feat(desktop): expose whether the first frame has been rendered

mediaplayer/src/commonMain/kotlin/io/github/kdroidfilter/composemediaplayer/VideoPlayerState.kt

@@ -87,6 +87,14 @@ interface VideoPlayerState {
     var isFullscreen: Boolean
     val aspectRatio: Float
 
+    /**
+     * Whether a frame of the current media has been handed to the surface. False until the first frame after
+     * [openUri] / [openFile], so a caller can keep a placeholder or loader up until there is a picture to show.
+     *
+     * Reported by the desktop (JVM) players; false on the other platforms for now.
+     */
+    val hasRenderedFirstFrame: Boolean get() = false
+
     val isPipSupported: Boolean get() = false
     var isPipActive: Boolean get() = false
         set(value) {}

mediaplayer/src/jvmMain/kotlin/io/github/kdroidfilter/composemediaplayer/VideoPlayerState.jvm.kt

@@ -84,6 +84,7 @@ open class DefaultVideoPlayerState : VideoPlayerState {
 
     override val metadata: VideoMetadata get() = delegate.metadata
     override val aspectRatio: Float get() = delegate.aspectRatio
+    override val hasRenderedFirstFrame: Boolean get() = delegate.hasRenderedFirstFrame
 
     override var subtitlesEnabled = delegate.subtitlesEnabled
     override var currentSubtitleTrack: SubtitleTrack? = delegate.currentSubtitleTrack

mediaplayer/src/jvmMain/kotlin/io/github/kdroidfilter/composemediaplayer/linux/LinuxVideoPlayerState.kt

@@ -47,6 +47,10 @@ class LinuxVideoPlayerState : VideoPlayerState {
     private val _currentFrameState = MutableStateFlow<ImageBitmap?>(null)
     internal val currentFrameState: State<ImageBitmap?> = mutableStateOf(null)
 
+    // The last frame stays on the surface across an open, so the first frame of a media is tracked on its own
+    private var _hasRenderedFirstFrame by mutableStateOf(false)
+    override val hasRenderedFirstFrame: Boolean get() = _hasRenderedFirstFrame
+
     // Double-buffered Skia bitmaps
     private var skiaBitmapWidth: Int = 0
     private var skiaBitmapHeight: Int = 0
@@ -174,6 +178,7 @@ class LinuxVideoPlayerState : VideoPlayerState {
                     ensureActive()
                     withContext(Dispatchers.Main) {
                         (currentFrameState as MutableState).value = newFrame
+                    if (newFrame != null) _hasRenderedFirstFrame = true
                     }
                 }
             }
@@ -235,6 +240,7 @@ class LinuxVideoPlayerState : VideoPlayerState {
                 isLoading = true
                 error = null
                 playbackSpeed = 1.0f
+                _hasRenderedFirstFrame = false
             }
 
             try {

mediaplayer/src/jvmMain/kotlin/io/github/kdroidfilter/composemediaplayer/mac/MacVideoPlayerState.kt

@@ -183,6 +183,9 @@ class MacVideoPlayerState : VideoPlayerState {
     private val bitmapLock = ReentrantReadWriteLock()
     internal val currentFrameState = mutableStateOf<ImageBitmap?>(null)
 
+    // currentFrameState is cleared on every open (releaseAllResources) and set by the first consumed frame
+    override val hasRenderedFirstFrame: Boolean get() = currentFrameState.value != null
+
     // Aspect ratio — driven by the live frame (see syncAspectRatioToFrame).
     private var _aspectRatio by mutableStateOf(16f / 9f)
     override val aspectRatio: Float get() = _aspectRatio

mediaplayer/src/jvmMain/kotlin/io/github/kdroidfilter/composemediaplayer/windows/WindowsVideoPlayerState.kt

@@ -207,6 +207,9 @@ class WindowsVideoPlayerState : VideoPlayerState {
     private val bitmapLock = ReentrantReadWriteLock()
     internal val currentFrameState = mutableStateOf<ImageBitmap?>(null)
 
+    // currentFrameState is cleared on every open (releaseAllResources) and set by the first consumed frame
+    override val hasRenderedFirstFrame: Boolean get() = currentFrameState.value != null
+
     // Aspect ratio property
     override val aspectRatio: Float
         get() =