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feat: Improve selection handling for buffer trims and scrolling #4

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Merged
tomlm merged 1 commit into from
May 13, 2026
Merged

feat: Improve selection handling for buffer trims and scrolling #4

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98 changes: 98 additions & 0 deletions src/XTerm.NET.Tests/SelectionTests.cs
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Original file line number Diff line number Diff line change
@@ -0,0 +1,98 @@
using XTerm.Options;

namespace XTerm.NET.Tests;

public class SelectionTests
{
[Fact]
public void SelectionText_RemainsAnchored_WhenViewportScrolls()
{
var terminal = new Terminal(new TerminalOptions { Rows = 5, Cols = 80, Scrollback = 100 });

for (int i = 0; i < 20; i++)
{
terminal.WriteLine($"Line{i:00}");
}

terminal.ScrollToTop();
terminal.Selection.StartSelection(4, 2);
terminal.Selection.UpdateSelection(5, 2);
terminal.Selection.EndSelection();

Assert.Equal("02", terminal.Selection.GetSelectionText());

terminal.ScrollLines(1);

Assert.Equal("02", terminal.Selection.GetSelectionText());
}

[Fact]
public void IsCellSelected_TracksBufferSelectionAcrossViewportScroll()
{
var terminal = new Terminal(new TerminalOptions { Rows = 5, Cols = 80, Scrollback = 100 });

for (int i = 0; i < 20; i++)
{
terminal.WriteLine($"Line{i:00}");
}

terminal.ScrollToTop();
terminal.Selection.StartSelection(4, 2);
terminal.Selection.UpdateSelection(5, 2);
terminal.Selection.EndSelection();

Assert.True(terminal.Selection.IsCellSelected(4, 2));
Assert.False(terminal.Selection.IsCellSelected(4, 1));

terminal.ScrollLines(1);

Assert.True(terminal.Selection.IsCellSelected(4, 1));
Assert.False(terminal.Selection.IsCellSelected(4, 2));
}

[Fact]
public void SelectAll_IncludesScrollback_NotJustViewport()
{
var terminal = new Terminal(new TerminalOptions { Rows = 3, Cols = 80, Scrollback = 20 });

for (int i = 0; i < 8; i++)
{
terminal.WriteLine($"Line{i}");
}

terminal.Selection.SelectAll();

var selectedText = terminal.Selection.GetSelectionText();

Assert.Contains("Line0", selectedText);
Assert.Contains("Line7", selectedText);
}

[Fact]
public void Selection_IsCleared_WhenTrimRemovesSelectedLines()
{
var terminal = new Terminal(new TerminalOptions { Rows = 3, Cols = 80, Scrollback = 2 });

for (int i = 0; i < 5; i++)
{
terminal.WriteLine($"Line{i}");
}

terminal.ScrollToTop();
var initialTopLine = terminal.GetVisibleLines()[0];
var expectedSelectedText = initialTopLine[4].ToString();
terminal.Selection.StartSelection(4, 0);
terminal.Selection.UpdateSelection(4, 0);
terminal.Selection.EndSelection();

Assert.Equal(expectedSelectedText, terminal.Selection.GetSelectionText());

for (int i = 5; i < 10; i++)
{
terminal.WriteLine($"Line{i}");
}

Assert.False(terminal.Selection.HasSelection);
Assert.Equal(string.Empty, terminal.Selection.GetSelectionText());
}
}
10 changes: 10 additions & 0 deletions src/XTerm.NET/Buffer/TerminalBuffer.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -65,6 +65,11 @@ public int ViewportY

public CircularList<BufferLine> Lines => _lines;

/// <summary>
/// Fired when lines are trimmed from the start of the buffer.
/// </summary>
public event Action<int>? Trimmed;

/// <summary>
/// Saved cursor state for DECSC/DECRC.
/// </summary>
Expand Down Expand Up @@ -152,6 +157,11 @@ public void ScrollUp(int lines, bool isWrapped = false)
// Push the new line at the end (bottom of screen in buffer terms)
_lines.Push(newLine);

if (willBeRecycled)
{
Trimmed?.Invoke(1);
}

// Only increment yBase if the buffer didn't recycle
if (!willBeRecycled)
{
Expand Down
68 changes: 57 additions & 11 deletions src/XTerm.NET/Selection/SelectionManager.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -36,6 +36,7 @@ public SelectionManager(Terminal terminal)
_terminal = terminal;
_isSelecting = false;
_selectionMode = SelectionMode.Normal;
_terminal.Buffer.Trimmed += HandleTrim;
}

