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();
    }
}