How to support touchscreen?

[Richyeoh]

I have a window pad，I running app on that，App is very simple just a LazyColumn，It can use mouse wheel scroll，but not use touchscreen scroll.

[Richyeoh]

I see Modifier extensions function has a mouseScroll and mouseTouch，How to use it ? Thx~

[Richyeoh]

Hi @akurasov, Do you know how to solve this problem? I saw that you mentioned relevant problems and tried, but I still can't solve the problem of dragging and scrolling on the touch screen.

[Richyeoh]

val scrollState = rememberLazyListState()
val data = (0 until 1000).map { "Item $it" }
LazyColumn(
    modifier = Modifier.draggable(rememberDraggableState { delta ->
        println("delta=$delta")
        runBlocking {
            scrollState.scrollBy(-delta)
        }
    }, orientation = Orientation.Vertical),
    state = scrollState
) {
    items(data) { i ->
        Text(
            i,
            Modifier
                .padding(14.dp)
                .fillMaxWidth()
        )
    }
}

See above code:
Maybe, I has solve the problem.

[akurasov]

Yes, if you want to handle dragging gesture, you should use this API.

There is no explicit touch screen support, Compose relies on OS level conversion of touch Screen events to mouse events.

[hasali19]

Is there a plan to implement proper touch screen support? I actually attempted to pass through touch events while trying out compose, using the ComposeScene, but found that certain components such as TextField are hard coded to only work properly for mouse input on desktop.

[akurasov]

There are no immediate plans for it. Could you please describe some scenarios, where current support is not enough?

[hasali19]

There's no fling behaviour when scrolling with the above method, and no way to differentiate between mouse and touch gestures.

[ianbrandt]

There are no immediate plans for it. Could you please describe some scenarios, where current support is not enough?

My use case is a GUI client that includes 2D and 3D mapping functionality. It can be run on any Windows or Linux multitouch-enabled device. Examples include laptops and desktops with monitors having multitouch support, Microsoft Surface and Linux tablet devices, and similar. For 2D maps (think Google Maps) it supports simultaneous pinch-to-zoom, drag-to-pan, and twist-to-rotate two-finger gestures. For 3D maps (think Google Earth) it's the same, with the addition that switching to three-fingered gestures changes drag-to-pan to drag-to-pan-horizontally-and-tilt-vertically. The client can sometimes be used in high-criticality (i.e. potential loss of life) situations, so precise, performant touch and gesture control is vital.

Currently we use OpenJFX for this, in particular its TouchEvent and GestureEvent multitouch support. See also "Handling JavaFX Events: Working with Events from Touch-Enabled Devices" and "Handling JavaFX Events: Working with Touch Events".

I'd like to consider porting to Compose Multiplatform in the future to support Windows and Linux desktop, Android, and WASM targets all from a single client, but multitouch support would be required for each.

I could also see gaming and 3D modelling applications being two other use cases.