Sub-sampling

For displaying large images that may not fit into memory, ZoomableImage automatically divides them into tiles so that they can be loaded lazily.

If ZoomableImage can't be used or if sub-sampling of images is always desired, you could potentially use SubSamplingImage() directly.

implementation("me.saket.telephoto:sub-sampling-image:0.15.1")

val zoomableState = rememberZoomableState()
val imageState = rememberSubSamplingImageState(
  zoomableState = zoomableState,
  imageSource = SubSamplingImageSource.asset("fox.jpg")
)

SubSamplingImage(
  modifier = Modifier
    .fillMaxSize()
    .zoomable(zoomableState),
  state = imageState,
  contentDescription = …,
)

SubSamplingImage() is an adaptation of the excellent subsampling-scale-image-view by Dave Morrissey.

Custom image sources

SubSamplingImage() isn't limited to simple images. It can also be used to display custom content, such as PDFs or small maps, by using custom implementations of SubSamplingImageSource:

val imageSource = FooImageSource(…)
val zoomableState = rememberZoomableState()

SubSamplingImage(
  modifier = Modifier
    .fillMaxSize()
    .zoomable(zoomableState),
  state = rememberSubSamplingImageState(imageSource, zoomableState),
  contentDescription = …,
)

class FooImageSource(
  override val preview: ImageBitmap?
) : SubSamplingImageSource {

  override suspend fun decoder(): ImageRegionDecoder.Factory {
    return ImageRegionDecoder.Factory { params ->
      TODO("Create an image decoder that can load images for your content")
    }
  }
}

Custom SubSamplingImageSource values can also be used with Zoomable*Image() via a custom image loader.