How do I convert a UIImage to a coil image

[AlexanderEggers]

I have a use-case in my app where I need to convert a UIImage to a coil image. I'm trying to build a custom convert for using blurhash in my project. Coil doesn't seem to support this at the moment.

[colinrtwhite]

I don't think this is possible - Images need to be able to render to a Skia canvas, which I'm not sure an iOS UIImage can.

[kihaki]

You can convert an UIImage to a ByteArray, peekaboo does this

@OptIn(ExperimentalForeignApi::class)
private fun UIImage.toByteArray(compressionQuality: Double): ByteArray {
    val validCompressionQuality = compressionQuality.coerceIn(0.0, 1.0)
    val jpegData = UIImageJPEGRepresentation(this, validCompressionQuality)!!
    return ByteArray(jpegData.length.toInt()).apply {
        memcpy(this.refTo(0), jpegData.bytes, jpegData.length)
    }
}

The ByteArray can then probably be converted into a Bitmap which then can be used in a coil Image.

I am currently on the second step (ByteArray -> Bitmap), will post again once I got it working..

Di you already make it work @AlexanderEggers ?

[kihaki]

I have managed to use the above code to create an Buffer that contains the UIImages content as Jpeg ByteArray

val jpegByteArray = uiImage.toByteArray(80.0)
val buffer = Buffer()
buffer.write(jpegByteArray)

This probably copies the whole ByteArray without any gain, but I have so far not found a zero-copy method of turning a ByteArray into a Buffer - if someone has something like that, that would be great.

The result can then be passed to a coil SourceFetchResult

SourceFetchResult(
  source = ImageSource(buffer, FileSystem.SYSTEM),
  mimeType = "image/jpeg",
  dataSource = DataSource.MEMORY
)

which then can be used inside of a custom Fetcher.

This works for picking an image from the iOS PhotoPicker and display that image in a LazyColumn in Compose Multiplatform with Coil. Performance so far is great on the emulator, though to be fair, the emulator runs on an M1, which might just be so powerful as not to notice any performance problems.. haven't tested it on a real iOS device yet.