WPF Rendering Architecture

Rendering Pipeline Overview

User Input → Property Change → InvalidateXxx()
                ↓
        ┌───────────────┐
        │ Measure Pass  │ → Determines DesiredSize
        ├───────────────┤
        │ Arrange Pass  │ → Determines ActualSize/Position
        ├───────────────┤
        │ Render Pass   │ → OnRender() / DrawingContext
        └───────────────┘
                ↓
    Composition Tree → MILCore → DirectX → GPU

1. Layout Passes

Invalidation Methods

| Method | Triggers | Use When | |--------|----------|----------| | InvalidateMeasure() | Measure + Arrange + Render | Size might change | | InvalidateArrange() | Arrange + Render | Position might change | | InvalidateVisual() | Render only | Visual appearance change |

FrameworkPropertyMetadata Flags

public static readonly DependencyProperty RadiusProperty =
    DependencyProperty.Register("Radius", typeof(double), typeof(MyControl),
        new FrameworkPropertyMetadata(10.0,
            FrameworkPropertyMetadataOptions.AffectsRender |
            FrameworkPropertyMetadataOptions.AffectsMeasure));

| Flag | Effect | |------|--------| | AffectsMeasure | Triggers Measure pass | | AffectsArrange | Triggers Arrange pass | | AffectsRender | Triggers Render pass | | AffectsParentMeasure | Parent re-measures | | AffectsParentArrange | Parent re-arranges |

Custom Control Layout

protected override Size MeasureOverride(Size availableSize)
{
    // Calculate desired size based on content
    double width = Math.Min(200, availableSize.Width);
    double height = Math.Min(100, availableSize.Height);
    return new Size(width, height);
}

protected override Size ArrangeOverride(Size finalSize)
{
    // Position children within finalSize
    foreach (UIElement child in Children)
    {
        child.Arrange(new Rect(0, 0, finalSize.Width, finalSize.Height));
    }
    return finalSize;
}

protected override void OnRender(DrawingContext dc)
{
    dc.DrawRectangle(Background, null, new Rect(RenderSize));
}

2. Hardware Acceleration

Rendering Tiers

| Tier | GPU Memory | Features | |------|-----------|----------| | 0 | < 30MB | Software rendering | | 1 | 30-120MB | Partial hardware (no PS 2.0) | | 2 | ≥ 120MB | Full hardware acceleration |

int tier = RenderCapability.Tier >> 16;
// 0 = Software, 1 = Partial, 2 = Full GPU

Software Fallback Conditions

WPF falls back to software rendering when:

• GPU memory insufficient
• Texture > 8192px
• Remote Desktop (RDP) session
• AllowsTransparency="True" on Window
• Legacy BitmapEffect used

RenderOptions Optimization

// For images that will be scaled
RenderOptions.SetBitmapScalingMode(image, BitmapScalingMode.LowQuality);

// For pixel-perfect lines
RenderOptions.SetEdgeMode(element, EdgeMode.Aliased);

// For tiled brushes
RenderOptions.SetCachingHint(brush, CachingHint.Cache);
RenderOptions.SetCacheInvalidationThresholdMinimum(brush, 0.5);
RenderOptions.SetCacheInvalidationThresholdMaximum(brush, 2.0);

3. Performance Optimization

Batch Updates Pattern

// Bad: Multiple layout passes
for (int i = 0; i < 100; i++)
{
    items[i].Width = newWidths[i]; // Each triggers layout
}

// Good: Single layout pass
using (Dispatcher.DisableProcessing())
{
    for (int i = 0; i < 100; i++)
    {
        items[i].Width = newWidths[i];
    }
} // Layout happens once here

Common Performance Issues

| Problem | Cause | Solution | |---------|-------|----------| | Slow scrolling | Deep Visual Tree | Virtualization | | Layout thrashing | Frequent InvalidateMeasure | Batch updates | | Slow startup | Complex Grid | Simplify layout | | Memory growth | BitmapEffect | Use Effect class |

4. Tier-Adaptive Rendering

public void ConfigureForTier()
{
    int tier = RenderCapability.Tier >> 16;

    if (tier < 2)
    {
        // Disable expensive effects
        DisableDropShadows();
        DisableAnimations();
        UseSimplifiedVisuals();
    }
}