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();
}

}