BitBlt is faster

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From: Calciu on 26 Jun 2008 10:53

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Even with BufferedGraphics, BitBlt is faster. I am saying this because with BufferedGraphics you still use g.DrawImage(myBitmap,x,y); wich is slower than BitBlt. I have done tests!

If you want to use BitBlt then you must use this approach:

[DllImport("gdi32.dll", ExactSpelling = true, SetLastError = true)]
public static extern IntPtr CreateCompatibleDC(IntPtr hDC);
[DllImport("gdi32.dll", ExactSpelling = true)]
public static extern IntPtr SelectObject(IntPtr hDC, IntPtr hObject);
[DllImport("gdi32.dll", ExactSpelling = true)]
public static extern IntPtr DeleteObject(IntPtr hObject);
[DllImport("gdi32.dll")]
private static extern bool BitBlt(IntPtr hdcDest,Int32 nXDest,Int32 nYDest,Int32 nWidth,Int32 nHeight,IntPtr hdcSrc,Int32 nXSrc,Int32 nYSrc,UInt32 dwRop);
private const uint SRCCOPY = 0x00CC0020;

IntPtr dcSrc = IntPtr.Zero;
Graphics gSrc = null;
IntPtr hBitmap = IntPtr.Zero;
private Bitmap backImage = null;

public Bitmap BackImage
{
get { return backImage; }
set
{
backImage = value;

if (dcSrc != IntPtr.Zero)
{
gSrc.ReleaseHdc(dcSrc);
gSrc.Dispose();
DeleteObject(hBitmap);
dcSrc = IntPtr.Zero;
}

if (backImage != null)
{
hBitmap = backImage.GetHbitmap();

Graphics clientDC = this.CreateGraphics();
IntPtr hdc = clientDC.GetHdc();
IntPtr memdc = CreateCompatibleDC(hdc);

SelectObject(memdc, hBitmap);
gSrc = Graphics.FromHdc(memdc);
dcSrc = gSrc.GetHdc();

clientDC.ReleaseHdc(hdc);
clientDC.Dispose();
}

this.Invalidate();
}
}

protected override void OnPaint(PaintEventArgs e)
{
Rectangle r = e.ClipRectangle;
if (backImage != null && showBackground)
{
if (r.X > backImage.Width || r.Y > backImage.Height)
return;
if (r.X + r.Width > backImage.Width)
r.Width = backImage.Width - r.X;
if (r.Y + r.Height > backImage.Height)
r.Height = backImage.Height - r.Y;

//e.Graphics.DrawImage(backImage, r, r, GraphicsUnit.Pixel); // the slower GDI+ way

IntPtr dcDst = e.Graphics.GetHdc();
BitBlt(dcDst, r.X, r.Y, r.Width, r.Height, dcSrc, r.X, r.Y, SRCCOPY);// the faster GDI BitBlt way
e.Graphics.ReleaseHdc(dcDst);
}
}

My problem is how to i release the hBitmap wich is as big as backImage but i'm sure i will find soon.

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