Catel - Part 4 of n: Unit testing with Catel

// --------------------------------------------------------------------------------------------------------------------
// <copyright file="VisualExtensions.cs" company="Catel development team">
//   Copyright (c) 2008 - 2011 Catel development team. All rights reserved.
// </copyright>
// <summary>
//   Extensions for the <see cref="Visual" />
// </summary>
// --------------------------------------------------------------------------------------------------------------------

using System;
using System.Reflection;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Interop;
using System.Windows.Media;
using Catel.Windows.Properties;
using log4net;

namespace Catel.Windows
{
    /// <summary>
    /// Extensions for the <see cref="Visual"/>
    /// </summary>
    public static class VisualExtensions
    {
        #region Variables
        /// <summary>
        /// The <see cref="ILog">log</see> object.
        /// </summary>
        private static readonly ILog Log = LogManager.GetLogger(MethodBase.GetCurrentMethod().DeclaringType);

        private static readonly Delegate _onVisualLoadedDelegate = Delegate.CreateDelegate(typeof(RoutedEventHandler), typeof(VisualExtensions), "OnVisualLoaded");
        #endregion

        /// <summary>
        /// Disables the hardware acceleration for the specified visual.
        /// </summary>
        /// <param name="visual">The visual.</param>
        /// <remarks>
        /// When the visual is not yet loaded, this method tries to subscribe to the <see cref="Control.Loaded"/> event so disabled the 
        /// hardware acceleration as soon as the control is loaded.
        /// </remarks>
        /// <exception cref="ArgumentNullException">when <paramref name="visual"/> is <c>null</c>.</exception>
        public static void DisableHardwareAcceleration(this Visual visual)
        {
            if (visual == null)
            {
                throw new ArgumentNullException("visual");
            }

            Type visualType = visual.GetType();
            var hwndSource = PresentationSource.FromVisual(visual) as HwndSource;
            if (hwndSource == null)
            {
                // Visual is now null, try to subscribe to the loaded event
                EventInfo loadedEvent = visualType.GetEvent("Loaded");
                if (loadedEvent != null)
                {
                    Log.Debug(TraceMessages.HardwareAccelerationCannotBeDisabledYet, visualType);
                    
                    loadedEvent.AddEventHandler(visual, _onVisualLoadedDelegate);
                }
                else
                {
                    Log.Warn(TraceMessages.FailedToDisableHardwareAcceleration, visualType);
                }
            }
            else
            {
                // Set to software only
                hwndSource.CompositionTarget.RenderMode = RenderMode.SoftwareOnly;

                Log.Debug(TraceMessages.DisabledHardwareAcceleration, visualType);
            }
        }

        /// <summary>
        /// Called when [visual loaded].
        /// </summary>
        /// <param name="sender">The sender.</param>
        /// <param name="e">The <see cref="System.EventArgs"/> instance containing the event data.</param>
        private static void OnVisualLoaded(object sender, RoutedEventArgs e)
        {
            Visual visual = (Visual)sender;

            EventInfo loadedEvent = visual.GetType().GetEvent("Loaded");
            loadedEvent.RemoveEventHandler(visual, _onVisualLoadedDelegate);

            DisableHardwareAcceleration((Visual) sender);
        }
    }
}