_SHORT).show()
+        }
+    }
+
     /**
      * Returns a [Single] that emits the emulator's configuration taking into account permissions that have not been granted. If the provided base configuration requires the
      * use of certain permissions and [requestPermissions] is true, they will be requested to the user before returning the final configuration.
@@ -602,8 +648,9 @@ class EmulatorActivity : AppCompatActivity(), RendererListener {
         super.onPause()
         binding.surfaceMain.onPause()
 
-        if (emulatorReady && !emulatorPaused)
+        if (emulatorReady && !emulatorPaused) {
             MelonEmulator.pauseEmulation()
+        }
     }
 
     override fun onDestroy() {

app/src/main/java/me/magnum/melonds/ui/emulator/rewind/EdgeSpacingDecorator.kt

@@ -0,0 +1,38 @@
+package me.magnum.melonds.ui.emulator.rewind
+
+import android.graphics.Rect
+import android.view.View
+import androidx.core.view.marginLeft
+import androidx.core.view.marginRight
+import androidx.recyclerview.widget.RecyclerView
+
+/**
+ * [RecyclerView.ItemDecoration] that adds spacing to the edge views so that these items always appear centered in the view. Only works for horizontal lists.
+ */
+class EdgeSpacingDecorator : RecyclerView.ItemDecoration() {
+
+    override fun getItemOffsets(outRect: Rect, view: View, parent: RecyclerView, state: RecyclerView.State) {
+        super.getItemOffsets(outRect, view, parent, state)
+
+        val position = parent.getChildAdapterPosition(view)
+        if (position == 0) {
+            val offset = getEdgeViewOffset(view, parent)
+            outRect.right = offset
+        } else if (position == state.itemCount - 1) {
+            val offset = getEdgeViewOffset(view, parent)
+            outRect.left = offset
+        }
+    }
+
+    private fun getEdgeViewOffset(view: View, parent: RecyclerView): Int {
+        val viewWidth = if (view.width == 0) {
+            // View size still unknown. Measure it
+            view.measure(View.MeasureSpec.UNSPECIFIED, View.MeasureSpec.UNSPECIFIED)
+            view.measuredWidth
+        } else {
+            view.width
+        }
+
+        return (parent.width - viewWidth - view.marginLeft - view.marginRight) / 2
+    }
+}

