Textgrid CursorLocationForPosition reports wrong location when scrolled

[redawl]

Checklist

• I have searched the issue tracker for open issues that relate to the same problem, before opening a new one.
• This issue only relates to a single bug. I will open new issues for any other problems.

Describe the bug

While implementing text highlighting inside a textgrid, I noticed that Textgrid.CursorLocationForPosition reports the incorrect row and col when the widget is scrolled away from the default location. This causes highlighting of the incorrect cell.

This is when using any Scroll, besides fyne.ScrollNone

How to reproduce

1. Create a custom widget using Textgrid as the BaseWidget. Instantiate TextGrid with a Scroll of ScrollBoth, ScrollHorizontalOnly, or ScrollVerticalOnly.
2. Implement the Hoverable interface, and log the result of CursorLocationForPosition in the MouseMoved handler.
3. Observe that the Cursor location reported is correct when the widget is not scrolled from the default location, but is incorrect when scrolled away from the default location.

Screenshots

No response

Example code

package main

import (
	"fmt"

	"fyne.io/fyne/v2"
	"fyne.io/fyne/v2/app"
	"fyne.io/fyne/v2/container"
	"fyne.io/fyne/v2/driver/desktop"
	"fyne.io/fyne/v2/widget"
)

var _ desktop.Hoverable = (*TextgridWrapper)(nil)

type TextgridWrapper struct {
	widget.TextGrid
}

func (t *TextgridWrapper) MouseIn (evt *desktop.MouseEvent) {}
func (t * TextgridWrapper) MouseMoved(evt *desktop.MouseEvent) {
	row, col := t.CursorLocationForPosition(evt.Position)
	fmt.Printf("Reported location: row = %d, col = %d\n", row, col)
}
func (t *TextgridWrapper) MouseOut() {}

func main() {
	a := app.New()
	w := a.NewWindow("Test")
	longText := "dawdawdadddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddd" // Put some looooong text in here...


	textGridWrapper := &TextgridWrapper{
		TextGrid: widget.TextGrid{
			Scroll: fyne.ScrollBoth,
		},
	}
	label := widget.NewLabel(longText[0:len(longText) / 2])
	textGridWrapper.SetText(longText)
	layout := container.NewBorder(label, nil, nil, nil, textGridWrapper)

	w.SetContent(layout)
	w.ShowAndRun()
}

Fyne version

v2.6.0

Go compiler version

1.24.2

Operating system and version

Gentoo

Additional Information

I do currently have a workaround. I implemented a wrapper CursorLocationForPosition for my custom widget that extends Textgrid:

func (p *PacketEntry) CursorLocationForPosition(pos fyne.Position) (row, col int) {
	cellSize := p.TextGrid.PositionForCursorLocation(1, 1)
	y := pos.Y
	x := pos.X

	if p.scroll != nil && p.scroll.Visible() {
		y += p.scroll.Offset.Y
		x += p.scroll.Offset.X
	}

	row = int(y / cellSize.Y)
	col = int(x / cellSize.X)
	return
}

This requires using an external container.Scroll, instead of the one embedded in Textgrid.

While debugging, I noticed that regardless of the scroll visually, the internal Textgrid scroll X and Y are always 0. I think that is part of the issue, but the calculation used is also incorrect.

[andydotxyz]

While debugging, I noticed that regardless of the scroll visually, the internal Textgrid scroll X and Y are always 0. I think that is part of the issue, but the calculation used is also incorrect.

As an extended TextGrid your code won't have access to the internal Scroll... If you are managing to access some offset variable it will likely be a local copy shadowing the internal one. If the scroll offset was always 0 then the content would not scroll...

[redawl]

While debugging, I noticed that regardless of the scroll visually, the internal Textgrid scroll X and Y are always 0. I think that is part of the issue, but the calculation used is also incorrect.

As an extended TextGrid your code won't have access to the internal Scroll... If you are managing to access some offset variable it will likely be a local copy shadowing the internal one. If the scroll offset was always 0 then the content would not scroll...

Thanks for the quick response!

Sorry for the confusion, I was referring to the private scroll property on the wrapped Textgrid. It was always showing the Offset as 0, 0, even though scrolling was working visually as expected. I was using a local copy of fyne where I had added a debug log for the offset when calling CursorLocationForPosition.

It's possible it was user error on my part though if you aren't seeing the same thing.

[andydotxyz]

I was referring to the private scroll property on the wrapped Textgrid

You'll not get access to a private variable when wrapping I don't think - you'd have to put the debugger / println inside the TextGrid code itself.

[redawl]

I was referring to the private scroll property on the wrapped Textgrid

You'll not get access to a private variable when wrapping I don't think - you'd have to put the debugger / println inside the TextGrid code itself.

You are correct. That's why I was using a local fork of fyne, where I added a println in Textgrids CursorLocationForPosition

[andydotxyz]

Fixed on develop and will be on the next release