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HtmlPanel: Ctrl+wheel zoom and middle-button pan #247

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HtmlPanel: Ctrl+wheel zoom and middle-button pan #247

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8b3b781
feat: Modernize HtmlRenderer.Core and HtmlRenderer.WinForms for .NET 10
kushanp Jul 6, 2026
981bb4c
chore: bump System.Resources.Extensions to 10.0.10 for .NET 10
kushanp Jul 25, 2026
972b9dd
Add HtmlPanel zoom (Ctrl+wheel) and middle-mouse pan
kushanp Jul 16, 2026
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23 changes: 19 additions & 4 deletions Source/HtmlRenderer.WinForms/Adapters/GraphicsAdapter.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -62,6 +62,12 @@ internal sealed class GraphicsAdapter : RGraphics
/// </summary>
private readonly bool _useGdiPlusTextRendering;

/// <summary>
/// True when <see cref="_g"/> has a non-identity world transform (e.g. zoom ScaleTransform).
/// GDI TextOut ignores the GDI+ world transform, so drawing must use GDI+ in that case.
/// </summary>
private readonly bool _hasWorldTransform;

/// <summary>
/// the initialized HDC used
/// </summary>
Expand Down Expand Up @@ -105,7 +111,13 @@ public GraphicsAdapter(Graphics g, bool useGdiPlusTextRendering, bool releaseGra
_g = g;
_releaseGraphics = releaseGraphics;

_useGdiPlusTextRendering = useGdiPlusTextRendering;
// When a world transform is active (HtmlPanel zoom), force GDI+ for DrawString so text scales.
// Layout measurement still prefers GDI when requested (transform is identity on layout Graphics).
using (var transform = g.Transform)
{
_hasWorldTransform = !transform.IsIdentity;
}
_useGdiPlusTextRendering = useGdiPlusTextRendering || _hasWorldTransform;
}

public override void PopClip()
Expand Down Expand Up @@ -148,7 +160,9 @@ public override void ReturnPreviousSmoothingMode(Object prevMode)

public override RSize MeasureString(string str, RFont font)
{
if (_useGdiPlusTextRendering)
// Prefer GDI metrics when layout has no world transform, even if draw uses GDI+ for zoom.
// Measuring with an active ScaleTransform would inflate sizes and break layout.
if (_useGdiPlusTextRendering && !_hasWorldTransform)
{
ReleaseHdc();
var fontAdapter = (FontAdapter)font;
Expand Down Expand Up @@ -187,7 +201,7 @@ public override void MeasureString(string str, RFont font, double maxWidth, out
{
charFit = 0;
charFitWidth = 0;
if (_useGdiPlusTextRendering)
if (_useGdiPlusTextRendering && !_hasWorldTransform)
{
ReleaseHdc();

Expand Down Expand Up @@ -216,7 +230,8 @@ public override void MeasureString(string str, RFont font, double maxWidth, out

public override void DrawString(string str, RFont font, RColor color, RPoint point, RSize size, bool rtl)
{
if (_useGdiPlusTextRendering)
// GDI TextOut ignores Graphics.ScaleTransform; use GDI+ whenever a world transform is active (zoom).
if (_useGdiPlusTextRendering || _hasWorldTransform)
{
ReleaseHdc();
SetRtlAlignGdiPlus(rtl);
Expand Down
2 changes: 1 addition & 1 deletion Source/HtmlRenderer.WinForms/Adapters/WinFormsAdapter.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -88,7 +88,7 @@ protected override RBrush CreateLinearGradientBrush(RRect rect, RColor color1, R
return new BrushAdapter(new LinearGradientBrush(Utils.Convert(rect), Utils.Convert(color1), Utils.Convert(color2), (float)angle), true);
}

protected override RImage ConvertImageInt(object image)
protected override RImage? ConvertImageInt(object? image)
{
return image != null ? new ImageAdapter((Image)image) : null;
}
Expand Down
12 changes: 6 additions & 6 deletions Source/HtmlRenderer.WinForms/HtmlContainer.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -286,15 +286,15 @@ public SizeF ActualSize
/// <summary>
/// Get the currently selected text segment in the html.
/// </summary>
public string SelectedText
public string? SelectedText
{
get { return _htmlContainerInt.SelectedText; }
}

