gdi+ Graphics::DrawImage really slow~~

Bitmap *bitmap = Bitmap::FromFile("XXXX",...);

int width = bitmap->GetWidth();
int height = bitmap->GetHeight();
DrawImage(bitmap,0,0,width,height);

SetStretchBltMode(hDC, COLORONCOLOR);
StretchDIBits(hDC, rcDest.left, rcDest.top,
    	rcDest.right-rcDest.left, rcDest.bottom-rcDest.top,
    	0, 0, width, height,
    	BYTE* dib, dibinfo, DIB_RGB_COLORS, SRCCOPY);

Bitmap bmp = new Bitmap(...)
TextureBrush myBrush = new TextureBrush(bmp)

private void Paint(object sender, PaintEventArgs e):
{
    //Don't draw the bitmap directly.
    //Only draw TextureBrush inside the Paint event.
    e.Graphics.FillRectangle(myBrush, ...)
}

DrawImage(bitmap,0,0);

DrawImage(bitmap, 0, 0, bitmap.GetWidth, bitmap.GetHeight);

class procedure TGDIPlusHelper.DrawCachedBitmap(image: TGPImage;
      var cachedBitmap: TGPCachedBitmap;
      Graphics: TGPGraphics; x, y: Integer; width, height: Integer);
var
   b: TGPBitmap;
begin
   if (image = nil) then
   begin
      //i've chosen to not throw exceptions during paint code - it gets very nasty
      Exit;
   end;

   if (graphics = nil) then
   begin
      //i've chosen to not throw exceptions during paint code - it gets very nasty
      Exit;
   end;

   //Check if we have to invalidate the cached image because of size mismatch
   //i.e. if the user has "zoomed" the UI
   if (CachedBitmap <> nil) then
   begin
      if (CachedBitmap.BitmapWidth <> width) or (CachedBitmap.BitmapHeight <> height) then
         FreeAndNil(CachedBitmap); //nil'ing it will force it to be re-created down below
   end;

   //Check if we need to create the "cached" version of the bitmap
   if CachedBitmap = nil then
   begin
      b := TGDIPlusHelper.ResizeImage(image, width, height);
      try
         CachedBitmap := TGPCachedBitmap.Create(b, graphics);
      finally
         b.Free;
      end;
end;

    if (graphics.DrawCachedBitmap(cachedBitmap, x, y) <> Ok) then
begin
       //The calls to DrawCachedBitmap failed
       //The API is telling us we have to recreate the cached bitmap
       FreeAndNil(cachedBitmap);
       b := TGDIPlusHelper.ResizeImage(image, width, height);
       try
          CachedBitmap := TGPCachedBitmap.Create(b, graphics);
       finally
          b.Free;
       end;

       graphics.DrawCachedBitmap(cachedBitmap, x, y);
    end;
 end;

Image imgPrintInvoice = new Image.FromFile("printer.png");
CachedBitmap imgPrintInvoiceCached = null;

...

int glyphSize = 16 * (GetCurrentDpi() / 96);

DrawCachedBitmap(imgPrintInvoice , ref imgPrintInvoiceCached , graphics,
      0, 0, glyphSize, glyphSize);