coil-compose

Coil 3 for Compose & Compose Multiplatform

This reference covers the KMP specifics and two performance guardrails, not the basics of AsyncImage / SubcomposeAsyncImage / ImageRequest / placeholder / error / contentDescription / a shared ImageLoader.

KMP: LocalPlatformContext, not LocalContext

Coil 3 is fully multiplatform — AsyncImage / SubcomposeAsyncImage / rememberAsyncImagePainter are identical in commonMain, with no expect/actual needed. The one swap: use LocalPlatformContext.current, not LocalContext.current (Android-only; a compile error in commonMain). It resolves to android.content.Context on Android and PlatformContext.INSTANCE on other targets.

// commonMain — works on all platforms
AsyncImage(
    model = ImageRequest.Builder(LocalPlatformContext.current).data(url).crossfade(true).build(),
    contentDescription = "User avatar",
    modifier = Modifier.size(48.dp).clip(CircleShape),
)

Singleton setup (KMP): call SingletonImageLoader.setSafe { ImageLoader.Builder(it).crossfade(true).build() } once early in the app lifecycle, or pass an imageLoader explicitly. coil-compose vs coil-compose-core: with coil-compose, AsyncImage without an imageLoader argument uses the singleton automatically; with coil-compose-core, the imageLoader parameter is required (no singleton convenience). Add a platform network engine as needed (e.g. coil-network-ktor3 for KMP).

Two performance guardrails

SubcomposeAsyncImage is significantly slower than regular composition — never use it inside LazyColumn / LazyRow. It creates a subcomposition per item; during scroll that overhead accumulates into visible jank. For custom loading/error states in a list, use AsyncImage with placeholder / error parameters instead — same visual result, no subcomposition.

rememberAsyncImagePainter does NOT infer the display size from layout constraints — without an explicit .size() it loads the image at its original dimensions (a 4000×3000 photo shown at 64dp still occupies the full bitmap in memory → OOM in a 50-item list). Reach for it only when a Painter is strictly required (Canvas, Icon, a custom draw); always pass .size(). Otherwise use AsyncImage, which sizes automatically.

// only when a Painter is genuinely required — explicit size is mandatory
val painter = rememberAsyncImagePainter(
    ImageRequest.Builder(LocalPlatformContext.current).data(url).size(Size(128, 128)).build(),
)
Image(painter = painter, contentDescription = null)