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fix(TextAreaControl): do not cache the measuring device context #64

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Merged
mstv merged 1 commit into from
Sep 20, 2026
Merged

fix(TextAreaControl): do not cache the measuring device context #64

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50 changes: 25 additions & 25 deletions Project/Src/Gui/TextAreaControl.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -35,13 +35,6 @@ public class TextAreaControl : Panel

private int[] lineLengthCache;

/// <summary>
/// Kept for the lifetime of the control so that measuring line widths does not create a
/// device context per layout pass. Created on first use, because the handle it needs does
/// not exist yet while the control is being constructed.
/// </summary>
private Graphics measureGraphics;

private TextEditorControl motherTextEditorControl;
private Point scrollToPosOnNextUpdate;

Expand Down Expand Up @@ -114,12 +107,6 @@ protected override void Dispose(bool disposing)
hRuler.Dispose();
hRuler = null;
}

if (measureGraphics != null)
{
measureGraphics.Dispose();
measureGraphics = null;
}
}

base.Dispose(disposing);
Expand Down Expand Up @@ -294,24 +281,37 @@ static ScrollVisibilities GetScrollVisibilities(bool h, bool v)
lineLengthCache = new int[lastLineIndex + LineLengthCacheAdditionalSize];

var maxLength = 0;
for (var lineIndex = firstLineIndex; lineIndex <= lastLineIndex; lineIndex++)

// The device context must not outlive this layout pass: a Graphics from
// Control.CreateGraphics() is bound to the control's current window handle and to a DC
// borrowed from the system cache, so keeping it across calls leaves a stale HDC which
// makes TextRenderer.MeasureText throw "Parameter is not valid".
Graphics measureGraphics = null;
Comment on lines +285 to +289

@mstv mstv Sep 19, 2026

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What about discarding measureGraphics on hide?

try
{
var lineSegment = Document.GetLineSegment(lineIndex);
if (Document.FoldingManager.IsLineVisible(lineIndex))
for (var lineIndex = firstLineIndex; lineIndex <= lastLineIndex; lineIndex++)
{
if (lineLengthCache[lineIndex] > 0)
{
maxLength = Math.Max(maxLength, lineLengthCache[lineIndex]);
}
else
var lineSegment = Document.GetLineSegment(lineIndex);
if (Document.FoldingManager.IsLineVisible(lineIndex))
{
measureGraphics ??= TextArea.CreateGraphics();
var visualLength = view.GetVisualWidthColumns(measureGraphics, lineSegment);
lineLengthCache[lineIndex] = Math.Max(1, visualLength);
maxLength = Math.Max(maxLength, visualLength);
if (lineLengthCache[lineIndex] > 0)
{
maxLength = Math.Max(maxLength, lineLengthCache[lineIndex]);
}
else
{
measureGraphics ??= TextArea.CreateGraphics();
var visualLength = view.GetVisualWidthColumns(measureGraphics, lineSegment);
lineLengthCache[lineIndex] = Math.Max(1, visualLength);
maxLength = Math.Max(maxLength, visualLength);
}
}
}
}
finally
{
measureGraphics?.Dispose();
}

var hScrollBarVisible = HScrollBar.Value != 0 || maxLength > visibleColumnCount || (hScrollBarVisibleNow && VScrollBar.IsMouseDown);
vScrollBarVisible = vScrollBarVisible || (hScrollBarVisible && hScrollBarWouldCauseVScrollBar);
Expand Down