BeginBufferedAnimation function

"BeginBufferedAnimation" returns NULL if "BufferedPaintInit" is not called for the thread.

BufferedPaintStopAllAnimations must be called when a BeginBufferedAnimation hwnd is being destroyed (even if EndBufferedAnimation has been called).  The BufferedPaint code depends on window timers set on the BeginBufferedAnimation hwnd - if that window is being destroyed, the corresponding timers will be destroyed as well.  If one neglects to call BufferedPaintStopAllAnimations when a BeginBufferedAnimation window is destroyed, memory and GDI resource may be leaked.

using System;
using System.Drawing;
using System.Runtime.InteropServices;
using System.Windows.Forms;

namespace BufferedAnimation
{
    public class BufferedAnimationControl : Control
    {
        public BufferedAnimationControl()
            : base()
        {
            this.SetStyle(ControlStyles.AllPaintingInWmPaint | ControlStyles.UserPaint, true);
            BufferedPaintInit();
        }

        ~BufferedAnimationControl()
        {
            BufferedPaintStopAllAnimations(this.Handle);
            BufferedPaintUnInit();
        }

        protected override Size DefaultSize
        {
            get
            {
                return  Size.Add(SystemInformation.IconSize, new Size(20,20));
            }
        }

        bool g_fCurrentState = true;
        bool g_fNewState = true;

        void StartAnimation(IntPtr hWnd)
        {
            g_fNewState = !g_fCurrentState;
            this.Invalidate(true);
        }

        private void PaintAnimationState(IntPtr hdc, bool state)
        {
            Graphics g = Graphics.FromHdc(hdc);
            using (Brush brush = new SolidBrush(this.BackColor))
                g.FillRectangle(brush, this.ClientRectangle);
            Icon stateIcon = state ? SystemIcons.Application : SystemIcons.Error;
            g.DrawIcon(stateIcon, 10, 10);
        }

        protected override void OnPaint(PaintEventArgs e)
        {
            base.OnPaint(e);
            IntPtr hdc = e.Graphics.GetHdc();
            if (hdc != IntPtr.Zero)
            {
                // See if this paint was generated by a soft-fade animation
                if (!BufferedPaintRenderAnimation(this.Handle, hdc))
                {
                    BP_ANIMATIONPARAMS animParams = new BP_ANIMATIONPARAMS();
                    animParams.cbSize = Marshal.SizeOf(animParams);
                    animParams.style = BP_ANIMATIONSTYLE.BPAS_LINEAR;

                    // Check if animation is needed. If not set dwDuration to 0
                    animParams.dwDuration = (g_fCurrentState != g_fNewState ? ANIMATION_DURATION : 0);

                    RECT rc = new RECT(this.ClientRectangle);
                    IntPtr hdcFrom, hdcTo;
                    IntPtr hbpAnimation = BeginBufferedAnimation(this.Handle, hdc, ref rc, BP_BUFFERFORMAT.BPBF_COMPATIBLEBITMAP, IntPtr.Zero, ref animParams, out hdcFrom, out hdcTo);
                    if (hbpAnimation != IntPtr.Zero)
                    {
                        if (hdcFrom != IntPtr.Zero)
                        {
                            PaintAnimationState(hdcFrom, g_fCurrentState);
                        }
                        if (hdcTo != IntPtr.Zero)
                        {
                            PaintAnimationState(hdcTo, g_fNewState);
                        }
                        g_fCurrentState = g_fNewState;
                        EndBufferedAnimation(hbpAnimation, true);
                    }
                    else
                    {
                        PaintAnimationState(hdc, g_fCurrentState);
                    }
                }
                e.Graphics.ReleaseHdc(hdc);
            }
        }

        protected override void OnPaintBackground(PaintEventArgs pevent)
        {
            //base.OnPaintBackground(pevent);
        }

        protected override void OnClick(EventArgs e)
        {
            base.OnClick(e);
            StartAnimation(this.Handle);
        }

        protected override void OnResize(EventArgs e)
        {
            base.OnResize(e);
            BufferedPaintStopAllAnimations(this.Handle);
        }

        #region Interop

        [DllImport("uxtheme")]
        private static extern IntPtr BufferedPaintInit();

        [DllImport("uxtheme")]
        private static extern IntPtr BufferedPaintUnInit();

        [DllImport("uxtheme")]
        private static extern IntPtr BeginBufferedAnimation(IntPtr hwnd, IntPtr hdcTarget, ref RECT rcTarget, BP_BUFFERFORMAT dwFormat, IntPtr pPaintParams, ref BP_ANIMATIONPARAMS pAnimationParams, out IntPtr phdcFrom, out  IntPtr phdcTo);

        [DllImport("uxtheme")]
        private static extern IntPtr EndBufferedAnimation(IntPtr hbpAnimation, bool fUpdateTarget);

        [DllImport("uxtheme")]
        [return: MarshalAs(UnmanagedType.Bool)]
        private static extern bool BufferedPaintRenderAnimation(IntPtr hwnd, IntPtr hdcTarget);

        [DllImport("uxtheme")]
        private static extern IntPtr BufferedPaintStopAllAnimations(IntPtr hwnd);

        [StructLayout(LayoutKind.Sequential)]
        private struct RECT
        {
            public int left;
            public int top;
            public int right;
            public int bottom;
            public RECT(Rectangle rc)
            {
                left = rc.Left;
                top = rc.Top;
                right = rc.Right;
                bottom = rc.Bottom;
            }
        }
       
        [StructLayout(LayoutKind.Sequential)]
        private struct BP_ANIMATIONPARAMS
        {
            public Int32 cbSize, dwFlags;
            public BP_ANIMATIONSTYLE style;
            public Int32 dwDuration;
        }

        private enum BP_BUFFERFORMAT
        {
            BPBF_COMPATIBLEBITMAP,
            BPBF_DIB,
            BPBF_TOPDOWNDIB,
            BPBF_TOPDOWNMONODIB
        }
       
        [Flags]
        private enum BP_ANIMATIONSTYLE
        {
            BPAS_NONE = 0,
            BPAS_LINEAR = 1,
            BPAS_CUBIC = 2,
            BPAS_SINE = 3
        }

        private const int ANIMATION_DURATION = 500;

        #endregion
    }

}