ColorLegendWidget.cs

using UnityEngine;
using UnityEditor;
using System.Linq;

namespace RelationsInspector.Backend
{
	public struct ColorLegendEntry
	{
		public string text;
		public Color color;
	}

	public static class ColorLegendBox
	{
		static Vector2 padding = new Vector2( 4, 4 );

		public static Vector2 GetSize( string title, ColorLegendEntry[] entries )
		{
			return ColorLegend.GetSize( title, entries ) + 2*padding;	// padding is applied on both sides of the content
		}

		public static void Draw( Rect rect, string title, ColorLegendEntry[] entries )
		{
			GUI.Box( rect, GUIContent.none );
			var contentRect = new Rect( rect.x + padding.x, rect.y + padding.y, rect.width - 2 * padding.x, rect.height - 2 * padding.y );
			ColorLegend.Draw( contentRect, title, entries );
		}
	}

	static class ColorLegend
	{
		static GUIStyle titleStyle = EditorStyles.boldLabel;
		static GUIStyle entryLabelStyle = GUI.skin.label;

		public static Vector2 GetSize( string title, ColorLegendEntry[] entries )
		{
			Vector2 titleSize = titleStyle.CalcSize( new GUIContent( title ) );
			var entrySizes = entries.Select( x => entryLabelStyle.CalcSize( new GUIContent( x.text ) ) );
			float maxWidth = Mathf.Max( titleSize.x, entrySizes.Max( s => s.x ) + ColorRectWidget.GetSize().x );
			float height = titleSize.y + entrySizes.Sum( s => s.y );
			return new Vector2( maxWidth, height );
		}

		public static void Draw( Rect rect, string title, ColorLegendEntry[] entries )
		{
			var titleContent = new GUIContent( title );
			Vector2 titleSize = titleStyle.CalcSize( titleContent );
			var titleRect = new Rect( rect.x, rect.y, titleSize.x, titleSize.y );
			GUI.Label( titleRect, titleContent, titleStyle );

			var colorRectSize = ColorRectWidget.GetSize();

			for (int i=0; i<entries.Length; i++)
			{
				var colorRectOrigin = new Vector2( rect.x, rect.y + titleSize.y + colorRectSize.y * i );
				var colorRect = new Rect( colorRectOrigin.x, colorRectOrigin.y, colorRectSize.x, colorRectSize.y );
				ColorRectWidget.Draw( colorRect, entries[i].color );

				var labelOrigin = new Vector2( rect.x + colorRectSize.x, rect.y + titleSize.y + colorRectSize.y * i );
				var labelContent = new GUIContent( entries[ i ].text );
				var labelSize = entryLabelStyle.CalcSize( labelContent );
				var labelRect = new Rect( labelOrigin.x, labelOrigin.y, labelSize.x, labelSize.y );
				GUI.Label( labelRect, labelContent, entryLabelStyle );
			}
		}
	}

	static class ColorRectWidget
	{
		static Vector2 LayoutSize = new Vector2( 16, 16 );
		static Vector2 InnerOffset = new Vector2( 4, 4 );
		static Vector2 innerSize = new Vector2( 8, 8 );

		public static Vector2 GetSize()
		{
			return LayoutSize;
		}

		public static void Draw( Rect layoutSpace, Color color )
		{
			var colorRectOrigin = new Vector2( layoutSpace.x + InnerOffset.x, layoutSpace.y + InnerOffset.y );
			var outlineRectOrigin = new Vector2( colorRectOrigin.x - 1, colorRectOrigin.y - 1 );
			EditorGUI.DrawRect( new Rect( outlineRectOrigin.x, outlineRectOrigin.y, innerSize.x + 2, innerSize.y + 2 ), Color.black );
			EditorGUI.DrawRect( new Rect( colorRectOrigin.x, colorRectOrigin.y, innerSize.x, innerSize.y ), color );
		}
	}
}