app/src/main/java/me/magnum/melonds/ui/emulator/rewind/RewindSaveStateAdapter.kt

@@ -0,0 +1,97 @@
+package me.magnum.melonds.ui.emulator.rewind
+
+import android.content.Context
+import android.graphics.drawable.BitmapDrawable
+import android.view.LayoutInflater
+import android.view.ViewGroup
+import androidx.core.view.marginLeft
+import androidx.core.view.marginRight
+import androidx.recyclerview.widget.LinearLayoutManager
+import androidx.recyclerview.widget.RecyclerView
+import me.magnum.melonds.R
+import me.magnum.melonds.databinding.ItemRewindSaveStateBinding
+import me.magnum.melonds.ui.emulator.rewind.model.RewindSaveState
+import me.magnum.melonds.ui.emulator.rewind.model.RewindWindow
+import java.text.DecimalFormat
+import java.time.Duration
+
+class RewindSaveStateAdapter(private val onRewindSaveStateSelected: (RewindSaveState) -> Unit) : RecyclerView.Adapter<RewindSaveStateAdapter.RewindSaveStateViewHolder>() {
+
+    class RewindSaveStateViewHolder(private val context: Context, private val binding: ItemRewindSaveStateBinding) : RecyclerView.ViewHolder(binding.root) {
+
+        companion object {
+            private val SECONDS_FORMATTER = DecimalFormat("#0.##")
+        }
+
+        private lateinit var state: RewindSaveState
+
+        fun setRewindSaveState(state: RewindSaveState, window: RewindWindow) {
+            val screenshotDrawable = BitmapDrawable(context.resources, state.screenshot)
+            val durationToState = window.getDeltaFromEmulationTimeToRewindState(state)
+
+            binding.imageScreenshot.setImageDrawable(screenshotDrawable)
+            binding.textTimestamp.text = getDurationString(context, durationToState)
+            this.state = state
+        }
+
+        fun getRewindSaveState(): RewindSaveState {
+            return state
+        }
+
+        private fun getDurationString(context: Context, duration: Duration): String {
+            val minutes = duration.toMinutes()
+            return if (minutes >= 1) {
+                val seconds = duration.minusMinutes(minutes).toMillis() / 1000f
+                context.getString(R.string.rewind_time_minutes_seconds, minutes, SECONDS_FORMATTER.format(seconds))
+            } else {
+                val seconds = duration.toMillis() / 1000f
+                context.getString(R.string.rewind_time_seconds, SECONDS_FORMATTER.format(seconds))
+            }
+        }
+    }
+
+    private var currentRewindWindow: RewindWindow? = null
+    private var recyclerView: RecyclerView? = null
+
+    fun setRewindWindow(rewindWindow: RewindWindow) {
+        currentRewindWindow = rewindWindow
+        notifyDataSetChanged()
+        // Reset scroll
+        recyclerView?.scrollToPosition(0)
+    }
+
+    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): RewindSaveStateViewHolder {
+        val binding = ItemRewindSaveStateBinding.inflate(LayoutInflater.from(parent.context), parent, false)
+        val holder = RewindSaveStateViewHolder(parent.context, binding)
+        binding.root.setOnClickListener {
+            onRewindSaveStateSelected(holder.getRewindSaveState())
+        }
+        binding.root.setOnFocusChangeListener { v, hasFocus ->
+            if (hasFocus) {
+                recyclerView?.let {
+                    // Scroll to new focused item (allows controller users to properly navigate the list)
+                    val linearLayoutManager = it.layoutManager as? LinearLayoutManager ?: return@let
+                    val position = linearLayoutManager.getPosition(v)
+                    val offset = (it.width - v.width - v.marginRight - v.marginLeft) / 2
+                    linearLayoutManager.scrollToPositionWithOffset(position, offset)
+                }
+            }
+        }
+        return holder
+    }
+
+    override fun onAttachedToRecyclerView(recyclerView: RecyclerView) {
+        this.recyclerView = recyclerView
+    }
+
+    override fun onBindViewHolder(holder: RewindSaveStateViewHolder, position: Int) {
+        currentRewindWindow?.let {
+            val state = it.rewindStates[position]
+            holder.setRewindSaveState(state, it)
+        }
+    }
+
+    override fun getItemCount(): Int {
+        return currentRewindWindow?.rewindStates?.size ?: 0
+    }
+}

app/src/main/java/me/magnum/melonds/ui/emulator/rewind/model/RewindSaveState.kt

@@ -0,0 +1,13 @@
+package me.magnum.melonds.ui.emulator.rewind.model
+
+import android.graphics.Bitmap
+import me.magnum.melonds.utils.DsScreenshotConverter
+import java.nio.ByteBuffer
+
+class RewindSaveState(
+    val buffer: ByteBuffer,
+    val screenshotBuffer: ByteBuffer,
+    val frame: Int,
+) {
+    val screenshot: Bitmap get() = DsScreenshotConverter.fromByteBufferToBitmap(screenshotBuffer)
+}

app/src/main/java/me/magnum/melonds/ui/emulator/rewind/model/RewindWindow.kt

@@ -0,0 +1,20 @@
+package me.magnum.melonds.ui.emulator.rewind.model
+
+import java.time.Duration
+import java.util.*
+
+class RewindWindow(
+    val currentEmulationFrame: Int,
+    val rewindStates: ArrayList<RewindSaveState>
+) {
+
+    companion object {
+        private const val FRAMES_PER_SECOND = 60
+    }
+
+    fun getDeltaFromEmulationTimeToRewindState(state: RewindSaveState): Duration {
+        val elapsedFrames = currentEmulationFrame - state.frame
+        val elapsedMillis = elapsedFrames.toFloat() / FRAMES_PER_SECOND * 1000
+        return Duration.ofMillis(elapsedMillis.toLong())
+    }
+}

