rendering-mewui-elements— agent skill

Rendering Pipeline

MewUI uses a three-pass layout system:

Measure (calculate DesiredSize) → Arrange (set Bounds) → Render (draw via IGraphicsContext)

Key overrides in custom controls:

• MeasureContent(Size availableSize) → return desired size
• ArrangeContent(Rect bounds) → position children
• OnRender(IGraphicsContext context) → draw visuals

IGraphicsContext Essentials

protected override void OnRender(IGraphicsContext context)
{
    var bounds = new Rect(0, 0, Bounds.Width, Bounds.Height);

    // State management (always Save/Restore)
    context.Save();
    context.Translate(10, 10);
    context.SetClip(clipRect);
    // ... drawing ...
    context.Restore();

    // Drawing primitives
    context.FillRectangle(bounds, Colors.Blue);
    context.DrawRectangle(bounds, Colors.Black, thickness: 1);
    context.FillRoundedRectangle(bounds, radiusX: 4, radiusY: 4, Colors.White);
    context.DrawLine(start, end, Colors.Gray, thickness: 1);
    context.FillEllipse(bounds, Colors.Red);

    // Text - note parameter order: text, bounds, font, color, alignments, wrapping
    context.DrawText("Hello", bounds, font, Colors.Black,
        TextAlignment.Center, TextAlignment.Center, TextWrapping.NoWrap);

    // Images
    context.DrawImage(image, destRect);
}

Text Measurement

protected override Size MeasureContent(Size availableSize)
{
    var factory = GetGraphicsFactory();
    using var ctx = factory.CreateMeasurementContext(GetDpi());  // uint dpi (96, 144, etc.)
    return ctx.MeasureText(Text, GetFont(), availableSize.Width);
}

Graphics Backends

Application.DefaultGraphicsBackend = GraphicsBackend.Direct2D;  // GPU (Windows)
Application.DefaultGraphicsBackend = GraphicsBackend.Gdi;       // Software (Windows)
Application.DefaultGraphicsBackend = GraphicsBackend.OpenGL;    // Cross-platform

Invalidation

InvalidateMeasure();  // Re-measure + re-arrange + re-render
InvalidateArrange();  // Re-arrange + re-render
InvalidateVisual();   // Re-render only

Detailed API: See graphics-api.md Pipeline details: See pipeline.md