/// <summary>
/// Copy the currently selected html segment with style.
/// </summary>
public string SelectedHtml
public string? SelectedHtml
{
get { return _htmlContainerInt.SelectedHtml; }
}
Expand All @@ -312,7 +312,7 @@ public void ClearSelection()
/// </summary>
/// <param name="htmlSource">the html to init with, init empty if not given</param>
/// <param name="baseCssData">optional: the stylesheet to init with, init default if not given</param>
public void SetHtml(string htmlSource, CssData baseCssData = null)
public void SetHtml(string? htmlSource, CssData? baseCssData = null)
{
_htmlContainerInt.SetHtml(htmlSource, baseCssData);
}
Expand All @@ -322,7 +322,7 @@ public void SetHtml(string htmlSource, CssData baseCssData = null)
/// </summary>
/// <param name="styleGen">Optional: controls the way styles are generated when html is generated (default: <see cref="HtmlGenerationStyle.Inline"/>)</param>
/// <returns>generated html</returns>
public string GetHtml(HtmlGenerationStyle styleGen = HtmlGenerationStyle.Inline)
public string? GetHtml(HtmlGenerationStyle styleGen = HtmlGenerationStyle.Inline)
{
return _htmlContainerInt.GetHtml(styleGen);
}
Expand All @@ -334,7 +334,7 @@ public string GetHtml(HtmlGenerationStyle styleGen = HtmlGenerationStyle.Inline)
/// <param name="location">the location to find the attribute at</param>
/// <param name="attribute">the attribute key to get value by</param>
/// <returns>found attribute value or null if not found</returns>
public string GetAttributeAt(Point location, string attribute)
public string? GetAttributeAt(Point location, string attribute)
{
return _htmlContainerInt.GetAttributeAt(Utils.Convert(location), attribute);
}
Expand All @@ -358,7 +358,7 @@ public List<LinkElementData<RectangleF>> GetLinks()
/// </summary>
/// <param name="location">the location to find the link at</param>
/// <returns>css link href if exists or null</returns>
public string GetLinkAt(Point location)
public string? GetLinkAt(Point location)
{
return _htmlContainerInt.GetLinkAt(Utils.Convert(location));
}
Expand Down
24 changes: 10 additions & 14 deletions Source/HtmlRenderer.WinForms/HtmlLabel.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -75,7 +75,7 @@ public class HtmlLabel : Control
/// <summary>
/// Underline html container instance.
/// </summary>
protected HtmlContainer _htmlContainer;
protected HtmlContainer? _htmlContainer;

/// <summary>
/// The current border style of the control
Expand All @@ -85,17 +85,17 @@ public class HtmlLabel : Control
/// <summary>
/// the raw base stylesheet data used in the control
/// </summary>
protected string _baseRawCssData;
protected string? _baseRawCssData;

/// <summary>
/// the base stylesheet data used in the panel
/// </summary>
protected CssData _baseCssData;
protected CssData? _baseCssData;

/// <summary>
/// the current html text set in the control
/// </summary>
protected string _text;
protected string? _text;

/// <summary>
/// is to handle auto size of the control height only
Expand Down Expand Up @@ -296,7 +296,7 @@ public virtual bool IsContextMenuEnabled
[Description("Set base stylesheet to be used by html rendered in the control.")]
[Category("Appearance")]
[DesignerSerializationVisibility(DesignerSerializationVisibility.Visible)]
[Editor("System.ComponentModel.Design.MultilineStringEditor, System.Design, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a", "System.Drawing.Design.UITypeEditor, System.Drawing, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a")]
[Editor("System.ComponentModel.Design.MultilineStringEditor, System.Windows.Forms.Design, Version=10.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089", "System.Drawing.Design.UITypeEditor, System.Windows.Forms, Version=10.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089")]
public virtual string BaseStylesheet
{
get { return _baseRawCssData; }
Expand Down Expand Up @@ -488,21 +488,17 @@ protected override void OnLayout(LayoutEventArgs levent)
{
if (_htmlContainer != null)
{
Graphics g = CreateGraphics();
if (g != null)
using (var g = CreateGraphics())
using (var ig = new GraphicsAdapter(g, _htmlContainer.UseGdiPlusTextRendering))
{
using (g)
using (var ig = new GraphicsAdapter(g, _htmlContainer.UseGdiPlusTextRendering))
{
var newSize = HtmlRendererUtils.Layout(ig,
var newSize = HtmlRendererUtils.Layout(ig,
_htmlContainer.HtmlContainerInt,
new RSize(ClientSize.Width - Padding.Horizontal, ClientSize.Height - Padding.Vertical),
new RSize(MinimumSize.Width - Padding.Horizontal, MinimumSize.Height - Padding.Vertical),
new RSize(MaximumSize.Width - Padding.Horizontal, MaximumSize.Height - Padding.Vertical),
AutoSize,
AutoSizeHeightOnly);
ClientSize = Utils.ConvertRound(new RSize(newSize.Width + Padding.Horizontal, newSize.Height + Padding.Vertical));
}
ClientSize = Utils.ConvertRound(new RSize(newSize.Width + Padding.Horizontal, newSize.Height + Padding.Vertical));
}
}
base.OnLayout(levent);
Expand Down Expand Up @@ -659,7 +655,7 @@ protected override void WndProc(ref Message m)
try
{
// Replace .NET's hand cursor with the OS cursor
Win32Utils.SetCursor(Win32Utils.LoadCursor(0, Win32Utils.IdcHand));
Win32Utils.SetCursor(Win32Utils.LoadCursor(IntPtr.Zero, Win32Utils.IdcHand));
m.Result = IntPtr.Zero;
return;
}
Expand Down
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