app/src/main/java/me/magnum/melonds/ui/emulator/rom/RomEmulatorDelegate.kt

@@ -27,6 +27,7 @@ class RomEmulatorDelegate(activity: EmulatorActivity, private val picasso: Picas
         SETTINGS(R.string.settings),
         SAVE_STATE(R.string.save_state),
         LOAD_STATE(R.string.load_state),
+        REWIND(R.string.rewind),
         CHEATS(R.string.cheats),
         RESET(R.string.reset),
         EXIT(R.string.exit)
@@ -142,6 +143,7 @@ class RomEmulatorDelegate(activity: EmulatorActivity, private val picasso: Picas
                 loadState(it)
                 activity.resumeEmulation()
             }
+            RomPauseMenuOptions.REWIND -> activity.openRewindWindow()
             RomPauseMenuOptions.CHEATS -> openCheatsActivity()
             RomPauseMenuOptions.RESET -> activity.resetEmulation()
             RomPauseMenuOptions.EXIT -> activity.finish()

app/src/main/java/me/magnum/melonds/utils/DsScreenshotConverter.kt

@@ -0,0 +1,24 @@
+package me.magnum.melonds.utils
+
+import android.graphics.Bitmap
+import java.nio.ByteBuffer
+
+object DsScreenshotConverter {
+    private const val SCREEN_WIDTH = 256
+    private const val SCREEN_HEIGHT = 384
+
+    fun fromByteBufferToBitmap(buffer: ByteBuffer): Bitmap {
+        return Bitmap.createBitmap(SCREEN_WIDTH, SCREEN_HEIGHT, Bitmap.Config.ARGB_8888).apply {
+            // Texture buffer is in BGR format. Convert to RGB
+            for (x in 0 until SCREEN_WIDTH) {
+                for (y in 0 until SCREEN_HEIGHT) {
+                    val b = buffer[(y * SCREEN_WIDTH + x) * 4 + 0].toInt() and 0xFF
+                    val g = buffer[(y * SCREEN_WIDTH + x) * 4 + 1].toInt() and 0xFF
+                    val r = buffer[(y * SCREEN_WIDTH + x) * 4 + 2].toInt() and 0xFF
+                    val argbPixel = 0xFF000000.toInt() or r.shl(16) or g.shl(8) or b
+                    setPixel(x, y, argbPixel)
+                }
+            }
+        }
+    }
+}

app/src/main/res/drawable/background_rewind_save_state_focused.xml

@@ -0,0 +1,9 @@
+<?xml version="1.0" encoding="utf-8"?>
+<layer-list xmlns:android="http://schemas.android.com/apk/res/android">
+    <item>
+        <shape android:shape="rectangle">
+            <solid android:color="#FFF" />
+            <corners android:radius="8dp" />
+        </shape>
+    </item>
+</layer-list>

app/src/main/res/drawable/selector_rewind_save_state.xml

@@ -0,0 +1,5 @@
+<?xml version="1.0" encoding="utf-8"?>
+<selector xmlns:android="http://schemas.android.com/apk/res/android">
+    <item android:state_focused="true" android:drawable="@drawable/background_rewind_save_state_focused" />
+    <item android:drawable="@android:color/transparent" />
+</selector>

app/src/main/res/drawable/selector_rewind_save_state_time_text.xml

@@ -0,0 +1,5 @@
+<?xml version="1.0" encoding="utf-8"?>
+<selector xmlns:android="http://schemas.android.com/apk/res/android">
+    <item android:state_focused="true" android:color="@android:color/black" />
+    <item android:color="@android:color/white" />
+</selector>

app/src/main/res/layout/activity_emulator.xml

@@ -1,40 +1,58 @@
 <?xml version="1.0" encoding="utf-8"?>
-<RelativeLayout
-    xmlns:android="http://schemas.android.com/apk/res/android"
-    xmlns:tools="http://schemas.android.com/tools"
-    android:id="@+id/layout_root"
-    android:layout_width="match_parent"
-    android:layout_height="match_parent"
-    android:background="@android:color/black"
-    tools:context=".ui.emulator.EmulatorActivity">
+<androidx.constraintlayout.motion.widget.MotionLayout
+        xmlns:android="http://schemas.android.com/apk/res/android"
+        xmlns:tools="http://schemas.android.com/tools"
+        xmlns:app="http://schemas.android.com/apk/res-auto"
+        android:id="@+id/layout_root"
+        android:layout_width="match_parent"
+        android:layout_height="match_parent"
+        android:background="@android:color/black"
+        app:layoutDescription="@xml/scene_activity_emulator"
+        tools:context=".ui.emulator.EmulatorActivity">
 
