Add support for WEBP or PNG with transparency to Tiles image helpers

[yschimke]

The current conversion code for bitmaps and canvas elements to Tile ImageResources, uses RGB_565.

horologist/tiles/src/main/java/com/google/android/horologist/tiles/images/images.kt

Line 69 in 40801e6

public fun Bitmap.toImageResource(): ImageResource {

This is safe format, but requires extra work and also does not support alpha channel.

We should add a flag to support other formats including png, webp.

This probably involves removing hard coded format when flag is set

setFormat(ResourceBuilders.IMAGE_FORMAT_RGB_565)

and use, or other conversion code.

    val bytes = ByteArrayOutputStream().apply {
        compress(Bitmap.CompressFormat.PNG, 100, this)
    }.toByteArray()

We can assume Coil for our conversion code if it helps, and to start with avoiding conversions, but to be confirmed.

A later change might be also this code path https://github.com/google/horologist/blob/2f15272f92291bcdbdacd66b1042e42802c45cb7/tiles/src/main/java/com/google/android/horologist/tiles/canvas/canvas.kt

[yschimke]

cc @ataulm

[yschimke]

We should make this a flag, useRgb565?

Current logic when useRgb565.

When not useRgb565, remove setFormat, and pass through the existing bytes. Tile rendering should ask the system to decode.

Samples should show a png, webp or jpg working without conversion.

[ataulm]

I think for a "good first issue" this needs more context:

• what's the problem and which APIs does this affect currently?
• Are we talking only about this function? Or will further changes need to be made elsewhere?
• is this something that we can do without exposing a flag/new API? e.g. detect the type of the image and convert it with the correct compression?
• are there similar APIs in well-established libraries like Coil, Glide and Picasso that we should follow?