Make coil-gif multiplatform

[outadoc]

This PR intends to bring animated GIF support to iOS and other non-Android platforms. (see #2347)

A new AnimatedSkiaImageDecoder has been integrated in nonAndroidMain, largely based on @colinrtwhite's POC, with added support for looping GIFs.

Since Skia natively supports animated WebP, this new decoder also supports them. I've validated that with a test image in the sample app, but I haven't committed it. I'm not sure if other formats (HEIF?) could be supported; I couldn't find proper images to test, so for now the decoder won't try to decode them.

• The coil-gif artifact has been converted to Kotlin Multiplatform
• decodeUtils.kt has been moved to commonMain, while the rest of the code stays in androidMain
• apiDump has been run
• Tests have been run
• The documentation has been updated
• The changes have been tested on Android, iOS and Desktop in the sample app
• Buffer next frames in the background
• Support AnimatedTransformation in AnimatedSkiaImage and update docs
• Support extra options in AnimatedSkiaImage
• Write new Skia tests

iOS preview

ios.mp4

Desktop preview

Enregistrement.de.l.ecran.2024-10-26.a.17.11.45.mov

[outadoc]

@colinrtwhite Hi! Feel entirely free to make suggestions or even entirely take over the PR if you feel like it. As you can see, it's based on your POC, so it should be familiar. I'm a graphics newbie, so there's probably a lot to improve still -- but hopefully this helps the project 😄

[colinrtwhite]

Thanks! Added some comments that we'll need to tackle before merging. I can take those on after the Coil 3.1 release or feel free to take a stab at the changes if you'd like. We'll also need to add tests for this before we can merge it.

[colinrtwhite]

We should introduce a common function like AnimatedImageDecoderFactory (not sure about the naming) that automatically returns the right decoder factory implementation for the platform/API level. That way we could recommend:

val imageLoader = ImageLoader.Builder(context)
    .components {
        add(AnimatedImageDecoderFactory())
    }
    .build()

in the readme.

[colinrtwhite]

I think we can support this on all platforms by replacing android.graphics.Canvas with coil3.Canvas in AnimatedTransformation.

[colinrtwhite]

We'll need to pass through Options so we can add support for all the properties in coil3/gif/imageRequest.kt. I don't think we should ship this without adding support for those properties first.

[colinrtwhite]

I think we'll need to tweak this to something like bufferedFramesCount (pass 0 for disabled, Int.MAX_VALUE to buffer everything) since we'll need to update the implementation to buffer a few frames up front then buffer the rest just in time before we need to draw them.

We'll want to buffer X frames during the decode process then figure out how to get a CoroutineScope so we can decode the rest right after AnimatedSkiaImage.draw is called.

[outadoc]

@colinrtwhite Thank you for your feedback. I'll try to address it as much as I can 🙂

[outadoc]

I've written JVM tests and rewritten some of the code to fix issues. I'm pretty satisfied with how the PR is turning out, even if we could still add more tests, I'm sure.

[revonateB0T]

Is there any possibility to use natively allocated pixels buffer?
Although desktop jvm has larger heap size, I don't think store pixels in jvm heap is a good idea.
Moreover, buffer size is not changed, we could just use two or three buffer to do something like decode-render-swap, just like vulkan swapchain, this help us avoid allocating extra memory.