В качестве альтернативного решения (если кто-то найдет этот вопрос позже) для предотвращения масштабирования BorderThickness, вы можете использовать пользовательскую версию Viewbox со специальным конвертером.
Обычный Viewbox, но теперь с возможностью чтения.только Scale свойство и статическое ThicknessConverter:
public class BorderyViewbox : Decorator {
public static readonly DependencyProperty StretchProperty = DependencyProperty.Register(nameof(Stretch),
typeof(Stretch), typeof(BorderyViewbox), new FrameworkPropertyMetadata(Stretch.Uniform, FrameworkPropertyMetadataOptions.AffectsMeasure));
public Stretch Stretch {
get { return (Stretch)GetValue(StretchProperty); }
set { SetValue(StretchProperty, value); }
}
public static readonly DependencyProperty StretchDirectionProperty = DependencyProperty.Register(nameof(StretchDirection),
typeof(StretchDirection), typeof(BorderyViewbox), new FrameworkPropertyMetadata(StretchDirection.Both, FrameworkPropertyMetadataOptions.AffectsMeasure));
public StretchDirection StretchDirection {
get { return (StretchDirection)GetValue(StretchDirectionProperty); }
set { SetValue(StretchDirectionProperty, value); }
}
public static readonly DependencyPropertyKey ScalePropertyKey = DependencyProperty.RegisterReadOnly(nameof(Scale), typeof(Size),
typeof(BorderyViewbox), new PropertyMetadata(default(Size)));
public static readonly DependencyProperty ScaleProperty = ScalePropertyKey.DependencyProperty;
public Size Scale => (Size)GetValue(ScaleProperty);
private ContainerVisual InternalVisual {
get {
if (_internalVisual == null) {
_internalVisual = new ContainerVisual();
AddVisualChild(_internalVisual);
}
return _internalVisual;
}
}
private UIElement InternalChild {
get {
var vc = InternalVisual.Children;
return vc.Count != 0 ? vc[0] as UIElement : null;
}
set {
var vc = InternalVisual.Children;
if (vc.Count != 0) vc.Clear();
vc.Add(value);
}
}
private Transform InternalTransform {
get { return InternalVisual.Transform; }
set { InternalVisual.Transform = value; }
}
public override UIElement Child {
get { return InternalChild; }
set {
var old = InternalChild;
if (!ReferenceEquals(old, value)) {
RemoveLogicalChild(old);
if (value != null) {
AddLogicalChild(value);
}
InternalChild = value;
InvalidateMeasure();
}
}
}
protected override int VisualChildrenCount => 1;
protected override Visual GetVisualChild(int index) {
if (index != 0) throw new ArgumentOutOfRangeException(nameof(index));
return InternalVisual;
}
protected override IEnumerator LogicalChildren => InternalChild == null ? EmptyEnumerator.Instance : new SingleChildEnumerator(InternalChild);
protected override Size MeasureOverride(Size constraint) {
var child = InternalChild;
var parentSize = new Size();
if (child != null) {
var infinteConstraint = new Size(double.PositiveInfinity, double.PositiveInfinity);
child.Measure(infinteConstraint);
var childSize = child.DesiredSize;
var scale = ComputeScaleFactor(constraint, childSize, Stretch, StretchDirection);
SetValue(ScalePropertyKey, scale);
parentSize.Width = scale.Width * childSize.Width;
parentSize.Height = scale.Height * childSize.Height;
}
return parentSize;
}
protected override Size ArrangeOverride(Size arrangeSize) {
var child = InternalChild;
if (child != null) {
var childSize = child.DesiredSize;
var scale = ComputeScaleFactor(arrangeSize, childSize, Stretch, StretchDirection);
SetValue(ScalePropertyKey, scale);
InternalTransform = new ScaleTransform(scale.Width, scale.Height);
child.Arrange(new Rect(new Point(), child.DesiredSize));
arrangeSize.Width = scale.Width * childSize.Width;
arrangeSize.Height = scale.Height * childSize.Height;
}
return arrangeSize;
}
private static Size ComputeScaleFactor(Size availableSize, Size contentSize, Stretch stretch, StretchDirection stretchDirection) {
var scaleX = 1.0;
var scaleY = 1.0;
var isConstrainedWidth = !double.IsPositiveInfinity(availableSize.Width);
var isConstrainedHeight = !double.IsPositiveInfinity(availableSize.Height);
if ((stretch == Stretch.Uniform || stretch == Stretch.UniformToFill || stretch == Stretch.Fill)
&& (isConstrainedWidth || isConstrainedHeight)) {
scaleX = Equals(0d, contentSize.Width) ? 0.0 : availableSize.Width / contentSize.Width;
scaleY = Equals(0d, contentSize.Height) ? 0.0 : availableSize.Height / contentSize.Height;
if (!isConstrainedWidth) {
scaleX = scaleY;
} else if (!isConstrainedHeight) {
scaleY = scaleX;
} else {
switch (stretch) {
case Stretch.Uniform:
var minscale = scaleX < scaleY ? scaleX : scaleY;
scaleX = scaleY = minscale;
break;
case Stretch.UniformToFill:
var maxscale = scaleX > scaleY ? scaleX : scaleY;
scaleX = scaleY = maxscale;
break;
case Stretch.Fill:
break;
}
}
switch (stretchDirection) {
case StretchDirection.UpOnly:
if (scaleX < 1.0) scaleX = 1.0;
if (scaleY < 1.0) scaleY = 1.0;
break;
case StretchDirection.DownOnly:
if (scaleX > 1.0) scaleX = 1.0;
if (scaleY > 1.0) scaleY = 1.0;
break;
case StretchDirection.Both:
break;
}
}
return new Size(scaleX, scaleY);
}
private ContainerVisual _internalVisual;
#region Converter-related stuff
private class ConverterInner : IValueConverter {
public object Convert(object value, Type targetType, object parameter, CultureInfo culture) {
if (!(value is Size)) return parameter;
var scale = (Size)value;
var thickness = parameter as Thickness? ?? new Thickness(1d);
return new Thickness(thickness.Left / scale.Width, thickness.Top / scale.Height,
thickness.Right / scale.Width, thickness.Bottom / scale.Height);
}
public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture) {
if (!(value is Size)) return parameter;
var scale = (Size)value;
var thickness = parameter as Thickness? ?? new Thickness(1d);
return new Thickness(thickness.Left * scale.Width, thickness.Top * scale.Height,
thickness.Right * scale.Width, thickness.Bottom * scale.Height);
}
}
public static IValueConverter ThicknessConverter { get; } = new ConverterInner();
#endregion
}
Пример использования:
<BorderyViewbox x:Name="Viewbox">
<Border BorderBrush="Red" SnapsToDevicePixels="True">
<Border.BorderThickness>
<Binding Path="Scale" ElementName="Viewbox" Converter="{x:Static BorderyViewbox.ThicknessConverter}">
<Binding.ConverterParameter>
<Thickness>3</Thickness>
</Binding.ConverterParameter>
</Binding>
</Border.BorderThickness>
</Border>
</BorderyViewbox>
Укороченная версия с использованием статического ресурса:
<Thickness x:Key="BorderThickness">3</Thickness>
<BorderyViewbox x:Name="Viewbox">
<Border BorderBrush="Red" SnapsToDevicePixels="True"
BorderThickness="{Binding Path=Scale, ElementName=Viewbox,
Converter={x:Static BorderyViewbox.ThicknessConverter},
ConverterParameter={StaticResource BorderThickness}}" />
</BorderyViewbox>