Are there APIs for image convolutions in Compose (...

# compose

[Kirill Grouchnikov]

Are there APIs for image convolutions in Compose (on ImageBitmap)? In general, there doesn't seem to be a way, maybe by design, to get access to the underlying pixel information for direct manipulation. AndroidImageAsset and DesktopImageAsset go through a somewhat of a contortion to expose the underlying pixel information to the ImageBitmap, but I don't see any way to get those pixels afterwards.

[cb]

There's the new toPixelMap() which gives you read access to the pixels. You say manipulation, as in to mutate the pixel array values?

[Kirill Grouchnikov]

Yes. This is common for libraries that provide dynamically generated image effects where you don't necessarily have an asset to begin with. One use case is to dynamically generate a texture (noise, weave, fabric, anything really), then apply a set of filters / convolutions directly to the int array, and then create an ImageBitmap out of the final buffer.

[Kirill Grouchnikov]

And image convolution is a common thing as well. On Android it can be done with RenderScript (see https://blog.stylingandroid.com/image-convolution-implementation/) but that wouldn't translate directly to Compose. In general, it's about dropping down to the underlying buffer of pixels for reading, transforming and creating a new buffer, and then creating a new image out of it. Or alternatively, rewriting the pixels in the destination so that you don't create a new image object every time.

[Nader Jawad]

Right now there is no support for image convolutions in compose. Nowadays if folks want to manipulate textures they usually leverage opengl. But as @cb mentioned if you want to query pixel formation you can use the toPixelMap api on ImageBitmap or provide your own array to store pixel information using readPixels

[Kirill Grouchnikov]

Is it only on ImageAsset or also on ImageBitmap?

[Nader Jawad]

ImageAsset is renamed to ImageBitmap

[Nader Jawad]

And there is a type alias for ImageAsset that points to ImageBitmap

[Nader Jawad]

toPixelMap is an extension method on ImageBitmap which would need an explicit import.

[Kirill Grouchnikov]

Ah great, I missed the alias part. So I can use readPixels for two things. Get pixels from an existing image, and also do that same "remapping" trick as in AndroidImageAsset and DesktopImageAsset to map a dynamically created buffer of pixels to a compose image object that can be drawn on a canvas.

[Kirill Grouchnikov]

Well, that didn't work - see my latest post in this channel. I can create a custom implementation of ImageAsset, and then it's going to throw an UnsupportedOperationException while drawing it on a canvas