--- name: rendering-wpf-high-performance description: Provides high-performance WPF rendering techniques including DrawingVisual, WriteableBitmap, CompositionTarget.Rendering, and BitmapCache. Use when implementing real-time graphics, game loops, particle systems, charts, or when Shape controls cause performance issues. --- # High-Performance WPF Rendering ## Quick Reference | Technique | Use Case | Performance | |-----------|----------|-------------| | DrawingVisual | 1K-100K shapes | 10-50x faster than Shape | | WriteableBitmap | Pixel manipulation, heatmaps | Fastest for raw pixels | | CompositionTarget.Rendering | Game loops, real-time animation | ~60 FPS frame callback | | BitmapCache | Complex static visuals | GPU texture caching | ## 1. DrawingVisual Pattern Lightweight visual for high-volume rendering without layout overhead. ```csharp public class ChartVisual : FrameworkElement { private readonly VisualCollection _visuals; public ChartVisual() => _visuals = new VisualCollection(this); public void Render(IEnumerable points) { _visuals.Clear(); var visual = new DrawingVisual(); using (var dc = visual.RenderOpen()) { var pen = new Pen(Brushes.Blue, 1); pen.Freeze(); var prev = points.First(); foreach (var pt in points.Skip(1)) { dc.DrawLine(pen, prev, pt); prev = pt; } } _visuals.Add(visual); } protected override int VisualChildrenCount => _visuals.Count; protected override Visual GetVisualChild(int index) => _visuals[index]; } ``` **Key Points:** - Always `Freeze()` Brush\/Pen for thread safety and performance - Use `StreamGeometry` instead of `PathGeometry` for read-only paths - Override `VisualChildrenCount` and `GetVisualChild` ## 2. WriteableBitmap Pattern Direct pixel manipulation for maximum performance. ```csharp public class PixelCanvas : Image { private WriteableBitmap _bitmap; public void Initialize(int width, int height) { _bitmap = new WriteableBitmap(width, height, 96, 96, PixelFormats.Bgra32, null); Source = _bitmap; } public unsafe void DrawPixel(int x, int y, Color color) { _bitmap.Lock(); try { var ptr = (byte*)_bitmap.BackBuffer; int stride = _bitmap.BackBufferStride; int offset = y * stride + x * 4; ptr[offset + 0] = color.B; ptr[offset + 1] = color.G; ptr[offset + 2] = color.R; ptr[offset + 3] = color.A; _bitmap.AddDirtyRect(new Int32Rect(x, y, 1, 1)); } finally { _bitmap.Unlock(); } } } ``` **Key Points:** - Enable `true<\/AllowUnsafeBlocks>` in .csproj - Use `AddDirtyRect` for partial updates - BGRA32 format: Blue, Green, Red, Alpha order ## 3. CompositionTarget.Rendering Per-frame callback for game loops and real-time updates. ```csharp public class GameLoop { private TimeSpan _lastRender; public void Start() { CompositionTarget.Rendering += OnRendering; } public void Stop() { CompositionTarget.Rendering -= OnRendering; } private void OnRendering(object sender, EventArgs e) { var args = (RenderingEventArgs)e; \/\/ Skip duplicate frames if (args.RenderingTime == _lastRender) return; var deltaTime = (args.RenderingTime - _lastRender).TotalSeconds; _lastRender = args.RenderingTime; Update(deltaTime); Render(); } private void Update(double dt) { \/* Physics, AI *\/ } private void Render() { \/* Drawing *\/ } } ``` **Critical:** Always unsubscribe in `Unloaded` event to prevent memory leaks. ## 4. BitmapCache GPU-cached rendering for complex but static visuals. ```xml <\/Border.CacheMode> <\/Border> ``` ```csharp element.CacheMode = new BitmapCache { RenderAtScale = 1.0 }; ``` **When to Use:** - ✅ Transform animations (rotate, scale, translate) - ✅ Complex PathGeometry, DrawingVisual - ❌ Frequently changing content - ❌ Simple shapes (Rectangle, Ellipse) ## Performance Comparison | Method | 10K Points | Use Case | |--------|-----------|----------| | Shape (Ellipse) | ~500ms | <100 elements | | DrawingVisual | ~20ms | 1K-100K shapes | | WriteableBitmap (managed) | ~5ms | Pixel grids | | WriteableBitmap (unsafe) | ~1ms | Real-time heatmaps | ## Related References For detailed implementation patterns, see: - [reference\/drawingvisual-advanced.md](reference\/drawingvisual-advanced.md) - Hit testing, transforms - [reference\/writeablebitmap-algorithms.md](reference\/writeablebitmap-algorithms.md) - Bresenham, flood fill - [reference\/compositiontarget-examples.md](reference\/compositiontarget-examples.md) - Particle systems - [reference\/bitmapcache-optimization.md](reference\/bitmapcache-optimization.md) - Memory management