Reproducer for: Coil does not apply contentScale to placeholder/error

composeApp/src/androidMain/kotlin/app/playground/android/BlurHashPainter.kt

@@ -0,0 +1,113 @@
+package app.playground
+
+import androidx.compose.runtime.Composable
+import androidx.compose.runtime.RememberObserver
+import androidx.compose.runtime.getValue
+import androidx.compose.runtime.mutableStateOf
+import androidx.compose.runtime.remember
+import androidx.compose.runtime.setValue
+import androidx.compose.ui.geometry.Size
+import androidx.compose.ui.graphics.Color
+import androidx.compose.ui.graphics.ColorFilter
+import androidx.compose.ui.graphics.DefaultAlpha
+import androidx.compose.ui.graphics.asImageBitmap
+import androidx.compose.ui.graphics.drawscope.DrawScope
+import androidx.compose.ui.graphics.painter.BitmapPainter
+import androidx.compose.ui.graphics.painter.ColorPainter
+import androidx.compose.ui.graphics.painter.Painter
+import androidx.compose.ui.platform.LocalDensity
+import androidx.compose.ui.platform.LocalInspectionMode
+import androidx.compose.ui.unit.Density
+import androidx.compose.ui.unit.dp
+import app.playground.BlurHashModel
+import com.vanniktech.blurhash.BlurHash
+import kotlinx.coroutines.CoroutineScope
+import kotlinx.coroutines.Dispatchers
+import kotlinx.coroutines.cancel
+import kotlinx.coroutines.launch
+import kotlinx.coroutines.withContext
+import kotlin.math.roundToInt
+
+@Composable
+actual fun rememberBlurHashPainter(blurHash: BlurHashModel): Painter {
+  // todo: can i read the density from DrawScope instead?
+  val density = LocalDensity.current
+  val isInPreview = LocalInspectionMode.current
+  return remember(blurHash, density) {
+    AsyncBlurHashPainter(blurHash, density, isInPreview)
+  }
+}
+
+private class AsyncBlurHashPainter(
+  private val blurHash: BlurHashModel,
+  private val density: Density,
+  private val isInPreview: Boolean,
+) : Painter(),
+  RememberObserver {
+
+  private var painter: Painter? by mutableStateOf(null)
+  private var scope: CoroutineScope? = null
+  private var alpha: Float = DefaultAlpha
+  private var colorFilter: ColorFilter? = null
+
+  override val intrinsicSize: Size
+    get() = painter?.intrinsicSize ?: Size.Unspecified
+
+  override fun onRemembered() {
+    if (isInPreview) {
+      painter = blurHash.createPainter(density)
+    } else {
+      scope = CoroutineScope(Dispatchers.Main.immediate).apply {
+        launch {
+          painter = withContext(Dispatchers.IO) {
+            blurHash.createPainter(density)
+          }
+        }
+      }
+    }
+  }
+
+  override fun onForgotten() {
+    scope?.cancel()
+  }
+
+  override fun onAbandoned() = Unit
+
+  override fun applyAlpha(alpha: Float): Boolean {
+    this.alpha = alpha
+    return true
+  }
+
+  override fun applyColorFilter(colorFilter: ColorFilter?): Boolean {
+    this.colorFilter = colorFilter
+    return true
+  }
+
+  override fun DrawScope.onDraw() {
+    painter?.let { painter ->
+      with(painter) {
+        draw(size, alpha, colorFilter)
+      }
+    }
+  }
+
+  private fun BlurHashModel.createPainter(density: Density): Painter {
+    check(width > 0 && height > 0)
+
+    // Smaller bitmaps are significantly cheaper to generate with little reduction in blur quality.
+    val maxWidthPx = density.run { 80.dp.roundToPx() }
+    val aspectRatio = width.toFloat() / height
+    val constrainedWidth = (width / 4).coerceAtMost(maxWidthPx)
+
+    val bitmap = BlurHash.decode(
+      blurHash = hash,
+      width = constrainedWidth,
+      height = (constrainedWidth / aspectRatio).roundToInt(),
+    )
+
+    return when (bitmap) {
+      null -> ColorPainter(Color.Transparent)
+      else -> BitmapPainter(bitmap.asImageBitmap())
+    }
+  }
+}

composeApp/src/commonMain/kotlin/app/playground/BlurHashPainter.kt

@@ -0,0 +1,13 @@
+package app.playground
+
+import androidx.compose.runtime.Composable
+import androidx.compose.ui.graphics.painter.Painter
+
+data class BlurHashModel(
+  val hash: String,
+  val width: Int,
+  val height: Int,
+)
+
+@Composable
+expect fun rememberBlurHashPainter(blurHash: BlurHashModel): Painter

composeApp/src/commonMain/kotlin/app/playground/MainScreen.kt

@@ -1,12 +1,50 @@
 package app.playground
 
 import androidx.compose.foundation.layout.Column
+import androidx.compose.foundation.layout.aspectRatio
+import androidx.compose.foundation.layout.fillMaxWidth
 import androidx.compose.material3.Text
 import androidx.compose.runtime.Composable
+import androidx.compose.runtime.RememberObserver
+import androidx.compose.runtime.getValue
+import androidx.compose.runtime.mutableStateOf
+import androidx.compose.runtime.setValue
+import androidx.compose.ui.Modifier
+import androidx.compose.ui.geometry.Size
+import androidx.compose.ui.graphics.ColorFilter
+import androidx.compose.ui.graphics.DefaultAlpha
+import androidx.compose.ui.graphics.drawscope.DrawScope
+import androidx.compose.ui.graphics.painter.Painter
+import androidx.compose.ui.layout.ContentScale
+import androidx.compose.ui.unit.Density
 import androidx.navigation.NavHostController
+import coil3.compose.AsyncImage
+import kotlinx.coroutines.CoroutineScope
+import kotlinx.coroutines.Dispatchers
+import kotlinx.coroutines.cancel
+import kotlinx.coroutines.launch
+import kotlinx.coroutines.withContext
+import kotlin.math.roundToInt
 
 @Composable internal fun MainScreen(
   navHostController: NavHostController,
 ) = Column {
   Text("Hello World")
+
+  val placeholder = rememberBlurHashPainter(
+    BlurHashModel(
+      hash = "LEHLk~WB2yk8pyo0adR*.7kCMdnj",
+      width = 100,
+      height = 100,
+    ),
+  )
+
+  AsyncImage(
+    model = "https://www.google.com/url?sa=i&url=https%3A%2F%2Fcommons.wikimedia.org%2Fwiki%2FFile%3ATest.svg&psig=AOvVaw0YE5gD2JedL-Twca2x2_us&ust=1732595398709000&source=images&cd=vfe&opi=89978449&ved=0CBEQjRxqFwoTCKiigv7S9okDFQAAAAAdAAAAABAE",
+    contentScale = ContentScale.Fit,
+    contentDescription = null,
+    placeholder = placeholder,
+    error = placeholder,
+    modifier = Modifier.fillMaxWidth(fraction = 1f).aspectRatio(1f),
+  )
 }