VisualRenderers.cs

using SwiftDotNet;

namespace SwiftDotNet.Graphics;

/// <summary>Context handed to a custom renderer: the node's id/props plus an emit hook.</summary>
public sealed class VisualRenderContext
{
    readonly Action<string, string?> _emit;

    internal VisualRenderContext(string id, IReadOnlyDictionary<string, object?> props, Action<string, string?> emit)
    {
        Id = id;
        Props = props;
        _emit = emit;
    }

    public string Id { get; }
    public IReadOnlyDictionary<string, object?> Props { get; }

    /// <summary>Raise this control's event back to its C# handler.</summary>
    public void Emit(string? value = null) => _emit(Id, value);

    public string String(string key) => Props.TryGetValue(key, out var v) ? v?.ToString() ?? "" : "";
    public double? Number(string key) => Props.TryGetValue(key, out var v) && v is double d ? d : null;
    public bool Bool(string key) => Props.TryGetValue(key, out var v) && v is bool b && b;
}

/// <summary>
/// A custom renderer for a node type on a self-drawing backend. Because the backend owns the pixels, a
/// renderer must both <see cref="Measure"/> (intrinsic size) and <see cref="Paint"/> itself — the
/// self-drawing analog of GTK's <c>Create</c>/<c>Update</c> widget pair.
/// </summary>
public interface IVisualRenderer
{
    Size Measure(VisualRenderContext ctx, Size available);
    void Paint(VisualRenderContext ctx, ICanvas canvas, Rect rect);
}

/// <summary>
/// Registry of custom renderers, keyed by <see cref="CustomView.TypeName"/>. Mirrors
/// <c>GtkRenderers</c>; unregistered types fall back to a ⚠️ placeholder in the interpreter.
/// </summary>
public static class VisualRenderers
{
    static readonly Dictionary<string, IVisualRenderer> Map = new();

    public static void Register(string type, IVisualRenderer renderer) => Map[type] = renderer;

    internal static IVisualRenderer? Get(string type) => Map.GetValueOrDefault(type);
}