rendering-with-drawingvisual

# WPF DrawingVisual Patterns

DrawingVisual is a lightweight visual element faster than Shape, suitable for large-scale rendering.

## 1. Visual Hierarchy

```
Visual (abstract)
├── UIElement
│   └── FrameworkElement
│       └── Shape (heavyweight, event support)
│
├── DrawingVisual       ← Lightweight, no events, direct rendering
├── ContainerVisual     ← Groups multiple Visuals
└── HostVisual          ← Cross-thread Visual
```

---

## 2. DrawingVisual vs Shape

| Aspect | DrawingVisual | Shape |
|--------|--------------|-------|
| **Overhead** | Low | High |
| **Layout** | Non-participating | Participating |
| **Events** | Manual implementation | Built-in support |
| **Data binding** | Not available | Available |
| **Use case** | Large elements, performance critical | Interactive UI |

---

## 3. Basic DrawingVisual Host

### 3.1 FrameworkElement Host

```csharp
namespace MyApp.Controls;

using System.Collections.Generic;
using System.Windows;
using System.Windows.Media;

/// <summary>
/// Control that hosts DrawingVisual
/// </summary>
public sealed class DrawingVisualHost : FrameworkElement
{
    private readonly List<Visual> _visuals = [];

    protected override int VisualChildrenCount => _visuals.Count;

    protected override Visual GetVisualChild(int index)
    {
        return _visuals[index];
    }

    /// <summary>
    /// Add Visual
    /// </summary>
    public void AddVisual(Visual visual)
    {
        _visuals.Add(visual);
        AddVisualChild(visual);
        AddLogicalChild(visual);
    }

    /// <summary>
    /// Remove Visual
    /// </summary>
    public void RemoveVisual(Visual visual)
    {
        _visuals.Remove(visual);
        RemoveVisualChild(visual);
        RemoveLogicalChild(visual);
    }

    /// <summary>
    /// Remove all Visuals
    /// </summary>
    public void ClearVisuals()
    {
        foreach (var visual in _visuals)
        {
            RemoveVisualChild(visual);
            RemoveLogicalChild(visual);
        }