inconsistent scroll simulation

Description

When using the following code, each time the scroll goes roughly to the same place but not exactly, and there is no way to know exactly how much the element was scrolled:

private void scrollTo(int startX, int startY, int endX, int endY) {
    PointerInput finger = new PointerInput(PointerInput.Kind.TOUCH, "finger");
    Sequence scrollAction = new Sequence(finger, 0);
    scrollAction.addAction(finger.createPointerMove(Duration.ofMillis(0), PointerInput.Origin.viewport(), startX, startY));
    scrollAction.addAction(finger.createPointerDown(PointerInput.MouseButton.LEFT.asArg()));
    scrollAction.addAction(finger.createPointerMove(Duration.ofMillis(500), PointerInput.Origin.viewport(), endX, endY));
    // repeat last action as if to make the finger stay in place for 500 ms
    scrollAction.addAction(finger.createPointerMove(Duration.ofMillis(500), PointerInput.Origin.viewport(), endX, endY));
    scrollAction.addAction(finger.createPointerUp(PointerInput.MouseButton.LEFT.asArg()));
}

scrollTo(540, 1579, 540, 172);

On BrowserStack I see the correct request arrives:

[{"id":"finger","type":"pointer","parameters":{"pointerType":"touch"},"actions":[{"duration":0,"x":540,"y":1579,"type":"pointerMove","origin":"viewport"},{"button":0,"type":"pointerDown"},{"duration":500,"x":540,"y":172,"type":"pointerMove","origin":"viewport"},{"duration":500,"x":540,"y":172,"type":"pointerMove","origin":"viewport"},{"button":0,"type":"pointerUp"}]}]

but still each time I run that code on a fresh instance I get a bit different result.

Environment

• Appium version 1.21.0 (on BrowserStack)
• Android version 9.0, Google Pixel 2, UiAutomator2

Details

Please provide more details, if necessary.

Link To Appium Logs

https://gist.github.com/itaibh/d8028aa2f13ce3d16e15194101e9327e

In the Appium logs you’ll see I use the Cancel action, but the result is the same as with lifting the finger.

[mykola-mokhnach]

I would say this behaviour is expected. Basically, what this code is doing, it emulates user touches. And usually these are not 100% precise, because they have some inertia. You could also try mobile: gestures to see if that helps. These are basically shortcuts to actions, just refined by Google and supplied with optimal parameters for each particular gesture type: https://github.com/appium/appium/blob/master/docs/en/writing-running-appium/android/android-mobile-gestures.md

[itaibh]

It didn’t get to the server, the exception was thrown from the Java upon calling the execute command. The server is BrowserStack. The Java bindings are 8.0.0-beta.