Expose an API for converting DrawableResource -> ByteArray

[colinrtwhite]

Hi I'm looking to add support for the new multiplatform resources API in Coil so it's possible to do:

AsyncImage(
  model = Res.drawable.image,
  contentDescription = null,
)

Using AsyncImage would have a couple benefits vs. using Image and painterResource:

• Automatic downscaling for large images into small layout bounds.
• Support for Decoders to decode custom file types.
• More memory cache control (e.g. control size and use LRU eviction, or disable caching).
• AsyncImage is a unified API that supports the file system and network URLs too.

At the moment I don't think it's possible to add support as the APIs to fetch a resource (readResourceBytes, Resource.getPathByEnvironment, and ResourceEnvironment) are internal. Res.readBytes is public, but it's generated so it can't easily be used in libraries. Res.readBytes also requires a path, but there's no public method to convert a DrawableResource into a path.

I think exposing LocalComposeEnvironment.current.rememberEnvironment() and resource.getPathByEnvironment(environment) (basically whatever painterResource(resource: DrawableResource) uses) would be enough to support this, but let me know what you think!

[dima-avdeev-jb]

Thanks! We will discuss it.

[terrakok]

Hi @colinrtwhite ! I have an idea to add a function getAsUri(Res id). It will return an uri to the file based on current environment. Does it cover your case?

[colinrtwhite]

@terrakok Yep, I think that would work! Thinking out loud this is how Coil would use it:

• The user passes DrawableResource to AsyncImage.
• AsyncImage uses getAsUri to translate the DrawableResource -> String (or URI type)
• The URI is passed to the ImageLoader, which can already handle most URI formats (network, disk, Android R, etc.)

[terrakok]

Hi @colinrtwhite! I returned to the issue and think there is a problem: when we try to convert a DrawableResource to the Uri string, we do this depending on a current environment. It is a hidden logic which can leak to user's code. The uri string is static and points on concrete file instead of a dynamic accessor with the environment handling.

fun DrawableResource.toUri(): String {
    val resource = this
    val resourceReader = LocalResourceReader.current
    val environment = LocalComposeEnvironment.current.rememberEnvironment()
    val resourceItem = remember(resource, environment) { resource.getResourceItemByEnvironment(environment) }
    return resourceReader.getUri(resourceItem.path)
}

So, I will add the uri getter only for files by path: Res.getUri("files/map.png"). I hope it is enough. All coil's features will work for resources and the resource library API won't be broken.

[colinrtwhite]

@terrakok Thanks for the update. Unfortunately, I don't think this solves the use case as Res is a generated class that Coil, as a library, can't directly reference so we can't call Res.getUri. The underlying method getResourceUri is marked as an internal API so we can't use that either.

Also it sounds like it won't be possible to load the generated DrawableResource entries? I was hoping to be able to support DrawableResource references as I think most users will prefer type safe drawable references vs. string paths. Is it possible to expose the path associated with a DrawableResource? Then that path could be used to get the URI, which can then be loaded by Coil.

[terrakok]

I don't say the coil calls Res.getUri. I'd expect a user may pass an uri string to the coil. Will it work?

AsyncImage(
  model = Res.getUri("files/my_photo.jpg"),
  contentDescription = null,
)

Regarding type safe drawable references, could you explain why the following approach doesn't work for you?

AsyncImage(
  model = painterResource(Res.drawable.some_icon),
  contentDescription = null,
)

[colinrtwhite]

@terrakok Ah sorry - passing model = Res.getUri("files/my_photo.jpg") would work! That API does make it possible to load images given their path. Will it also work for images in the drawable folder: Res.getUri("drawable/my_photo.jpg")?

For model = painterResource(Res.drawable.some_icon) we could support it, but then there isn't any benefit to using AsyncImage over Image. The image is decoded by painterResource so AsyncImage wouldn't be able to downscale the image into the composable's bounds or add support for custom decoders.