Memory leak in WPF GDI Control

[andulv]

While using the control in a WPF project I ran into various out-of-memory exceptions after rendering several Scores.

It seems like memory for the previous generated bitmap is not released when a new bitmap is generated.

The code below is taken from OnRenderFinished in AlphaTabGdi.cs:

        using (Bitmap bitmap = ((GdiCanvas)_renderer.canvas).getImage())
        {
            Source = System.Windows.Interop.Imaging.CreateBitmapSourceFromHBitmap(
                bitmap.GetHbitmap(),
                IntPtr.Zero, Int32Rect.Empty,
                BitmapSizeOptions.FromWidthAndHeight(bitmap.Width, bitmap.Height));
            Width = bitmap.Width;
            Height = bitmap.Height;
        }

As far as I have understood, the call to bitmap.GetHbitmap() gives a pointer to unmanaged memory that must be freed after use.

I applied the following quick-fix / workaround.

    [System.Runtime.InteropServices.DllImport("gdi32.dll")]
    public static extern int DeleteObject(IntPtr hObject);

    IntPtr _currentlyAllocatedBitmap = IntPtr.Zero;

    // This method raises the Tap event 
    protected virtual void OnRenderFinished()
    {
        using (Bitmap bitmap = ((GdiCanvas)_renderer.canvas).getImage())
        {
            if (_currentlyAllocatedBitmap != IntPtr.Zero) 
             {
                DeleteObject(_currentlyAllocatedBitmap);
                _currentlyAllocatedBitmap=  IntPtr.Zero;
             }

            _currentlyAllocatedBitmap=bitmap.GetHbitmap();
            Source = System.Windows.Interop.Imaging.CreateBitmapSourceFromHBitmap(
                _currentlyAllocatedBitmap,
                IntPtr.Zero, Int32Rect.Empty,
                BitmapSizeOptions.FromWidthAndHeight(bitmap.Width, bitmap.Height));

            Width = bitmap.Width;
            Height = bitmap.Height;
        }

        RoutedEventArgs newEventArgs = new RoutedEventArgs(RenderFinishedEvent);
        RaiseEvent(newEventArgs);
    }

This quick-fix is far from perfect, and memory may probably still leak in some cases, but it solved the problems I were experiencing.

[Danielku15]

Thanks for the fix. I will take a look if there's a better solution to convert a GDI Bitmap into a WPF Image which allows immediate cleanup of the GDI stuff. I probably could copy the raw Bitmap Data into a WritableBitmap to resolve this problem but we'll see.