sbox-public/engine/Sandbox.Engine/Systems/UI/Panel/Panel.Razor.cs

using Microsoft.AspNetCore.Components;
using Microsoft.AspNetCore.Components.Rendering;

namespace Sandbox.UI;

public partial class Panel
{
	/// <summary>
	/// true when the tree should be re-rendered next frame.
	/// </summary>
	bool razorTreeDirty = true;
	string razorLastTreeChecksum = null;

	[Parameter] public RenderFragment ChildContent { get; set; }

	/// <summary>
	/// For razor panels, call when the state of the render tree has changed such that
	/// it would be a good idea to re-render the tree. You would usually not need to call
	/// this manually.
	/// </summary>
	public void StateHasChanged()
	{
		ThreadSafe.AssertIsMainThread();
		razorTreeDirty = true;
	}

	/// <summary>
	/// Overridden/implemented by Razor templating, contains render tree checksum to determine when the render tree content has changed.
	/// </summary>
	protected virtual string GetRenderTreeChecksum() => ChildContent == null ? null : "1";
	internal bool HasRenderTree => GetRenderTreeChecksum() is not null;

	PanelRenderTreeBuilder renderTree;

	/// <summary>
	/// Overridden/implemented by Razor templating to build a render tree.
	/// </summary>
	protected virtual void BuildRenderTree( RenderTreeBuilder tree )
	{
		ChildContent?.Invoke( tree );
	}

	int previousHash;

	/// <summary>
	/// By overriding this you can return a hash of variables used by the Razor layout, which
	/// will cause a rebuild when changed. This is useful when your layout uses a global variable
	/// because by adding it to a HashCode.Combine here you can easily trigger a build when it changes.
	/// </summary>
	protected virtual int BuildHash()
	{
		return 0;
	}

	/// <summary>
	/// A RenderFragment has been set on us, so our tree has potential changes now.
	/// Lets update and see.
	/// </summary>
	public void OnRenderFragmentChanged( Panel upTo )
	{
		if ( upTo == this )
			return;

		razorTreeDirty = true;
		Parent?.OnRenderFragmentChanged( upTo );
	}

	internal void InternalTreeBinds()
	{
		if ( renderTree == null )
			return;

		try
		{
			var hash = BuildHash();
			if ( previousHash != hash )
			{
				previousHash = hash;
				razorTreeDirty = true;
			}
		}
		catch ( System.Exception e )
		{
			Log.Warning( e, $"Error calculating hash on {GetType()} - {e.Message}" );
		}

		if ( renderTree.UpdateBinds() )
		{
			razorTreeDirty = true;
		}
	}

	/// <summary>
	/// Allows building render tree from outside of the class.
	/// </summary>
	internal RenderTreeBuilder InternalRenderTree()
	{
		if ( !HasRenderTree )
			return null;

		razorTreeDirty = false;

		renderTree ??= new PanelRenderTreeBuilder( this );
		razorLastTreeChecksum = GetRenderTreeChecksum();

		renderTree.Start();
		try
		{
			BuildRenderTree( renderTree );
		}
		catch ( System.Exception e )
		{
			Log.Warning( e, $"Error when building render tree on {GetType()} - {e.Message}" );
		}
		renderTree.Finish();

		return renderTree;
	}

	/// <summary>
	/// Called after the razor tree has been created/rendered.
	/// </summary>
	protected virtual void OnAfterTreeRender( bool firstTime )
	{

	}

	/// <summary>
	/// Delete all children generated by the Razor render tree.
	/// </summary>
	internal void ClearRenderTree()
	{
		renderTree?.Clear();
		renderTree = null;
	}
}