BlazorRenderSurfaceComponentBase.cs

using Microsoft.AspNetCore.Components;
using Microsoft.AspNetCore.Components.Web;
 
namespace Gondwana.Blazor.Rendering;

public abstract class BlazorRenderSurfaceComponentBase : ComponentBase, IDisposable
{
    internal virtual Gondwana.Rendering.RenderSurfaceAdapterBase? InputSurfaceAdapter => null;
 
    internal System.Drawing.Point ToScreenPx(double x, double y)
        => InputSurfaceAdapter?.AdapterPxToScreenPx(new System.Drawing.PointF((float)x, (float)y))
           ?? new System.Drawing.Point((int)Math.Floor(x), (int)Math.Floor(y));
 
    private const string DefaultCanvasStyle =
        "width: 100%; height: 100%; display: block; outline: none;";
 
    internal event Action<KeyboardEventArgs>? KeyDown;
    internal event Action<KeyboardEventArgs>? KeyUp;
    internal event Action<MouseEventArgs>? MouseMove;
    internal event Action<MouseEventArgs>? MouseDown;
    internal event Action<MouseEventArgs>? MouseUp;
    internal event Action<WheelEventArgs>? Wheel;
    internal event Action<TouchEventArgs>? TouchStart;
    internal event Action<TouchEventArgs>? TouchMove;
    internal event Action<TouchEventArgs>? TouchEnd;
    internal event Action<TouchEventArgs>? TouchCancel;

    [Parameter(CaptureUnmatchedValues = true)]
    public Dictionary<string, object>? AdditionalAttributes { get; set; }

    protected IReadOnlyDictionary<string, object>? CanvasAttributes { get; private set; }

    protected string CanvasStyle { get; private set; } = DefaultCanvasStyle;

    protected override void OnParametersSet()
    {
        if (AdditionalAttributes is null)
        {
            CanvasAttributes = null;
            CanvasStyle = DefaultCanvasStyle;
            return;
        }
 
        CanvasStyle = DefaultCanvasStyle;
        if (AdditionalAttributes.TryGetValue("style", out var styleObj) && styleObj is not null)
            CanvasStyle = $"{DefaultCanvasStyle} {styleObj}";
 
        var attributes = new Dictionary<string, object>(
            AdditionalAttributes,
            StringComparer.OrdinalIgnoreCase);
        attributes.Remove("style");
        CanvasAttributes = attributes;
    }

    protected void HandleKeyDown(KeyboardEventArgs e) => KeyDown?.Invoke(e);

    protected void HandleKeyUp(KeyboardEventArgs e) => KeyUp?.Invoke(e);

    protected void HandleMouseMove(MouseEventArgs e) => MouseMove?.Invoke(e);

    protected void HandleMouseDown(MouseEventArgs e) => MouseDown?.Invoke(e);

    protected void HandleMouseUp(MouseEventArgs e) => MouseUp?.Invoke(e);

    protected void HandleWheel(WheelEventArgs e) => Wheel?.Invoke(e);
 
    internal readonly record struct CanvasOffset(float Left, float Top);
    internal virtual ValueTask<CanvasOffset> GetCanvasOffsetAsync() => ValueTask.FromResult(default(CanvasOffset));
 
    private async Task ForwardTouch(TouchEventArgs args, Action<TouchEventArgs>? handler)
    {
        if (handler is null) return;
        var offset = await GetCanvasOffsetAsync();
        foreach (var point in args.ChangedTouches)
        {
            point.ClientX -= offset.Left;
            point.ClientY -= offset.Top;
        }
        handler(args);
    }

    protected Task HandleTouchStart(TouchEventArgs e) => ForwardTouch(e, TouchStart);

    protected Task HandleTouchMove(TouchEventArgs e) => ForwardTouch(e, TouchMove);

    protected Task HandleTouchEnd(TouchEventArgs e) => ForwardTouch(e, TouchEnd);

    protected void HandleTouchCancel(TouchEventArgs e) => TouchCancel?.Invoke(e);

    public abstract void Dispose();
}