Incorrect clipping behavior when scroll containers are nested

[charlesdaniels]

Describe the bug:

When a scroll container is nested within another scroll container, the clipping behavior is incorrect.

According to @andydotxyz:

There is a known issue where a scrollContainer inside a ScrollContainer does not clip correctly

I know what the issue is (child clip should intersect parent rather than replace it - but I have not found time to resolve it

The attached video shows a list (which includes a scroll container), where the list items are cards which have scroll containers in their content. Notice how as the outer container is scrolled, the content is not clipped properly and is displayed inside of the menu bar.

vokoscreenNG-2020-12-23_13-00-52.mp4

I have tested this with Fyne v 1.4.2 on Linux with Go 1.15.6.

[andydotxyz]

Easy replicate code:

package main

import (
	"fyne.io/fyne/app"
	"fyne.io/fyne/container"
	"fyne.io/fyne/widget"
)

func main() {
	a := app.New()
	w := a.NewWindow("Hello")

	w.SetContent(container.NewVScroll(
			container.NewVBox(
				container.NewHScroll(widget.NewLabel("FirstFirstFirst")),
				container.NewHScroll(widget.NewLabel("SecondSecondSecond")),
				container.NewHScroll(widget.NewLabel("ThirdThirdThird")),
				container.NewHScroll(widget.NewLabel("FourthFourthFourth")),
			),
		),
	)

	w.ShowAndRun()
}

[andydotxyz]

I have the solution ready to roll - but it uncovered some bad mathis in the gomobile iOS driver that I will have to fix first.

[andydotxyz]

Fixed on release/v1.4.x