     <android.opengl.GLSurfaceView
-        android:id="@+id/surfaceMain"
-        android:layout_width="match_parent"
-        android:layout_height="match_parent"/>
+            android:id="@+id/surfaceMain"
+            android:layout_width="match_parent"
+            android:layout_height="match_parent"/>
 
     <me.magnum.melonds.ui.emulator.RuntimeLayoutView
-        android:id="@+id/view_layout_controls"
-        android:layout_width="match_parent"
-        android:layout_height="match_parent" />
+            android:id="@+id/view_layout_controls"
+            android:layout_width="match_parent"
+            android:layout_height="match_parent" />
 
     <TextView
-        android:id="@+id/textFps"
-        android:layout_width="wrap_content"
-        android:layout_height="wrap_content"
-        android:padding="12dp"
-        android:textColor="@android:color/white"
-        tools:layout_alignParentBottom="true"
-        tools:layout_centerHorizontal="true"
-        tools:text="FPS: 60"/>
+            android:id="@+id/textFps"
+            android:layout_width="wrap_content"
+            android:layout_height="wrap_content"
+            android:padding="12dp"
+            android:textColor="@android:color/white"
+            tools:text="FPS: 60"/>
 
     <TextView
-        android:id="@+id/textLoading"
-        android:layout_width="wrap_content"
-        android:layout_height="wrap_content"
-        android:layout_centerInParent="true"
-        android:textSize="32sp"
-        android:textStyle="bold"
-        android:textColor="@android:color/white"
-        android:text="@string/info_loading"/>
-</RelativeLayout>
+            android:id="@+id/textLoading"
+            android:layout_width="wrap_content"
+            android:layout_height="wrap_content"
+            android:layout_centerInParent="true"
+            app:layout_constraintStart_toStartOf="parent"
+            app:layout_constraintEnd_toEndOf="parent"
+            app:layout_constraintTop_toTopOf="parent"
+            app:layout_constraintBottom_toBottomOf="parent"
+            android:textSize="32sp"
+            android:textStyle="bold"
+            android:textColor="@android:color/white"
+            android:text="@string/info_loading"/>
+
+    <RelativeLayout
+            android:id="@+id/layout_rewind"
+            android:layout_width="match_parent"
+            android:layout_height="match_parent"
+            android:background="#A000"
+            android:focusable="false">
+    </RelativeLayout>
+
+    <androidx.recyclerview.widget.RecyclerView
+            android:id="@+id/list_rewind"
+            android:layout_width="match_parent"
+            android:layout_height="wrap_content"
+            app:layout_constraintBottom_toBottomOf="parent" />
+</androidx.constraintlayout.motion.widget.MotionLayout>

app/src/main/res/layout/item_rewind_save_state.xml

@@ -0,0 +1,31 @@
+<?xml version="1.0" encoding="utf-8"?>
+<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
+        xmlns:app="http://schemas.android.com/apk/res-auto"
+        android:layout_width="wrap_content"
+        android:layout_height="wrap_content"
+        android:layout_margin="8dp"
+        android:padding="8dp"
+        android:background="@drawable/selector_rewind_save_state"
+        android:clickable="true"
+        android:focusable="true">
+
+    <ImageView
+            android:id="@+id/image_screenshot"
+            android:layout_width="95dp"
+            android:layout_height="wrap_content"
+            app:layout_constraintStart_toStartOf="parent"
+            app:layout_constraintTop_toTopOf="parent"
+            android:contentDescription="@null"
+            android:scaleType="fitCenter"
+            android:adjustViewBounds="true" />
+
+    <TextView
+            android:id="@+id/text_timestamp"
+            android:layout_width="wrap_content"
+            android:layout_height="wrap_content"
+            android:textColor="@drawable/selector_rewind_save_state_time_text"
+            app:layout_constraintTop_toBottomOf="@id/image_screenshot"
+            app:layout_constraintStart_toStartOf="parent"
+            app:layout_constraintEnd_toEndOf="parent"
+            android:duplicateParentState="true" />
+</androidx.constraintlayout.widget.ConstraintLayout>

app/src/main/res/values/strings.xml

@@ -49,6 +49,8 @@
     <string name="cant_load_empty_slot">Can\'t load an empty save state slot</string>
     <string name="failed_reset_emulation">Failed to reset emulation</string>
     <string name="save_states_not_supported">Save states are not supported while running the firmware</string>
+    <string name="rewind_time_seconds">%1$ss</string>
+    <string name="rewind_time_minutes_seconds">%1$dm%2$ss</string>
 