/// <summary>
Expand All @@ -45,8 +46,9 @@ public void StartSelection(int x, int y, SelectionMode mode = SelectionMode.Norm
{
_isSelecting = true;
_selectionMode = mode;
_selectionStart = (x, y);
_selectionEnd = (x, y);
var absoluteY = ToAbsoluteY(y);
_selectionStart = (x, absoluteY);
_selectionEnd = (x, absoluteY);

// Adjust for word or line mode
if (mode == SelectionMode.Word)
Expand All @@ -69,7 +71,7 @@ public void UpdateSelection(int x, int y)
if (!_isSelecting || !_selectionStart.HasValue)
return;

_selectionEnd = (x, y);
_selectionEnd = (x, ToAbsoluteY(y));

// Adjust for selection mode
if (_selectionMode == SelectionMode.Word)
Expand Down Expand Up @@ -109,7 +111,7 @@ public void ClearSelection()
public void SelectAll()
{
_selectionStart = (0, 0);
_selectionEnd = (_terminal.Cols - 1, _terminal.Rows - 1);
_selectionEnd = (_terminal.Cols - 1, Math.Max(_terminal.Buffer.Lines.Length - 1, 0));
_isSelecting = false;
SelectionChanged?.Invoke();
}
Expand All @@ -136,7 +138,10 @@ public string GetSelectionText()

for (int y = start.y; y <= end.y; y++)
{
var line = buffer.Lines[buffer.YDisp + y];
if (y < 0 || y >= buffer.Lines.Length)
continue;

var line = buffer.Lines[y];
if (line == null)
continue;

Expand Down Expand Up @@ -164,6 +169,7 @@ public bool IsCellSelected(int x, int y)
if (!HasSelection)
return false;

var absoluteY = ToAbsoluteY(y);
var start = _selectionStart!.Value;
var end = _selectionEnd!.Value;

Expand All @@ -174,16 +180,16 @@ public bool IsCellSelected(int x, int y)
}

// Check if cell is in selection
if (y < start.y || y > end.y)
if (absoluteY < start.y || absoluteY > end.y)
return false;

if (y == start.y && y == end.y)
if (absoluteY == start.y && absoluteY == end.y)
return x >= start.x && x <= end.x;

if (y == start.y)
if (absoluteY == start.y)
return x >= start.x;

if (y == end.y)
if (absoluteY == end.y)
return x <= end.x;

return true;
Expand All @@ -202,7 +208,7 @@ private void ExpandSelectionToWord()
var end = _selectionEnd.Value;

// Expand start to word boundary
var startLine = buffer.Lines[buffer.YDisp + start.y];
var startLine = start.y >= 0 && start.y < buffer.Lines.Length ? buffer.Lines[start.y] : null;
if (startLine != null)
{
while (start.x > 0 && IsWordChar(startLine[start.x - 1].Content))
Expand All @@ -212,7 +218,7 @@ private void ExpandSelectionToWord()
}

// Expand end to word boundary
var endLine = buffer.Lines[buffer.YDisp + end.y];
var endLine = end.y >= 0 && end.y < buffer.Lines.Length ? buffer.Lines[end.y] : null;
if (endLine != null)
{
while (end.x < _terminal.Cols - 1 && IsWordChar(endLine[end.x + 1].Content))
Expand Down Expand Up @@ -261,6 +267,46 @@ private bool IsWordChar(string ch)
var c = ch[0];
return char.IsLetterOrDigit(c) || c == '_';
}

private int ToAbsoluteY(int viewportY)
{
return _terminal.Buffer.YDisp + viewportY;
}

private void HandleTrim(int amount)
{
if (amount <= 0)
return;

if (_selectionStart.HasValue)
{
_selectionStart = (_selectionStart.Value.x, _selectionStart.Value.y - amount);
}

if (_selectionEnd.HasValue)
{
_selectionEnd = (_selectionEnd.Value.x, _selectionEnd.Value.y - amount);
}

if (_selectionEnd.HasValue && _selectionEnd.Value.y < 0)
{
ClearSelection();
return;
}

if (_selectionStart.HasValue && _selectionStart.Value.y < 0)
{
_selectionStart = (0, 0);
}

if (_selectionEnd.HasValue)
{
var maxY = Math.Max(_terminal.Buffer.Lines.Length - 1, 0);
_selectionEnd = (_selectionEnd.Value.x, Math.Min(_selectionEnd.Value.y, maxY));
}

SelectionChanged?.Invoke();
}
}

/// <summary>
Expand Down
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