ShrlAlgoToolkit/WPFluent/Layout/WaterfallPanel.cs

using System;
using System.Linq;
using System.Windows.Controls;

namespace WPFluent.Layout;

public class WaterfallPanel : VirtualizingPanel
{
    public static readonly DependencyProperty ColumnsProperty =
        DependencyProperty.Register(nameof(Columns), typeof(int), typeof(WaterfallPanel), new PropertyMetadata(3));

    public static readonly DependencyProperty SpacingProperty =
        DependencyProperty.Register(nameof(Spacing), typeof(double), typeof(WaterfallPanel), new PropertyMetadata(5.0));
    private List<double> columnHeights = [];

    protected override Size MeasureOverride(Size availableSize)
    {
        columnHeights.Clear();
        var panelDesiredSize = new Size(0, 0);
        columnHeights = new double[Columns].ToList();
        double currentX = 0;
        var width = availableSize.Width / Columns - (Columns * Spacing);
        for(var i = 0; i < InternalChildren.Count; i++)
        {
            if(InternalChildren[i] is not FrameworkElement child)
                continue;
            child.Measure(availableSize);
            child.Width = width;
            var columnIndex = i % Columns;
            var x = columnIndex != 0 ? currentX + Spacing : 0;
            var y = columnHeights[columnIndex];
            if(i >= Columns)
                y = y + Spacing;
            var size = new Size(width, child.DesiredSize.Height);
            child.Arrange(new Rect(new Point(x, y), size));
            panelDesiredSize.Width = Math.Max(panelDesiredSize.Width, x + child.DesiredSize.Width);
            panelDesiredSize.Height = Math.Max(panelDesiredSize.Height, y + child.DesiredSize.Height);
            currentX = x + size.Width;
            if(currentX >= Width)
                currentX = 0;
            columnHeights[columnIndex] += child.DesiredSize.Height + (i >= Columns ? Spacing : 0);
        }
        return panelDesiredSize;
    }

    public void AddChild(UIElement element) { Children.Add(element); }

    public int Columns { get { return (int)GetValue(ColumnsProperty); } set { SetValue(ColumnsProperty, value); } }

    public double Spacing
    {
        get { return (double)GetValue(SpacingProperty); }
        set { SetValue(SpacingProperty, value); }
    }
}