tui-cs/Terminal.Gui · warning · ArgumentException

0 length lines are not supported

Error message

0 length lines are not supported

What it means

Thrown by the private helper GetLineEndOnDiffAxis when a line's length is exactly zero. Zero-length lines have no extent on the differing axis, so endpoint computation is undefined. It is an ArgumentException. In normal Exclude flow, zero-length exclusion lines and zero-length collection lines are filtered out before this helper runs, so this guard is effectively an internal invariant that should be unreachable through public API use.

Source

Thrown at Terminal.Gui/Drawing/LineCanvas/StraightLineExtensions.cs:190

    /// <summary>
    ///     <para>
    ///         Calculates the single digit point where a line ends on the differing axis i.e. the maximum (controlling for
    ///         negative lengths).
    ///     </para>
    ///     <para>
    ///         For lines with <see cref="Orientation.Horizontal"/> this is an x coordinate. For lines that are
    ///         <see cref="Orientation.Vertical"/> this is a y coordinate.
    ///     </para>
    /// </summary>
    /// <param name="start">Where the line starts</param>
    /// <param name="length">Length of the line</param>
    /// <param name="orientation">Orientation of the line</param>
    /// <returns>The maximum x or y (whichever is differing) point on the line, controlling for negative lengths. </returns>
    private static int GetLineEndOnDiffAxis (Point start, int length, Orientation orientation)
    {
        if (length == 0)
        {
            throw new ArgumentException (@"0 length lines are not supported", nameof (length));
        }

        int sub = length > 0 ? 1 : -1;

        if (orientation == Orientation.Vertical)
        {
            // Points on line differ by y
            return Math.Max (start.Y + length - sub, start.Y);
        }

        // Points on line differ by x
        return Math.Max (start.X + length - sub, start.X);
    }

    /// <summary>
    ///     <para>
    ///         Calculates the single digit point where a line starts on the differing axis i.e. the minimum (controlling for
    ///         negative lengths).

View on GitHub (pinned to 2e47b11478)

Solutions

1. Do not create StraightLine objects with Length == 0; use Length >= 1 or omit the line.
2. Filter zero-length lines from your collection before calling LineCanvas/Exclude.
3. If hit unexpectedly, file a bug: the public API is supposed to guard this.

Example fix

// before
canvas.AddLine(new StraightLine(start, 0, Orientation.Horizontal, style));

// after
if (length > 0)
    canvas.AddLine(new StraightLine(start, length, Orientation.Horizontal, style));

lines = lines.Where(l => l.Length != 0);

static bool HasNoZeroLengthLines(IEnumerable<StraightLine> lines) => lines.All(l => l.Length != 0);

When it happens

Trigger: Directly causing a StraightLine with Length == 0 to reach endpoint computation. Under the public Exclude API this is guarded (length==0 returns early; collection lines with Length==0 are skipped), so it indicates either an internal bug or a future caller bypassing the guards.

Common situations: Constructing StraightLine instances with Length 0 and passing them into LineCanvas operations that compute endpoints; or a regression in the Exclude guard logic.

Related errors

• At least one color stop must be provided.
• Steps must be greater than 0.
• Number of steps must be N-1
• start must be greater than or equal to 0
• AdornmentView can only render to their Parent or Parent's Su

AI-assisted analysis of tui-cs/Terminal.Gui@2e47b11478 (2026-08-13). Data as JSON: /api/errors/ce6bb97834f3da6e. Report an issue: GitHub.