     <string name="action_sort_alphabetically">Alphabetically</string>
     <string name="action_sort_recently_played">Recently played</string>
@@ -80,6 +82,7 @@
     <string name="settings">Settings</string>
     <string name="save_state">Save state</string>
     <string name="load_state">Load state</string>
+    <string name="rewind">Rewind</string>
     <string name="save_slot">Save slot</string>
     <string name="empty_slot">%1$s. &lt;Empty&gt;</string>
     <string name="quick_slot">Quick Slot</string>

app/src/main/res/xml/scene_activity_emulator.xml

@@ -0,0 +1,63 @@
+<?xml version="1.0" encoding="utf-8"?>
+<MotionScene
+        xmlns:android="http://schemas.android.com/apk/res/android"
+        xmlns:app="http://schemas.android.com/apk/res-auto">
+
+    <ConstraintSet android:id="@+id/rewind_hidden">
+        <Constraint
+                android:id="@+id/layout_rewind"
+                android:layout_width="match_parent"
+                android:layout_height="match_parent"
+                android:alpha="0"
+                android:visibility="invisible" />
+
+        <Constraint
+                android:id="@+id/list_rewind"
+                android:layout_width="match_parent"
+                android:layout_height="wrap_content"
+                app:layout_constraintTop_toBottomOf="parent"
+                android:visibility="invisible" />
+
+        <Constraint android:id="@+id/textFps">
+            <PropertySet
+                    app:applyMotionScene="false"
+                    app:visibilityMode="ignore" />
+        </Constraint>
+
+        <Constraint android:id="@+id/textLoading">
+            <PropertySet
+                    app:applyMotionScene="false"
+                    app:visibilityMode="ignore" />
+        </Constraint>
+
+        <Constraint android:id="@+id/view_layout_controls">
+            <PropertySet
+                    app:applyMotionScene="false"
+                    app:visibilityMode="ignore" />
+        </Constraint>
+    </ConstraintSet>
+
+    <ConstraintSet
+            android:id="@+id/rewind_visible"
+            app:deriveConstraintsFrom="@+id/rewind_hidden">
+
+        <Constraint
+                android:id="@id/layout_rewind"
+                android:layout_width="match_parent"
+                android:layout_height="match_parent"
+                android:alpha="1"
+                android:visibility="visible" />
+
+        <Constraint
+                android:id="@+id/list_rewind"
+                android:layout_width="match_parent"
+                android:layout_height="wrap_content"
+                app:layout_constraintBottom_toBottomOf="parent"
+                android:visibility="visible" />
+    </ConstraintSet>
+
+    <Transition
+            app:constraintSetStart="@+id/rewind_hidden"
+            app:constraintSetEnd="@id/rewind_visible"
+            app:duration="250" />
+</MotionScene>

buildSrc/src/main/kotlin/Dependencies.kt

@@ -6,6 +6,7 @@ object Dependencies {
         const val CommonsCompress = "1.21"
         const val ConstraintLayout = "2.0.4"
         const val Core = "1.6.0"
+        const val Desugar = "1.1.5"
         const val DocumentFile = "1.0.1"
         const val Flexbox = "2.0.1"
         const val Fragment = "1.3.5"
@@ -38,6 +39,10 @@ object Dependencies {
         const val kotlin = "org.jetbrains.kotlin:kotlin-gradle-plugin:${Versions.Kotlin}"
     }
 
+    object Tools {
+        const val desugarJdkLibs = "com.android.tools:desugar_jdk_libs:${Versions.Desugar}"
+    }
+
     object Kotlin {
         const val kotlinStdlib = "org.jetbrains.kotlin:kotlin-stdlib-jdk7:${Versions.Kotlin}"
     }

melonDS-android-lib

@@ -1 +1 @@
-Subproject commit bb35140d03af0034f7f759bcb497289d7e7603c5
+Subproject commit 159c113545484fc38c0d74c7f8d066a626093911