chinese_chess/Scripts/Entities/ChessBoard.cs

// Chessboard.cs
using System;
using Godot;
using ChineseChess;
using Godot.Collections;

public partial class ChessBoard : Node2D {
    public event EventHandler<Vector2> OnMouseClicked;
	public event EventHandler<Vector2> OnPosClicked;

	public Vector2 from = Vector2.Inf, to = Vector2.Inf;
	public Array<Vector2> canMovePos = new();

	public override void _Ready() {
	}

	public void Clear() {
		from = to = Vector2.Inf;
		QueueRedraw();
	}

	public void LoadBoard(CCBoard board) {
		board.OnRemove += (sender, piece) => {
			if (piece?.Data.TryGetValue("Godot", out object node) ?? false) {
				RemoveChild(node as Node);
			}
		};

		board.OnInsert += (sender, piece) => {
			ChessPiece chessPiece = null;
			if (piece.Data.TryGetValue("Godot", out object node)) {
				chessPiece = node as ChessPiece;
			} else {
				chessPiece = new((CCPiece)piece);
			}
			chessPiece.ShowBehindParent = true;
			AddChild(chessPiece);
		};

		board.OnMove += (sender, vals) => {
			from = PosTrans.transArrToPix * new Vector2(vals.From.X, vals.From.Y);
			to = PosTrans.transArrToPix * new Vector2(vals.To.X, vals.To.Y);
			QueueRedraw();
		};
	}

	public override void _Draw() {
		Color color = new(0.7f, 0.7f, 0.7f, 0.5f);
		DrawLine(from, to, color, PosTrans.pixGripSize / 5);
		DrawCircle(from, PosTrans.pixGripSize / 2.2f, color);
		foreach (Vector2 pos in canMovePos) {
			DrawCircle(pos, PosTrans.pixGripSize / 2.2f,
				 color.Inverted());
		}
    }

    public override void _Input(InputEvent @event) {
		if (@event is InputEventMouseButton mouseEvent &&
				mouseEvent.Pressed &&
				mouseEvent.ButtonIndex == MouseButton.Left) {
            OnMouseClicked?.Invoke(this, GetLocalMousePosition());
			OnPosClicked?.Invoke(this, (PosTrans.transArrToPix.AffineInverse() *
				GetLocalMousePosition()).Round());
		}
	}

	public static class PosTrans {
		public static readonly int pixGripSize = 32;
		public static readonly Transform2D transArrToPix = new(
			new Vector2(pixGripSize, 0),
			new Vector2(0, pixGripSize),
			new Vector2(-4, -4.5f) * pixGripSize
		);
	}
}