Canvas LayoutTransform获取实际比例

Question

我正在使用this example (只使用布局转换，并使用附加行为而不是外部nuget包)来放大我的画布。到目前为止，它似乎还行得通，但我也想限制应用的缩放因子，例如，用户不能放大超过10倍。

为此，我需要找出应用于画布的实际缩放因子。不幸的是，上面的代码没有使用实际的因子，只在已经缩放的控件上应用了下一个ScaleAt操作。

问:我如何找出已经应用的比例因子，以便能够决定是否应用下一个比例因子？

Extra:如何将此因子公开为附加属性的依赖属性，以便可以对其应用来自xaml的绑定？

编辑-添加的代码示例：

public static class ZoomBehavior
{
    //example from https://stackoverflow.com/questions/46424149/wpf-zoom-canvas-center-on-mouse-position

    #region ZoomFactor
    public static double GetZoomFactor(DependencyObject obj)
    {
        return (double)obj.GetValue(ZoomFactorProperty);
    }
    public static void SetZoomFactor(DependencyObject obj, double value)
    {
        obj.SetValue(ZoomFactorProperty, value);
    }
    // Using a DependencyProperty as the backing store for ZoomFactor.  This enables animation, styling, binding, etc...
    public static readonly DependencyProperty ZoomFactorProperty =
        DependencyProperty.RegisterAttached("ZoomFactor", typeof(double), typeof(ZoomBehavior), new PropertyMetadata(1.05));
    #endregion

    #region ModifierKey       
    public static ModifierKeys? GetModifierKey(DependencyObject obj)
    {
        return (ModifierKeys?)obj.GetValue(ModifierKeyProperty);
    }
    public static void SetModifierKey(DependencyObject obj, ModifierKeys? value)
    {
        obj.SetValue(ModifierKeyProperty, value);
    }
    // Using a DependencyProperty as the backing store for ModifierKey.  This enables animation, styling, binding, etc...
    public static readonly DependencyProperty ModifierKeyProperty =
        DependencyProperty.RegisterAttached("ModifierKey", typeof(ModifierKeys?), typeof(ZoomBehavior), new PropertyMetadata(null));
    #endregion
    public static TransformMode TranformMode { get; set; } = TransformMode.Layout;
    private static Transform _transform;
    private static DesignerCanvas _canvas;

    #region IsZoomable        
    public static bool GetIsZoomable(DependencyObject obj)
    {
        return (bool)obj.GetValue(IsZoomableProperty);
    }
    public static void SetIsZoomable(DependencyObject obj, bool value)
    {
        obj.SetValue(IsZoomableProperty, value);
    }
    // Using a DependencyProperty as the backing store for IsZoomable.  This enables animation, styling, binding, etc...
    public static readonly DependencyProperty IsZoomableProperty =
        DependencyProperty.RegisterAttached(
            "IsZoomable",
            typeof(bool),
            typeof(ZoomBehavior),
            new UIPropertyMetadata(false, OnIsZoomableChanged));
    #endregion

    //#region ScaleMax
    //#region ScaleMin

    private static void OnIsZoomableChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        _canvas = d as DesignerCanvas;
        if (null == _canvas)
        {
            System.Diagnostics.Debug.Assert(false, "Wrong dependency object type");
            return;
        }
        if ((e.NewValue is bool) == false)
        {
            System.Diagnostics.Debug.Assert(false, "Wrong value type assigned to dependency object");
            return;
        }

        if (true == (bool)e.NewValue)
        {
            _canvas.MouseWheel += Canvas_MouseWheel;
            if (TranformMode == TransformMode.Render)
            {
                _transform = _canvas.RenderTransform = new MatrixTransform();
            }
            else
            {
                _transform = _canvas.LayoutTransform = new MatrixTransform();
            }
        }
        else
        {
            _canvas.MouseWheel -= Canvas_MouseWheel;
        }
    }

    private static void Canvas_MouseWheel(object sender, MouseWheelEventArgs e)
    {
        ModifierKeys? modifierkey = GetModifierKey(sender as DependencyObject);

        if (!modifierkey.HasValue)
        {
            return;
        }

        if((Keyboard.Modifiers & (modifierkey.Value)) == ModifierKeys.None)
        {
            return;
        }

        if (!(_transform is MatrixTransform transform))
        {
            return;
        }

        var pos1 = e.GetPosition(_canvas);
        //double max = GetScaleMax(sender as DependencyObject);
        //double min = GetScaleMin(sender as DependencyObject);

        double zoomfactor = GetZoomFactor(sender as DependencyObject);            
        double scale = (e.Delta < 0) ? zoomfactor : (1 / zoomfactor);
        //scale = (scale > max) ? max : scale;
        //scale = (scale < min) ? min : scale;

        var mat = transform.Matrix;            
        mat.ScaleAt(scale, scale, pos1.X, pos1.Y);
        transform.Matrix = mat;
        e.Handled = true;
    }

    public enum TransformMode
    {
        Layout,
        Render,
    }
}

Answer 1

您可以使用Graphics.Transform的m11和m22元素来获得x和y比例因子。你可以在每个维度上进行不同的“缩放”，这就是为什么你会得到两个因子。

但你永远不会知道你的Graphics对象是为了什么而创建的，它们实际上可以堆叠在另一个之上，更好地跟踪你自己在另一个变量上所做的任何缩放操作。