Why the use of 'RenderTargetBitmap' class makes GDI handle count increase?

Question

My understandings

1) The classes inside 'System.Windows.Media' uses directx for rendering. It will not use GDI+. 2) Only classes in 'System.Drawing' uses GDI+ for drawing.( This can cause GDI handle count increase.)

Issue

But when I use 'System.Windows.Media.Imaging.RenderTargetBitmap' for rendering a bitmap, the GDI count seems to be increased.

Why it happens so?

( Since I need to place these images on a button, and this button is part of the celltemplate of a Grid control, I want to reduce the GDI usage.)

DrawingVisual drawingVisual = new DrawingVisual();
DrawingContext drawingContext = drawingVisual.RenderOpen();
// Create Rectangle
Rect rect = new Rect(new System.Windows.Point(0, 0), new System.Windows.Point(100, 100));
// Draw Rectangle
System.Windows.Media.Pen pen = new System.Windows.Media.Pen();
pen.Brush = Brushes.Black;
pen.Thickness = 5;
drawingContext.DrawRectangle(Brushes.Black, pen, rect);             
drawingContext.Close();
RenderTargetBitmap bmp = new RenderTargetBitmap(100, 100, 96.0, 96.0, PixelFormats.Pbgra32);
//Render DrawingVisual 
bmp.Render(drawingVisual);

Answer 1

Looking around the net and some analysis, it seems that RenderTargetBitmap doesn't take advantage of hardware rendering(Direct X). It still uses GDI+ for rendering the bitmap offline.

It may be an exception to the common understanding about WPF rendering. But its surprise me that MSDN doesn't provide a clue anywhere regarding this.