Demo animated content scale

demos/compose/src/main/java/androidx/media3/demo/compose/MainActivity.kt

@@ -21,6 +21,9 @@ import android.os.Bundle
 import androidx.activity.ComponentActivity
 import androidx.activity.compose.setContent
 import androidx.activity.enableEdgeToEdge
+import androidx.compose.animation.core.Spring
+import androidx.compose.animation.core.animate
+import androidx.compose.animation.core.spring
 import androidx.compose.foundation.background
 import androidx.compose.foundation.layout.Box
 import androidx.compose.foundation.layout.fillMaxSize
@@ -30,15 +33,20 @@ import androidx.compose.foundation.layout.padding
 import androidx.compose.material3.Button
 import androidx.compose.material3.Text
 import androidx.compose.runtime.Composable
+import androidx.compose.runtime.LaunchedEffect
 import androidx.compose.runtime.getValue
+import androidx.compose.runtime.mutableFloatStateOf
 import androidx.compose.runtime.mutableIntStateOf
 import androidx.compose.runtime.mutableStateOf
 import androidx.compose.runtime.remember
 import androidx.compose.runtime.setValue
 import androidx.compose.ui.Alignment
 import androidx.compose.ui.Modifier
+import androidx.compose.ui.geometry.Size
 import androidx.compose.ui.graphics.Color
 import androidx.compose.ui.layout.ContentScale
+import androidx.compose.ui.layout.ScaleFactor
+import androidx.compose.ui.layout.lerp
 import androidx.compose.ui.platform.LocalContext
 import androidx.compose.ui.unit.dp
 import androidx.lifecycle.compose.LifecycleResumeEffect
@@ -124,7 +132,7 @@ private fun MediaPlayerScreen(player: Player, modifier: Modifier = Modifier) {
       player = player,
       surfaceType = SURFACE_TYPE_SURFACE_VIEW,
       modifier = Modifier.noRippleClickable { showControls = !showControls },
-      contentScale = contentScales[currentContentScaleIndex].second
+      contentScale = contentScales[currentContentScaleIndex].second.interpolate()
     )
     if (!renderingState.renderedFirstFrame) {
       // hide the surface that is being prepared behind a scrim
@@ -147,3 +155,87 @@ private fun MediaPlayerScreen(player: Player, modifier: Modifier = Modifier) {
     }
   }
 }
+
+
+
+@Composable
+private fun ContentScale.interpolate(): ContentScale {
+  var interpolation by remember {
+    mutableFloatStateOf(1f)
+  }
+  var previousScale by remember {
+    mutableStateOf(this)
+  }
+  val currentScale by remember {
+    mutableStateOf(this)
+  }.apply {
+    if (value != this@interpolate) previousScale = when {
+      interpolation == 1f -> value
+      else -> CapturedContentScale(
+        capturedInterpolation = interpolation,
+        previousScale = previousScale,
+        currentScale = value
+      )
+    }.also { interpolation = 0f }
+    value = this@interpolate
+  }
+
+  LaunchedEffect(currentScale) {
+    animate(
+      initialValue = 0f,
+      targetValue = 1f,
+      animationSpec = spring(
+        stiffness = Spring.StiffnessMedium
+      ),
+      block = { progress, _ ->
+        interpolation = progress
+      },
+    )
+  }
+
+  return remember {
+    object : ContentScale {
+      override fun computeScaleFactor(
+        srcSize: Size,
+        dstSize: Size
+      ): ScaleFactor {
+        val start = previousScale.computeScaleFactor(
+          srcSize = srcSize,
+          dstSize = dstSize
+        )
+        val stop = currentScale.computeScaleFactor(
+          srcSize = srcSize,
+          dstSize = dstSize
+        )
+        return if (start == stop) stop
+        else lerp(
+          start = start,
+          stop = stop,
+          fraction = interpolation
+        )
+      }
+    }
+  }
+}
+
+private class CapturedContentScale(
+  private val capturedInterpolation: Float,
+  private val previousScale: ContentScale,
+  private val currentScale: ContentScale,
+) : ContentScale {
+
+  override fun computeScaleFactor(
+    srcSize: Size,
+    dstSize: Size
+  ): ScaleFactor = lerp(
+    start = previousScale.computeScaleFactor(
+      srcSize = srcSize,
+      dstSize = dstSize
+    ),
+    stop = currentScale.computeScaleFactor(
+      srcSize = srcSize,
+      dstSize = dstSize
+    ),
+    fraction = capturedInterpolation
+  )
+}