Hi I m curious about design decisions between Compose and Sc

Question

Hi I m curious about design decisions between Compose and Scala Binding <https github com ThoughtWorksInc Binding scala design> and why Compose wasn t designed towards Scala Binding but went to kind of virtual DOM way

gildor · Answer

There is no any kind virtual DOM in Compose

gildor · Answer

You can check implementation details in article <http intelligiblebabble com compose from first principles >

Antanas A. · Answer

so when it feels like mechanism is the same as scala binding

Antanas A. · Answer

``` Unlike ReactJS a Binding scala dom method is NOT a regular function It is a template that describes the relationship between data source and the DOM When part of the data source changes Binding scala knows about the exact corresponding partial DOM affected by the change thus only re evaluating that part of the dom method to reflect the change in the DOM ```

Antanas A. · Answer

So the Compose is some kind of reactive model to AST tree transformer

Antanas A. · Answer

but does it emit transformation instructions of AST

Antanas A. · Answer

or how exactly GUI rendering pipeline knows what to rerender

Antanas A. · Answer

or these lightweight Composable functions nodes is bound to some kind of lambda callback functions factory and or update which gets called when needed

karelpeeters · Answer

See the blog post a couple of comments up <http intelligiblebabble com compose from first principles > for some details of the inner workings

Leland Richardson [G] · Answer

< Antanas A > if you re asking how compose can know how to recompose just part of the composition hierarchy you re right that i did not attempt to cover that in the article slightly smiling face It was getting long as is and didn t want to throw another wrench into it Compose works similar to how you suggest There are parts of the tree we call recompose scopes which can be thought of as parameterless lambdas and a starting position of the backing memoization cache which we call SlotTable With this information you can start at a point in the middle of the tree

Chuck Jazdzewski [G] · Answer

An ` Composable` function is transform function from its parameters to a mutable tree In Compose the tree represents the UI of an application The tree is responsible for tracking when it is modified as a result of composition to track when and where the screen should be updated

Antanas A. · Answer

thanks for responses

Antanas A. · Answer

but how exactly rendering engine binds to that tree Are there some observables which can be listened to Or it returns a stream of changes Im trying to imagine how different graphic engines will consume that tree

Ryan Mentley · Answer

If you re interested in how drawing is currently implemented it s here <https android googlesource com platform frameworks support + f2ee53da301a9527cf426cbb47c1d4b9c4cc76fc ui platform src main java androidx ui core AndroidOwner kt 256>

Ryan Mentley · Answer

Basically it walks down the tree and calls the draw nodes